BASIC HYDRAULICS LEARNING ACTIVITY PACKET - Edl · PDF fileLEARNING ACTIVITY PACKET 4 ......

BASICHYDRAULICS

HYDRAULIC SPEED CONTROLHYDRAULIC SPEED CONTROL

LEARNINGACTIVITYPACKET

TM

BB831-XA04XEN

LEARNING ACTIVITY PACKET 4

HYDRAULIC SPEED CONTROL

INTRODUCTIONLAP 2 covered the speed control of actuators using a needle valve or by feathering

the DCV. This LAP will explain the details of why a needle valve or feathering a DCVcauses the flow rate to be reduced.

Also, this LAP will discuss two new valves: the flow control valve and the checkvalve. These valves will then be used to design a number of circuits that control actuatorspeed.

ITEMS NEEDEDAmatrol Supplied 1 85-BH Basic Hydraulic Training System 1 85-HPS Hydraulic Power Unit

School Supplied 1 Stopwatch 1 Allen Wrench Set

BB831-XA04XEN HYDRAULIC SPEED CONTROLCopyright © 2014 Amatrol, Inc. 2

FIRST EDITION, LAP 4, REV. BAmatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registeredtrademarks of Amatrol, Inc. All other brand and product names are trademarks or registered trademarks of theirrespective companies.Copyright © 2014, 2009 by AMATROL, INC.All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by anymeans, electronic, optical, mechanical, or magnetic, including but not limited to photographing, photocopying,recording or any information storage and retrieval system, without written permission of the copyright owner.Amatrol,Inc., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584www.amatrol.com

TABLE OF CONTENTS

SEGMENT 1 RELIEF VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4OBJECTIVE 1 Describe the function of a relief valve and give an applicationOBJECTIVE 2 Describe the operation of a direct-acting relief valve and give its schematic symbolOBJECTIVE 3 Describe how a relief valve is used for system protection

SKILL 1 Connect a relief valve in a circuit to limit pressure in the systemOBJECTIVE 4 Describe how a relief valve is used for speed control assistance

Activity 1 Relief valve operation with speed control

SEGMENT 2 CHECK VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18OBJECTIVE 5 Describe the function of a check valve and give an applicationOBJECTIVE 6 Describe the operation of three types of check valves and give their schematic symbol

Activity 2 Check valve operationSKILL 2 Design a circuit to provide bypass flow

SEGMENT 3 FLOW CONTROL VALVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28OBJECTIVE 7 Describe the function of the flow control valve and give an applicationOBJECTIVE 8 Describe the operation of a flow control valve and give its schematic symbol

SKILL 3 Connect and adjust a flow control valve to control speed of an actuatorOBJECTIVE 9 Describe the effect of actuator load changes on flow control valve operation

Activity 3 Effect of actuator load changes on flow control valve operation

SEGMENT 4 METER-IN AND METER-OUT CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39OBJECTIVE 10 Describe the operation of a meter-in flow control circuit and give an application

SKILL 4 Connect and operate a meter-in flow control circuitOBJECTIVE 11 Describe the operation of a meter-out flow control circuit and give an application

SKILL 5 Connect and operate a meter-out flow control circuit

SEGMENT 5 FLOW CONTROL CIRCUIT DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51OBJECTIVE 12 Define independent speed control and give an application

SKILL 6 Design an independent speed control circuitOBJECTIVE 13 Explain how speed control valves can be used to provide multiple speeds

SKILL 7 Design a two-speed actuator circuit

SEGMENT 6 FLOW RATE VS. CYLINDER SPEED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59OBJECTIVE 14 Describe how to calculate the extend speed of a hydraulic cylinder

SKILL 8 Calculate the extend speed of a hydraulic cylinder given its size and a flow rateOBJECTIVE 15 Describe how to calculate the retract speed of a cylinder

SKILL 9 Calculate the retract speed of a cylinder given its size and a flow rateOBJECTIVE 16 Describe how to calculate the stroke time of a cylinder

SKILL 10 Calculate the cylinder stroke time given its size and a flow rate


SEGMENT 1

RELIEF VALVES

OBJECTIVE 1 DESCRIBE THE FUNCTION OF A RELIEF VALVEAND GIVE AN APPLICATION

Relief valves are used in hydraulic systems to allow pump flow tobypass the system and flow directly to the reservoir. Two applicationsare:

• Protecting system components from high pressure.

• Assisting flow control valves in controlling actuator speed.

A typical relief valve is shown in figure 1.


Figure 1. Typical Relief Valve Used in Industrial Hydraulics

OBJECTIVE 2 DESCRIBE THE OPERATION OF A DIRECT-ACTINGRELIEF VALVE AND GIVE ITS SCHEMATIC SYMBOL

There are two relief valve designs commonly used in hydraulicapplications. One type is the direct-acting design. The other type is apilot-operated or two-stage relief valve to be described in a later LAP.The basic function of each valve type is the same: each opens at a presetpressure to allow flow to return to the reservoir. However, theconstruction of each is different.

Three types of direct-acting relief valves are shown in figure 2. Eachconsists of a body with two ports: an inlet and an outlet. Inside the bodyis a movable member that is held in the closed position by a spring.


SPOOL TYPE BALL TYPE

TT

P

P

POPPET TYPE

T

P

Figure 2. Direct-Acting Relief Valve Types

Using the poppet type, also called the dart type, figure 3 shows theoperation of the direct-acting relief valve when the pressure at the inletport reaches a certain level. The pressure creates enough force to pushthe poppet off the seat and allow oil to flow through to the outlet. Byadjusting the compression on the spring with an adjuster, the pressurelevel where the valve opens can be changed.

The schematic symbol is the same for the direct-acting andpilot-operated relief valves and is shown in figure 4. Notice that theexplanation of the symbol in figure 4 shows what each part of thesymbol means. This valve is a normally closed valve. You can tell thisfrom the symbol because the arrow in the block is shown not connectingthe inlet and outlet.

The dashed line is an internal line called a pilot line which causes the valve to open (raises the arrow). The spring indicates that the valveopens at a certain pressure. The angled arrow through the spring tells you that the pressure is adjustable.

Finally, notice that the pilot line connects to the valve’s inlet. Thistells you that the valve senses inlet or upstream pressure only.


TO RESERVOIR

VALVE OPENVALVE CLOSED

PRESSUREINLET POPPET SPRING

BODYOUTLET ADJUSTER

Figure 3. Basic Operation of a Direct-Acting Relief Valve

SYMBOL EXPLANATION

INLET

ADJUSTABLE

OUTLET

NORMALLYCLOSED

PILOTTO OPEN

Figure 4. Relief Valve Schematic Symbol

OBJECTIVE 3 DESCRIBE HOW A RELIEF VALVE IS USEDFOR SYSTEM PROTECTION

Almost all hydraulic systems have a relief valve in the circuit to actas a safety device in case the pressure becomes too high. High pressurecan occur in a hydraulic system if the pump’s flow is blocked for somereason.

The relief valve’s primary purpose is to limit system pressure duringnormal operation as well as when a component malfunctions. During thenormal operation of a hydraulic system, the flow to the circuit will beblocked for periods of time. This includes when the directional controlvalve is in a blocked center condition, when a cylinder becomesextended or retracted, or when an actuator is stalled by an excessive load.

SKILL 1 CONNECT A RELIEF VALVE IN A CIRCUIT TO LIMITPRESSURE IN THE SYSTEM

q 1. Set up the cylinder reciprocation circuit shown in figures 5 and 6.

In this circuit, you will cycle the cylinder using a directionalcontrol valve. During each part of the cycle, you will observe theflow from the relief valve’s outlet to determine whether it is openor closed.

Although all relief valves must be drained, most are internallydrained. The relief valve is understood to be internally drainedwhen no external drain line is drawn. Notice that this relief isexternally drained and must have the drain connected to the returnmanifold. This is because this valve is also used in the Amatroltrainer to perform the function of a sequence valve in a later LAP.


Procedure OverviewIn this procedure, you will connect a pilot-operated

relief valve to act as a safety device to limit the pressure in the system whenever the pump’s flow is blocked by thecircuit. This skill will also show that the relief valveperforms this function several times during a normal cycle.

Notice that this relief valve has its ports numbered. Port 1 is theinlet, port 2 is the outlet and port 3 is the drain.


HYDRAULIC INSTRUMENTATION PANEL

GAUGE A GAUGE B GAUGE CFLOWMETER

SUPPLYMANIFOLD

RETURNMANIFOLD

HYDRAULIC ACTUATOR MODULE

CYLINDER

A

B

A

B

CYLINDER

FLOWCONTROL

#1

FLOWCONTROL

#2

MOTOR

BASIC HYDRAULIC VALVE MODULE

1

2

3

1

2

3

A B

B A

B A

AA B

IN

OUT

RELIEF \ SEQUENCEVALVE

PRESSURE REDUCINGVALVE

VALVE

CHECK VALVE #1

CHECK VALVE #2

D.C.V.#1

NEEDLE

DRAINLINE

Figure 5. Pictorial of the Circuit for Observing Relief Valve Flow

q 2. Perform the power unit checkout procedures.

q 3. Close the shutoff valve.

q 4. Turn on the power unit and set the power unit’s relief valve to 500psi/3450 kPa.

A fixed displacement pump will continue to push oil into the linescausing the pressure to rise until a line bursts or the electric motorstalls. The relief valve avoids this problem by opening at some safe pressure level and allowing the flow of oil to dump back to thereservoir.

q 5. Open the shutoff valve and set the pressure of relief valve A (theone shown in figures 5 and 6) at 400 psi/2760 kPa.

This is done by turning the adjustment knob of relief valve A untilthe pressure at Gauge A shows 400 psi/2760 kPa.


SUPPLYMANIFOLD

RETURNMANIFOLD

12

3

RELIEFVALVE A

GAUGEA

DRAIN SMALLBORE

CYLINDEROUTIN

IN

OUT

A

B

Figure 6. Schematic of Circuit for Observing Relief Valve Flow

NOTEA drain line is shown in a schematic diagram as a dotted line,

as shown in figure 6.

q 6. Test the operation of the relief valve by extending and retractingthe cylinder. As you do this, notice when relief valve A is closed,the flowmeter reads zero flow and when relief valve A is open, theflowmeter reads full pump flow. Observe the pressure and reliefvalve status (opened or closed) for each condition.

You should have observed that the relief valve opens when theflow to the system is deadheaded or blocked. This occurs when the cylinder is extended, retracted, or the DCV is centered.

Figure 7 shows what happens when the flow has been deadheadedor blocked. The oil from the pump continues to flow into thesupply line even though it is blocked. As the pump continues topush oil into the supply line, the oil pressure rises rapidly to 400psi / 2760 kPa. Because 400 psi / 2760 kPa is the pressure settingof relief valve A, it opens when the pressure at the inlet reaches apressure of 400 psi/2760 kPa and allows the flow to dump to thereservoir, stopping the rise in pressure.


NOTEWhen the cylinder is fully extended or retracted, hold the

DCV’s lever actuated while you make the flow and pressurereadings.

CIRCUITCONDITION

GAUGE A(psi/kPa)

RELIEF VALVE STATUS(open/closed)

Cylinder extending

Cylinder extended

Cylinder retracting

Cylinder retracted

DCV centered

q 7. Adjust relief valve A to another setting such as 300 psi/2070 kPa.

q 8. Then repeat step 6 to see if the relief valve’s pressure setting hasany effect on when the relief valve is open and closed.

You should observe no difference in the operation of the reliefvalve.

q 9. Reduce the power unit relief valve to the minimum setting, closethe shutoff valve and turn off the power unit.

q10. Move the handle of the DCV back and forth to remove anypressure in the circuit.


IN

OUT

A

BOIL FLOW IS

STOPPED

CYLINDERFULLY

RETRACTEDM

RELIEFVALVE A

GAUGE A400psi / 2070kPa

DCVSHIFTED

SYSTEM RELIEF VALVE SETAT 500psi / 3450kPa(DOES NOT OPEN)

Figure 7. Relief Valve A Operating as a Pressure Limiting Device

NOTEIt is important to understand that when the relief valve is said

to be open, this means that the relief valve has opened farenough to allow the full pump flow to go through it. This does not mean that the valve is opened as far as it can go.

Instead, the valve increases its opening until the full flow ofthe pump can go through it. The pressure at which this occurs iscontrolled by the relief valve’s spring.

OBJECTIVE 4 DESCRIBE HOW A RELIEF VALVE IS USEDFOR SPEED CONTROL ASSISTANCE

Another application for the relief valve is to work with the needlevalve in controlling the speed of an actuator. This is accomplished byrestricting pump flow with the needle valve, increasing pressure to alevel that causes the relief valve to partially open and dump a part of thepump’s flow. The remaining pump flow goes to the actuator. As a result,the actuator moves at a slower speed.

This range of pressure between fully closed and fully opened isusually very small (i.e. 50 psi). When you set the relief valve pressure,you are actually setting the full open pressure. This is when all flow isgoing through the valve. But, the relief valve actually starts to open at aslightly lower pressure. This is called the cracking pressure.

If the pressure downstream in the circuit increases to a point between the cracking pressure and downstream pressure, some part of the pumpflow will be directed over the relief valve. For example, in figure 8, thefull open pressure of the relief valve is 1000 psi. However, the crackingpressure is 980 psi.


P

R

A

B

SET FOR1000 PSI

3 GPM

DCVSHIFTED

990PSI

M

970PSI

560PSI

540PSI 40

PSI

2 GPM

5 GPM

NEEDLEVALVE

EXTENDING

LOAD

Figure 8. Relief Valve Operating with a Needle Valve for Speed Control

Without the needle valve, the pressure would be about 560 psi whilethe cylinder is extending due to the load and the DCV. This means thatfull pump flow would be going to the cylinder if the needle valve werenot in the circuit. By putting the needle valve in the circuit, we can create another pressure drop to make the system pressure rise to 990 psi whichis enough to cause the relief valve to partially open and divert some ofthe flow across the relief valve.

Activity 1. Relief Valve Operation With Speed Control

q 1. Connect the circuit shown in figure 9.

In this circuit, the needle valve will control the flow to the motor.The externally drained relief valve will be used to show that theexcess flow not used by the circuit is diverted over the relief valve.


Procedure OverviewIn this procedure, you will demonstrate how the needle

valve and relief valve combine to control the flow rate in acircuit. To do this, you will measure the pressure when therelief valve first starts to open and then observe the flow as pressure increases to the relief valve’s pressure setting.

NOTEThe hose with the open-end fitting is shown in figure 10. The

open-end fitting being held over the opened filler/breather isillustrated in figure 11.

NOTEVerify that the flywheel is removed from the motor shaft. If it is

not, use a 3/32-inch allen wrench to remove it as you did in LAP2 (Skill 4).


SUPPLYMANIFOLD

RETURNMANIFOLD

A BSHUTOFF

VALVE

12

3

RELIEFVALVE A

GAUGEA

FILLERBREATHER

PORT

OPEN ENDFITTING

NEEDLEVALVE

MOTOR

Figure 9. Schematic of Circuit for Demonstrating the Operation of theNeedle Valve/Relief Valve Combination

Figure 10. Hose End with Open-End Quick-Connect Fitting


q 3. Close the needle valve completely.

q 4. Turn on the power unit and adjust the power unit relief valve to500 psi/3447 kPa.

q 5. Open the shutoff valve.

q 6. Adjust the setting of relief valve A until Gauge A reads 350psi/2415 kPa. This is the full flow setting of the relief valve.

q 7. Open the needle valve completely by turning its adjustment knobfully CCW.

You should observe that the pressure at gauge A drops low enough to cause the relief valve to close and direct the pump’s full flow tothe motor.

The motor is now running at full speed.


Figure 11. Using the Open-End Fitting to View Flow Returning toReservoir Through the Filler/Breather Opening

CAUTIONBefore going to step 5, be sure the filler/breather cap has

been removed and the hose with the open-end fitting is directedinto the open reservoir.

q 8. As the motor is running, slowly turn the needle valve knob CW.

As you do this, observe the flow from the outlet of relief valve A.Record the pressure at Gauge A where the relief valve first starts to open. This is the cracking pressure.

Cracking Pressure _______________________________(psi/kPa)

The cracking pressure should be approximately 330 psi / 2277 kPa.

q 9. Continue to slowly turn the needle valve’s knob CW. Observe theflow through the relief valve and the speed of the motor.

You should observe that the motor slows down as the amount offlow through the relief valve increases.

When the pressure stops increasing at Gauge A, you have reachedthe relief valve’s pressure setting. This is where full flow is goingthrough the relief valve. The motor should then stop.

Relief Valve Pressure Setting_______________________(psi/kPa)

This should be the same pressure you set in step 6 (350 psi/2415kPa).

q10. Now change the pressure setting of relief valve A to 400 psi/2760kPa.

q11. Repeat steps 7-9 to see if the difference between system pressureand cracking pressure changes when the relief valve setting isdifferent.

Cracking Pressure _______________________________(psi/kPa)

The cracking pressure should be approximately 380 psi / 2622 kPa.

Relief Valve Pressure Setting_______________________(psi/kPa)

This should be the pressure you set in step 10 (400 psi / 2760 kPa).

You should find that the difference does not change.

q12. Reduce the power unit relief valve to minimum, turn off the power unit and close the shut-off valve.

q13. Remove the open-end quick-connect fitting and replace the cap onthe filler-breather.


SEGMENT 1 SELF REVIEW


1. The primary purpose of a relief valve is to _________system pressure.

2. When using a needle valve to control speed, excess pumpflow is directed over the _______ valve.

3. When operating in a flow control circuit, the speed of theactuator ___________ when the flow through the reliefvalve increases.

4. The two types of relief valves are ______________ andpilot-operated.

5. Turning the adjustment knob on a relief valve changes thecompression on the __________.

6. The __________ pressure is the point where the relief valvestarts to open.

SEGMENT 2

CHECK VALVES

OBJECTIVE 5 DESCRIBE THE FUNCTION OF A CHECK VALVEAND GIVE AN APPLICATION

The check valve is a valve that allows fluid to flow in one directionand completely blocks flow in the other direction. It is considered to be a one-way directional control valve. Figure 12 shows a check valve usedwith the Amatrol 850 Series trainer.

The check valve is one of the most commonly used hydraulic valves. The circuit shown in figure 13 shows four common applications:

• Holding Prime - It is common for the oil to drain out of the inlet lineof a hydraulic pump when it has not been run for a long period. Thisis called “losing the prime of the pump.”Most larger pumps have difficulty regaining prime because theatmospheric pressure is not enough to push the oil up the supply tube to the pump’s inlet. A check valve is often installed in the inlet lineto hold the oil in the line.

• Avoid Pump Reversal - There are some types of hydraulic circuitswhere the oil in the circuit will be forced through the pumpbackwards if the electric motor is turned off. Many pumps can bedamaged if they are driven backwards. To avoid this problem, acheck valve is often installed at the outlet of the pump to keep the oil pressure in the circuit from driving the pump in the reverse direction.


Figure 12. Check Valve Used in the 850 System

• Bypass - Check valves are often used in circuits to bypass the flowaround certain components in one direction. This allows thecomponent to control the circuit’s operation in one direction andhave no effect in the other direction.

• Back Pressure - Many larger directional control valve designs use oilpressure to shift the spool. With some designs there is a minimumsystem pressure that must exist in order to shift the spool. A checkvalve is often placed in the tank port to create a back pressuresufficient to shift the spool.

Check valves are also used in other applications for holdingactuators locked in position and providing a free flow of oil to ahydraulic motor as it decelerates to a stop. These applications will beexplored in later LAPs.


1. HOLDSPUMPPRIME

2. AVOIDSREVERSALOF PUMP

4. GENERATESBACK- PRESSURE

IN THE SYSTEM

3. BYPASSESNEEDLEVALVE IN

ONE FLOWDIRECTION

Figure 13. Four Common Check Valve Applications

OBJECTIVE 6 DESCRIBE THE OPERATION OF THREE TYPESOF CHECK VALVES AND GIVE THEIR SCHEMATIC SYMBOL

There are three common types of check valves used in hydraulics:

• Ball

• Poppet

• SwingCross-section sketches of each type are shown in figure 14. These

three valves all perform the same function: oil flows freely in onedirection and is blocked in the other direction.


BALL CHECK VALVE POPPET CHECK VALVE

SWING CHECK VALVE

BODY BALL SPRING POPPET

FLAPPER

FLOW BLOCKED FLOW BLOCKED

FLOW BLOCKED

Figure 14. Types of Check Valves

The check valve schematic symbol, shown in figure 15, is the samefor all three types.


CHECK VALVE

OR

INDICATESBLOCKED

FLOWRIGHT

TO LEFT

DENOTESFREE FLOW

LEFT TORIGHT

FREE FLOW

FREE FLOWDENOTESA SPRINGREQUIRED

SYMBOL EXPLANATION

Figure 15. Check Valve Symbol with Explanation

Activity 2. Check Valve Operation

q 1. Set up the circuit shown in figure 16.

In this circuit, the check valve will open in one direction to allowoil to flow through the DCV. In the other direction, it will stopflow.

To hook up the check valve correctly, connect it as shown in theschematic in figure 16.


q 3. Turn on the power unit and increase the relief valve’s pressuresetting to 300 psi/2070 kPa.



Procedure OverviewIn this procedure, you will demonstrate that a check

valve stops flow in one direction and allows it to flow freelyin the other direction.

IN

OUT

IN

OUT

A

B

B

A

Figure 16. Check Valve Test Circuit

q 5. Push in the lever of the DCV and observe the flow meter reading.

Flow Rate ___________________________________(gpm / lpm)

You should observe that the check valve is now full open, asshown in figure 17. You can tell this because the flow meter isreading the pump flow (approximately 2.6 gpm / 9.8 lpm).

This check valve uses a poppet and spring to control the flow offluid through the valve. The spring is only strong enough to allowthe poppet to block the passageway. A very low pressure can pushit open.


VALVEBODY

SPRING

FREEFLUIDFLOW

POPPET

FREE FLOW DIRECTION

Figure 17. Free Flow Operation of a Check Valve

q 6. Now pull out on the lever of the DCV and observe the flow meterreading.

Flow Rate ___________________________________(gpm / lpm)

You should observe that the check valve is blocked in thisdirection, as shown in figure 18. You can tell this because the flow meter reading is zero.

When the fluid tries to flow in the other direction, it pushes thepoppet harder against the seat (figure 18). This completely blocksoff the fluid flow through the check valve. This direction is calledthe “checked” or “blocked” direction. In the checked direction,these valves leak very little, or not at all.

q 7. Release the DCV lever.

q 8. Repeat steps 5-7 several times to further test the operation of thecheck valve.

q 9. Reduce the relief valve setting to a minimum, turn off the powerunit and close the shutoff valve.



VALVEBODY

SPRING

FLUIDFLOW

BLOCKED

POPPET

BLOCKED FLOW DIRECTION

Figure 18. Block Flow Operation of a Check Valve

SKILL 2 DESIGN A CIRCUIT TO PROVIDE BYPASS FLOW

q 1. Complete the design of the circuit shown in figure 19 so thecylinder can be reciprocated with a directional control valve. Thecylinder should extend at a slow speed (adjustable by the needlevalve) and retract at a high speed.

q 2. Connect your circuit design on the 850 Series trainer using thesmall bore cylinder.


q 4. Turn on the power unit and increase the relief valve’s pressuresetting to 300 psi/2070 kPa.


q 6. Close the needle valve completely. Then open it 1/2 turn.

This will set the needle valve for a slow cylinder speed.


Procedure OverviewIn this procedure, you will design a circuit that will use

a check valve in a basic application.

IN

OUT

A

B

Figure 19. Partial Schematic

q 7. Extend and retract the cylinder and observe its speed in bothextension and retraction. Record below whether the speed is fast or slow for each direction of motion.

Speed Extending _____________________________ (Fast/Slow)

Speed Retracting _____________________________ (Fast/Slow)

You should observe that the cylinder speed is faster duringretraction, because the check valve is bypassing the flow aroundthe needle valve.

The circuit you have designed duplicates the function of a flowcontrol valve.

q 8. Now try adjusting the needle valve to another flow setting byclosing it 1/4 turn. Then cycle the cylinder and observe the speedof the cylinder in retraction and extension.

The retract speed should stay the same but the extend speed should be slower than it was in step 7.

q 9. Reduce the relief valve’s pressure setting to minimum and turn offthe power unit.

q10. Reverse the position of the hose ends at the check valve to seewhat effect this has on the operation.

q11. Turn on the power unit and increase the relief valve’s pressuresetting to 300 psi / 2070 kPa.

q12. Now extend and retract the cylinder and observe its speed. Noticethe change in the cylinder speed in each direction caused by thereversed check valve. Observe whether the speed is fast or slow for each direction of motion.

Speed Extending _____________________________ (Fast/Slow)

Speed Retracting _____________________________ (Fast/Slow)

You should observe that the cylinder speed is faster duringextension because the hoses have been reversed causing the checkvalve to be reversed.

q13. Reduce the relief valve’s pressure setting to minimum. Turn offthe power unit and close the shutoff valve.





1. The check valve is a(n) ______ way directional controlvalve.

2. Check valves are used to hold prime, avoid pump reversal,________, and provide back pressure.

3. The direction through a check valve that allows flow iscalled ______________ direction.

4. The three types of check valves used in hydraulic systemsare the _________, ___________, and __________ types.

5. The poppet type check valve uses a(n) _________ to holdthe poppet on the seat.

6. A check valve is designed to provide __________ in onedirection only.

SEGMENT 3

FLOW CONTROL VALVES

OBJECTIVE 7 DESCRIBE THE FUNCTION OF THE FLOW CONTROL VALVEAND GIVE AN APPLICATION

The flow control valve used in the 850 Series trainer combines aneedle valve and check valve together in one valve body to restrictflow in one direction and allow free flow in the other direction. Atypical flow control valve is shown in figure 20.

The flow control valve is used with bi-directional actuators to makethe speed in one direction different from the other.


Figure 20. Flow Control Valve with Quick-Connect Fittings

OBJECTIVE 8 DESCRIBE THE OPERATION OF A FLOW CONTROL VALVEAND GIVE ITS SCHEMATIC SYMBOL

The flow control valve consists of a body with an inlet and outletport, an adjustment screw with a tapered end, an adjustment knob, acheck valve poppet, and a spring, as shown in figure 21.

The two symbol techniques used for the flow control valve areshown in figure 22.


SPRING POPPET

ADJUSTMENTKNOB

VALVEBODY

NEEDLEVALVE

DIRECTIONOF

CONTROLLEDFLOW

DIRECTIONOF

FREE FLOW

Figure 21. Construction of a Flow Control Valve

OR

CONTROLLEDFLOW

INDICATESORIFICE

INDICATESADJUSTABLE

FLOW

FREEFLOW

CHECKVALVE

INDICATESIN SAME

ENVELOPE(BODY)

SYMBOL EXPLANATION

Figure 22. Flow Control Valve Symbol with Explanation

SKILL 3 CONNECT AND ADJUST A FLOW CONTROL VALVETO CONTROL SPEED OF AN ACTUATOR

q 1. Set up the circuit shown in figure 23.

In this circuit, the flow control valve will control the flow to abi-directional motor. Motor speed will be controlled in onedirection and run at full speed in the other direction.

q 2. If not already done, remove the flywheel from the shaft of themotor.


q 4. Turn on the power unit and adjust the power unit relief valve to300 psi/2070 kPa.

q 5. Close the flow control valve completely by turning the adjustmentknob fully CW. Then open it 1/2 turn.



Procedure OverviewIn this procedure, you will connect a flow control valve

in a bi-directional actuator circuit to control the actuatorspeed in one direction only.

SUPPLYMANIFOLD

RETURNMANIFOLD

DIRECTIONALCONTROL

VALVE

MOTOR

FLOWMETER

IN

OUT

A

BA B

FLOWCONTROL

VALVE

HOSE AHOSE B

SHUTOFFVALVE

Figure 23. Schematic of a Flow Control Valve in a Motor Circuit

q 7. Push in on the lever of the DCV to run the motor and hold it. Themotor should run slowly.

As the motor is running, experiment with your ability to control thespeed of the motor by adjusting the flow control valve’s orificesetting.

As you do this, excess pump flow is being diverted through therelief valve on the power unit.

Fluid entering the flow control valve in the direction of controlledflow is forced to flow across the needle valve, as shown in figure24. It cannot flow across the check valve, because the poppetblocks flow in that direction. The amount of flow, and therefore,the speed of the actuator, can then be controlled by adjusting theopening of the adjustment screw.

q 8. As the motor is running, adjust the flow control valve setting sothe flowmeter reads 0.5 gpm / 1.9 lpm.

The motor should still be running slowly.


ADJUSTMENT KNOBCONTROLS FLUID FLOW

POPPET BLOCKSFLUID FLOW IN

THIS DIRECTION

FLUIDFLOW

MOTORTURNING

IN OUT

Figure 24. Flow Control Valve Controlling Flow to a Motor

q 9. Now reverse the direction of flow and motor rotation by pullingthe lever of the DCV out.

Observe the flow rate and the speed of the motor. Because the flow rate through the flow control valve is in the free-flow direction,full pump flow should be going through the motor causing it to run at high speed.

Fluid entering the flow control valve in the direction of free flowcan flow in two paths. It can flow across the opening of theadjustment screw and across the check valve poppet, as shown in figure 25. Because the poppet of the check valve opens fully tooffer very little resistance, most of the flow will take this path. The pump flow will then flow to the motor.

q10. Try to slow down the motor by turning the flow control valve’sadjustment CW.

You should observe that the flow control valve cannot control orstop flow in the reverse direction, because its check valve allowsflow to bypass the flow control valve’s variable orifice.

q11. Release the lever of the DCV.


POPPET LETS FLUIDFLOW FREE IN THIS

DIRECTION

MOTORTURNING

INOUTFLUIDFLOW

Figure 25. Free Flow Operation of a Flow Control Valve

q12. Perform the following substeps to change the flow control valve’sconnections.A. Reduce the power unit relief valve’s setting to minimum.B. Turn off the power unit.C. Open the flow control valve 1/2 turn.D. Reverse the position of the hose ends at the flow control valve

by connecting hose A end to flow control port B and hose Bend to flow control port A. This should allow control of motorspeed in the other direction.

E. Turn on the power unit and set the pressure to 300 psi/2070kPa.

q13. Push in on the lever of the DCV again and hold it. Observe theflow rate and speed of the motor.

Because the oil flows freely through the flow control valve, themotor speed should be fast and the flow meter should indicate fullpump flow.

q14. As the motor is running in this direction, experiment with yourability to adjust the speed of the motor by adjusting the flowcontrol valve setting CW.

You should observe that this has no effect.

q15. Open the flow control valve 1/2 turn.

q16. Now reverse the direction of flow and motor rotation by pullingthe lever of the DCV completely outward. Observe the flow rateand speed of the motor.

You should observe low flow and low speed because flow is being restricted to the motor.

q17. As the motor is running in this direction, experiment with yourability to control speed by adjusting the flow control valve’sorifice setting.

You should now observe that you can control the speed of themotor in this direction.

q18. Release the lever of the DCV, reduce the power unit relief valvesetting to minimum and turn off the power unit.



OBJECTIVE 9 DESCRIBE THE EFFECT OF ACTUATOR LOAD CHANGESON FLOW CONTROL VALVE OPERATION

Unfortunately, setting a flow control valve to a specific flow ratedoes not guarantee that the flow will stay constant. One of the factorsthat causes the flow through the flow control valve to change is a changein the actuator load. This happens because the pressure at the reliefvalve’s inlet is made up of the pressure drop caused by the flow controlvalve, fluid friction, and load. If the load increases, for example, thepressure at the relief valve’s inlet will increase and cause more flow togo through the relief valve. This causes the flow to the actuator todecrease and the actuator slows down. Similarly, if the load decreases,the speed of the actuator will increase.

In many circuits, the actuator load is fairly constant and some speedvariation is not harmful. For these situations, these valves work very well and are a very inexpensive solution. However, where loads will change,a special type of flow control valve called a pressure-compensated flowcontrol valve must be used. This valve is described in a later LAP.

Activity 3. Effect of Actuator Load Changes on Flow ControlValve Operation

q 1. Set up the circuit in figure 26.

This circuit uses a flow control valve to control the flow to extenda cylinder. Gauges B and C will be used to measure the loadpressure across the cylinder. Gauge A will be used to measure therelief valve pressure.

The load device, as shown in figure 27, should now be attached.This device will allow you to put a load on the actuator’s rod. Byturning the sockethead screws on the load device CW, you willincrease the load on the cylinder.


Procedure OverviewIn this procedure, you will demonstrate that the flow

rate through a standard (non-compensated) flow controlvalve will change while the valve is controlling flowwhenever the actuator load changes.

NOTEIf the load spring is attached to the cylinder load block, you

must remove it before continuing. See LAP 3 (Skill 2) if you donot remember how this is done.

q 2. Using a socket-head wrench (3/16-inch), turn both of the sockethead cap screws on the load device CCW, as shown in figure 27,until they are both loose. This will remove all load on the cylinderrod.


SUPPLYMANIFOLD

RETURNMANIFOLD

DIRECTIONALCONTROL

VALVE

GAUGE A

GAUGE B

GAUGE C

CYLINDER

LOADDEVICE

LOCATE TEE'S AT THECYLINDER PORTS

EXACTLY AS SHOWN

TEE

A

B

FLOWCONTROL

VALVESHUTOFF

VALVE

IN

OUT

A

B

Figure 26. Schematic of Circuit for Measuring the Effect of LoadChanges on Flow Control Valve Operation

Figure 27. Adjusting the Cylinder Load Device


q 4. Turn on the power unit and increase the relief valve setting to 500psi/3447 kPa.


q 6. Close the flow control valve completely and then open it 1/2 turn.

q 7. Extend and retract the cylinder using the DCV to test its operation.

q 8. Adjust the flow control valve’s setting so that the cylinder takesabout two seconds to extend. Cycle the cylinder to test the speedand use a stopwatch to measure the time. Then leave the cylinderin the retracted position.

q 9. Now extend the cylinder again and observe the readings of Gauges A, B, and C as the cylinder is extending. Record your readings inthe no load row.

q10. Use the following steps to increase the load to a light load of 150psi/1035 kPa.A. Turn the load device’s cap screws CW, as shown in figure 27,

about 1/4 turn each.B. Extend the cylinder again and observe the readings of gauges B

and C. The load across the cylinder is indicated by the pressuredifference between Gauges B and C.

C. Continue to adjust the friction load device by turning the capscrews until the pressure difference between Gauges B and C is approximately 150 psi/1035 kPa while the cylinder isextending. Cycle the cylinder several times, if needed, to makethis adjustment.

D. Leave the cylinder in the retracted position.You have now set the light load on the cylinder.


WARNINGKeep your hands and fingers away from the load device when

you are operating the cylinder. Do not attempt to makeadjustments while the cylinder is moving.

LOADEXTENDSTROKE

TIME(seconds)

GAUGE APRESSURE

(psi/kPa)

GAUGE BPRESSURE

(psi/kPa)

GAUGE CPRESSURE

(psi/kPa)

No Load

Light Load

Heavy Load

q11. Now extend the cylinder and measure, using a stopwatch, the timerequired to extend the cylinder under a light load. Also, observethe pressure readings on Gauges A, B, and C. This is the data forthe light load row of the chart.

Notice how the increased load affects the cylinder’s speed when itis being controlled by a standard flow control valve.

You should observe that the time to extend is greater even thoughthe flow control valve’s setting is the same. This is because thehigher load pressure is causing more flow to be diverted across therelief valve.

q12. Repeat step 10 to change the load on the cylinder to approximately 250 psi/1725 kPa. This is a heavy load.

q13. Extend the cylinder under a heavy load and measure the time toextend and the pressure gauge readings. Record your data in theheavy load row of the chart.

You should observe that the cylinder slows down even further.

q14. Leave the cylinder retracted, reduce the relief valve setting to itsminimum, turn off the power unit and close the shutoff valve.

q15. Remove all load from the cylinder rod by turning the adjustmentscrews on the load device CCW.





1. The flow control valve is a(n) ________ valve and a(n)_________ valve in one body.

2. To decrease flow through a flow control valve, turn theadjuster in the _______ direction.

3. In a circuit where a flow control valve controls cylinderspeed, a drop in the load will cause the cylinder to ________ speed.

4. As controlled flow through a flow control valve increases,flow through the _________valve decreases.

5. Fluid entering the flow control valve in the __________flow direction can flow two ways.

SEGMENT 4

METER-IN AND METER-OUT CIRCUITS

OBJECTIVE 10 DESCRIBE THE OPERATION OF A METER-INFLOW CONTROL CIRCUIT AND GIVE AN APPLICATION

This unit has discussed the operation of the needle valve and theflow control valve without concern to the placement in the circuit. Although these valves can be placed at either the inlet or the outlet of the actuator to control actuator speed, the placement of these valves isimportant in some applications.

If the flow control valve is placed at the inlet to the actuator, this iscalled a meter-in flow control circuit, as shown in figure 28. In thisexample, the circuit affects the speed of the cylinder while it extends.The fluid leaving the other end of the cylinder is allowed to leaveunrestricted.


RODEXTENDING

DCVSHIFTED

M

Figure 28. Metering-In to Control Cylinder Extend Speed

The meter-in flow control circuit can also be used to control thespeed of the actuator during retraction, as shown in figure 29.

The meter-in circuit provides precise control and is a commonmethod of controlling speed. However, it cannot be used in allapplications. It can only be used to control speeds where the loadopposes the rod movement. Extending the lift cylinder of a crane, asshown is figure 30, is an example of an opposing load.


RODRETRACTING

DCVSHIFTED

M

Figure 29. Metering-In to Control Cylinder Retract Speed

CRANE FORCESALWAYS ACT

IN THISDIRECTION

LIFT CYLINDER

Figure 30. Hydraulic Lift Crane

In some applications, the load helps the rod movement in onedirection. Retracting the crane’s lift cylinder is an example where theload helps or aids the movement. The meter-in circuit will not work tocontrol speed in these applications because the force of the load will tend to make the cylinder movement "run away."

The meter-in circuit is not normally used with hydraulic motorsbecause almost all motors have an overrunning (aiding) load.

SKILL 4 CONNECT AND OPERATE A METER-INFLOW CONTROL CIRCUIT

q 1. Connect the meter-in flow control circuit shown in figure 31using the large bore cylinder.

If installed, remove the load spring.

In this circuit, Gauges A and B indicate the pressure drop acrossthe flow control valve. The flowmeter will measure the flowthrough the flow control valve.



to meter in the flow and demonstrate the operation of thiscircuit.

SUPPLYMANIFOLD

RETURNMANIFOLD

DIRECTIONALCONTROL

VALVE

GAUGEB

GAUGEA

LARGEBORE

CYLINDERCONNECT TEE'SAT THE FLOW CONTROL VALVE

TEE

TEE

A

B

FLOWCONTROL

VALVE

IN

OUT

A

BIN OUT

FLOWMETER

GAUGEC

Figure 31. Schematic of a Meter-In Flow Control Circuit


q 3. Perform the following substeps to set up the circuit for testing.A. Close the flow control valve completely and then open it 1/2

turn. This will cause the cylinder extend speed to slow,allowing extend times to be easily measured.

B. Turn on the hydraulic power unit.C. Increase the relief valve setting until Gauge S reads 400

psi/2760 kPa.D. Open the shutoff valve.

You are now ready to operate the meter-in circuit.q 4. Extend the cylinder and observe the operation of the cylinder using

a meter-in flow control circuit.

You should observe that the cylinder extends at less than fullspeed.

q 5. Once the cylinder is fully extended, retract the cylinder andobserve the speed of retraction.

You should observe a rapid retraction because flow bypassesthrough the check valve.

q 6. Perform the following substeps to see how slowly you can get thecylinder to extend.A. Close the flow control valve enough to obtain a slow, smooth

speed.

You should observe that very slow and smooth cylinderextension is easily obtained. This would not be the case if using pneumatics. This is one of the most important features of ahydraulic system.

B. Record the slowest extend time obtained.

Time to Extend ______________________________(Seconds)

70 to 90 seconds is typical.q 7. Perform the following substeps to experiment with your ability to

control cylinder speed with a meter-in flow control circuit.A. Adjust the flow control valve so that the flowmeter reads 0.5

gpm/1.9 lpm while the cylinder is extending.To do this, you will have to make several trial adjustments tothe flow control valve’s setting. Cycle the cylinder after eachadjustment to observe the flowmeter reading.


NOTEYou may have to extend and retract the cylinder several times

to get the slowest setting.

B. Once the flow rate is adjusted, extend the cylinder again andrecord in the following table the time required to extend. Also,record the maximum readings of Gauges A, B, and C while thecylinder is extending. You should observe that Gauge A indicates a pressure close to400 psi/2760 kPa because the rest of the pump flow is goingthrough the relief valve. The pressures at Gauges B and Cshould be low because there is no load on the cylinder and theoil leaves the cylinder unrestricted.

C. Observe the flowmeter and Gauge C as you retract the cylinder. Full pump flow should be going to the cylinder and oil leavingthe cylinder flows through the bypass check valve of the flowcontrol valve unrestricted.You should observe low pressure on Gauge C.

D. Repeat substeps A, B, and C for each of the other flow rateslisted in the chart.You should observe a decrease in extend stroke time as flowrate to the cylinder increases. Pressure gauge readings shouldremain nearly the same.This exercise shows that you can precisely adjust the speed ofthe cylinder using meter-in speed control.

q 8. Reduce the relief valve to its minimum setting.


NOTERead the pressure gauges as accurately as possible.


to obtain each of the readings.

METER-IN

FLOWRATE

(gpm/lpm)

EXTENSIONSTROKE

TIME(seconds)

PRESSUREGAUGE A

(psi/kPa)

PRESSUREGAUGE B

(psi/kPa)

PRESSUREGAUGE C

(psi/kPa)

0.5/1.9 / / /

0.75/2.9 / / /

1.0/3.8 / / /

1.25/4.8 / / /

q 9. Install the load spring as shown in figure 32. The load spring willbe placed behind the rod cam so that it simulates the effect of anaiding load during cylinder extend.

q10. Close the flow control completely and then open it 1/4 turn.

q11. Increase the relief valve setting until Gauge S reaches 300 psi /2070 kPa.

You are now ready to observe the operation of a meter-in circuit to control the speed of an aiding or overrunning load.

q12. Retract and then extend the cylinder to observe its operation usinga meter-in flow control circuit.

You should observe that the cylinder rod jumps suddenly when the DCV is shifted.

q13. Repeat step 12 several times to observe the operation of a meter-incircuit with an over-running load. Try several different flowcontrol settings to see if this has any effect.

You should observe that the meter-in circuit does not provide good speed control to a cylinder with an over-running load.

q14. Close the shutoff valve, reduce the relief valve to its minimumsetting, and turn off the hydraulic power unit.


NOTEThe instructions for installing the load spring are given in LAP

3 (Skill 4).

SUPPLYMANIFOLD

RETURNMANIFOLD

DIRECTIONALCONTROL

VALVE

GAUGEB

GAUGEA

LARGEBORE

CYLINDERCONNECT TEESAT THE FLOW CONTROL VALVE

TEE

TEE

A

B

FLOWCONTROL

VALVE

IN

OUT

A

BIN OUT

FLOWMETER

GAUGEC

LOADSPRING

Figure 32. Schematic of Circuit with an Aiding Load During Extend

q15. Move the handle of the DCV back and forth to remove anypressure still in the circuit.

Leave the load spring installed on the cylinder. It will be used inthe next skill.

OBJECTIVE 11 DESCRIBE THE OPERATION OF A METER-OUTFLOW CONTROL CIRCUIT AND GIVE AN APPLICATION

Another method of controlling flow rate is a meter-out flow controlcircuit. This type, shown with a cylinder in figures 33 and 34, controlsspeed by restricting the flow of oil leaving the actuator. The fluidentering the actuator enters unrestricted.

Meter-out circuits control actuator speed well when the load is either aiding or opposing. This makes the meter-out circuit a more versatilemethod than the meter-in circuit.

The meter-out circuit is able to control speed when the load tends torun away (aiding loads) because it creates a back pressure on theactuator. This back pressure is able to resist the force of the load. Thisback pressure also creates an opposing load at the cylinder or motor tokeep the actuator in control with a solid cushion of fluid. Most fluidmeter circuits use meter-out flow control.


RODEXTENDING

DCVSHIFTED

M

Figure 33. Metering Out to Control Cylinder Extend Speed

SKILL 5 CONNECT AND OPERATE A METER-OUTFLOW CONTROL CIRCUIT

q 1. If not already installed, mount the load spring behind the rod camand set up the meter-out flow control circuit shown in figure 35.

In this circuit, the flow control valve will control the flow rate only when the cylinder extends. Gauges A and B indicate the pressuredrop across the valve. The flowmeter indicates the flow rate to thecylinder. The load spring provides an aiding load during extension.


RODRETRACTING

DCVSHIFTED

Figure 34. Metering Out to Control Cylinder Retract Speed


in a meter-out flow control circuit and demonstrate theoperation of this circuit when the load is aiding.


q 3. Perform the following substeps with the hydraulic supply.A. Turn on the hydraulic power unit.B. Adjust the relief valve pressure to 300 psi/2070 kPa.C. Open the shutoff valve.

q 4. Close the flow valve completely and then open it 1/2 turn. Thiswill cause the cylinder speed to be reduced.

q 5. Extend the cylinder and observe its operation using a meter-outflow control circuit with an aiding load.

Observe if the cylinder rod jumps suddenly when the DCV isshifted or if the movement is smooth and controlled.

You should observe that rod movement is smooth, controlled andextends at less than full speed. This shows how a meter-out circuitis better for overrunning loads than a meter-in circuit.

q 6. Once the cylinder is fully extended, retract the cylinder. Observecylinder speed. Is it still controlled by the flow control valve ordoes it bypass through the check valve?

You should observe that it partially retracts at full speed.

q 7. Repeat steps 5 and 6 several times to observe the operation of ameter-out circuit with an aiding load. Try several different flowcontrol settings to see if this has any effect.

You should observe that cylinder extension is smooth andcontrolled.


SUPPLYMANIFOLD

RETURNMANIFOLD

GAUGE AGAUGE B

LARGEBORE

CYLINDERCONNECT TEESAT THE FLOW CONTROL VALVE

TEE TEEB A

FLOWCONTROL

VALVEIN

OUT

A

BIN OUT

FLOWMETER

LOADSPRING

Figure 35. Schematic of Meter-Out to Extend Flow Control Circuit

q 8. Reduce the relief valve pressure to minimum, close the shutoffvalve, and remove the load spring.

q 9. Increase the relief valve pressure until Gauge S reads 400 psi /2760 kPa.

q10. Perform the following substeps to see how slowly you can get thecylinder to extend.A. Open the shutoff valve.B. Close the control valve enough to obtain the slowest, smoothest

speed.

C. Record the slowest extend time obtained.

Time to Extend ______________________________(Seconds)

70 to 90 seconds is typical.

q11. Perform the following substeps to experiment with your ability toset specific cylinder speeds with a meter-out circuit.A. Adjust the flow control valve so that the flowmeter reads 0.5

gpm / 1.9 lpm while the cylinder is extending. To do this, youwill have to make several trial adjustments to the flow controlvalve’s setting. Cycle the cylinder after each adjustment toobserve the extend time.

B. Once the flow is adjusted, extend the cylinder again and recordthe time required to extend in the table. Also, record thereadings of Gauges A, B, and S while the cylinder is extending.

You should observe that Gauges A and S read near 400psi/2760 kPa because the rest of pump flow is going over therelief valve gauge. Gauge B should be minimum becauseduring extend it is indicating return pressure.


NOTEYou should observe that very slow and smooth cylinder

extension is easily obtained. This would not be the case if usingpneumatics.


to obtain the readings.

NOTERecord the pressure gauge readings as accurately as possible.

C. Retract the cylinder while observing the cylinder speed,flowmeter indication and Gauge A reading.The cylinder rod should retract rapidly, because the pump flowis going across the bypass check to the cylinder. Gauge Ashould be at a low pressure.

D. Repeat substeps A, B, and C for each of the other flow rateslisted in the chart. You should observe a decrease in extend time as flow rate tothe cylinder increases. Pressures should remain close to thoseobtained in substeps B and C.The stroke times obtained should be nearly the same as thoseobtained with the meter-in circuit.

q12. Reduce the relief valve to its minimum setting, close the shutoffvalve, and turn off the power unit.



METER-OUT

FLOWRATE

(gpm/lpm)

EXTENSIONSTROKE

TIME(seconds)

PRESSUREGAUGE A

(psi/kPa)

PRESSUREGAUGE B

(psi/kPa)

PRESSUREGAUGE S

(psi/kPa)

0.5/1.9 / / /

0.75/2.9 / / /

1.0/3.8 / / /

1.25/4.8 / / /



1. ________ flow control circuits are used when the load isaiding or over-running.

2. Either a meter-in or meter-out flow control circuit may beused when the load is ________________.

3. Meter-out circuits control actuator speed well when the loadis either _________ or opposing.

4. A meter-in flow control circuit controls speed by controllingthe amount of oil going ________________ the actuator.

5. The meter-in circuit provides precise control and is acommon method of controlling __________.

6. Most motor speed circuits are meter-out because almost allmotors have ________________ loads.

SEGMENT 5

FLOW CONTROL CIRCUIT DESIGN

OBJECTIVE 12 DEFINE INDEPENDENT SPEED CONTROLAND GIVE AN APPLICATION

In most cases, an industrial actuator’s speed in each direction mustbe adjusted independently of each other. This is called independentspeed control. The reasons for this include:

• Slow Approach / Fast Reset - Machines often require a cylinder toextend very slowly while it is performing an action. If the retractstroke is used only to reset the cylinder for the next cycle, it isdesirable to retract at high speed to cut the cycle time.An example is the metal expander machine shown in figure 36. Thismachine requires the cylinders to slowly extend while they areexpanding the metal tube. The cylinder can retract at high speed toreset for the next part.

• Identical Speeds - Because the rod and cap end areas of a cylinder aredifferent, a cylinder will naturally extend and retract at differentspeeds because the flow rate to the cylinder is the same duringretraction and extension.


Figure 36. Metal Expander Machine with Slow Approach/Fast Reset

Independent speed control requires two flow control valves. Onevalve controls the speed in each direction. These valves can be connected to provide either meter-in or meter-out speed control.

SKILL 6 DESIGN AN INDEPENDENT SPEED CONTROL CIRCUIT

q 1. Complete the circuit shown in figure 37 so that you can control the speed of the cylinder in each direction using a separate flowcontrol valve. Draw the two flow control valves so that each valveprovides meter-out flow control.

Label your flow control valves FC1 and FC2. FC1 should controlthe extend speed and FC2 should control the retract speed.

q 2. Connect your circuit design on the 850 Series trainer.


Procedure OverviewIn this procedure, you will design a circuit that will

separately control the speed of an actuator in eachdirection.

SUPPLYMANIFOLD

RETURNMANIFOLD

LARGEBORE

CYLINDER

IN

OUT

A

B

DIRECTIONALCONTROL

VALVE

Figure 37. Partial Schematic


q 4. Perform the following substeps to set up the circuit for testing.A. Close both flow control valves completely. Then open each 1/2

turn. This will cause the speed of the cylinder to be slow forboth directions of motion.

B. Turn on the hydraulic power unit.C. Adjust the relief valve pressure to 400 psi / 2760 kPa.D. Open the shutoff valve.

You are now ready to demonstrate independent speed control.q 5. Extend and retract the cylinder. Notice whether the speed is

controlled in both directions.

You should observe that the speed is controlled in both directions.

Confirm your design with the data sheet solution. This is a classiccircuit design that designers often use in hydraulic circuits.

q 6. Adjust FC 1 to several different settings to test its effect on thecircuit. Extend and retract the cylinder after each new adjustmentand observe the cylinder’s speed.

You should observe that the speed of the cylinder changes for only one direction of motion when FC 1 is readjusted. Record belowwhich direction of motion changes.

FC 1 controls _____________________________(Retract/Extend)

You should observe that only the extend speed is affected.

q 7. Reset FC 1 to 1/2 turn open.

q 8. Now adjust FC 2 to several different settings to test its effect onthe circuit. Extend and retract the cylinder after each newadjustment and observe the cylinder’s speed.

You should observe that the speed of the cylinder changes for only one direction of motion when FC 2 is readjusted. This should bethe direction opposite that of FC 1. Record below this direction.


q 9. Reduce the relief valve pressure to minimum, close the shutoffvalve and turn off the power unit.


q11. Now design and connect a new circuit that performs the same taskas your circuit in figure 37 except that it uses meter-in speedcontrol.


q12. Perform the following substeps to set up the circuit for testing.A. Close both flow control valves completely. Then open each 1/2

turn. This will cause the speed of the cylinder to be slow forboth directions of motion.

B. Turn on the hydraulic power unit.C. Adjust the relief valve pressure to 400 psi/2760 kPa.D. Open the shutoff valve.

You are now ready to demonstrate independent speed control.q13. Extend and retract the cylinder. Notice whether the speed is

controlled in both directions.

You should observe that the speed is controlled in both directions.

Confirm your design with the data sheet solution. The circuit isalso a classic design that you often see.

q14. Adjust FC 1 to several different settings to test its effect on thecircuit. Extend and retract the cylinder after each new adjustmentand observe the cylinder’s speed.

You should observe that the speed of the cylinder changes for only one direction of motion when FC 1 is readjusted. Record belowwhich direction of motion changes.


You should observe that only the extend speed is affected.

q15. Reset FC 1 to 1/2 turn open.

q16. Now adjust FC 2 to several different settings to test its effect onthe circuit. Extend and retract the cylinder after each newadjustment and observe the cylinder’s speed.

You should observe that the speed of the cylinder changes for only one direction of motion when FC 2 is readjusted. This should bethe direction opposite that of FC 1. Record below this direction.


q17. Reduce the relief valve pressure to minimum, close the shutoffvalve and turn off the power unit.



OBJECTIVE 13 EXPLAIN HOW SPEED CONTROL VALVES CAN BE USEDTO PROVIDE MULTIPLE SPEEDS

In some applications, there is a need to have an actuator operate atdifferent speeds. An example of this is the rapid approach of a machinetool to get it into position followed by a slow feed while machining. This is called a rapid traverse-slow feed. This technique helps increase theproductivity of the machine.

An easy method of providing multiple actuator speeds is to use aseparate speed control valve for each speed and switch to the flowcontrol valve (speed) desired. This switching is done using a DCV.


Figure 38. Hydraulic Press with Rapid Traverse-Slow Feed

SKILL 7 DESIGN A TWO-SPEED ACTUATOR CIRCUIT

q 1. Complete the design of the circuit shown in figure 39 to providetwo-speed control of the motor.

With the DCV in neutral (not shifted), the motor should be already running at a speed that can be adjusted. This is to be the low speed part of the circuit.

When the DCV is shifted to the straight arrows condition, themotor should continue to run but at a higher speed. This higherspeed should also be adjustable.

Label the low speed flow control valve as FC1 and the high speedflow control valve as FC2.

q 2. Set up your circuit on the trainer.

q 3. Perform the following substeps to set the speed controls.A. Close FC1 completely and then open it 1/2 turn.B. Close FC2 completely and then open it two turns.


Procedure OverviewIn this procedure, you will design a circuit to provide

two speeds to an actuator as it operates in one direction.

SUPPLYMANIFOLD

RETURNMANIFOLD

IN

OUT

A

B

INOUT

FLOWMETER

MOTOR DCV

Figure 39. Partial Schematic of a 2-Speed Motor Circuit


q 5. Perform the following substeps with the hydraulic supply.A. Turn on the hydraulic power unit.B. Adjust the relief valve pressure to 400 psi / 2760 kPa.C. Open the shutoff valve.The motor should start and run at low speed.

q 6. Now push in on the handle of the DCV and observe the speed ofthe motor.

You should observe the motor running fast.

q 7. Release the handle of the DCV.

The motor should return to its slow speed.

q 8. Reduce the relief valve to its minimum setting, turn off the powerunit, and close the shutoff valve.




1. The __________ speed control circuit uses separate flowcontrol valves to control the speed of an actuator in bothdirections.

2. Multiple speed circuits may use flow control valves and__________ to switch between them.

3. A rapid traverse-slow feed circuit is used to increasemachine ________________.

4. Because the _____ and _____ end areas are different in adouble-acting cylinder, extend and retract times aredifferent.

5. Retract stroke on a double-acting cylinder is done at highspeed when it is used to _______________ the cylinder forthe next cycle.

SEGMENT 6

FLOW RATE VS. CYLINDER SPEED

OBJECTIVE 14 DESCRIBE HOW TO CALCULATE THE EXTEND SPEEDOF A HYDRAULIC CYLINDER

The speed of a cylinder depends only on the entering flow rate andthe volume being filled. Therefore, in order to calculate the extend speed, it is necessary to recognize that the oil flow is causing the piston to bemoved and creating a greater volume inside the cap end of the cylinder.The rate at which the piston moves depends on the rate at which the flow of oil can fill the volume of the cap end of the cylinder. The rod speed(RS) extending is therefore the rate at which the cylinder’s volume isfilled as shown in figure 40. This calculation is made using the following formula:


FORMULA: EXTEND SPEED OF A CYLINDER

Rod SpeedFlow Rate

Area=

U.S. Customary Units:

Extend Rod Speed (in/min) = Flow Rate gpm

Piston Area in

( )

( )

× 2312

S.I. Units:

Extend Rod Speed (cm/min) = Flow Rate lpm

Piston Area cm

( )

( )

×10002

SKILL 8 CALCULATE THE EXTEND SPEED OF A HYDRAULICCYLINDER GIVEN ITS SIZE AND A FLOW RATE

q 1. Calculate the piston areas of the two cylinders on the Amatroltrainer given the following information:

The piston diameter of the large bore cylinder is 1.5 in (3.81 cm)and the piston diameter of the small bore cylinder is 1.125 in. (2.86 cm).

The formula for the area of a circle is: A = 0.7854 (D2) where D isthe bore diameter.

Large Bore Cylinder Piston Area =__________________ (in2/cm2)

Small Bore Cylinder Piston Area =__________________ (in2/cm2)


R

FLOWVOLUME = R x A

RATE OF VOLUME INCREASE = (RS) x A

WHERE A = AREA OF PISTON

R = LENGTH OF VOLUMEIN CAP END

A

EXTENDSPEED (RS)

RS = ROD SPEED

Figure 40. Calculating Extend Speed of a Cylinder

Procedure OverviewIn this procedure, you will calculate the extend speeds

of the cylinders used in the 850 Series trainer for severalflow rates as well as determine what cylinder size isneeded to produce extend speeds when given the flowavailable.

q 2. Using the areas from step 1, calculate the extend speeds of the twocylinders for each of the flow rates shown in the table. Use theformula for the extend speed of a cylinder.

q 3. Determine the size of a cylinder given the following information:

Extend Rod Speed = 74 in/min / 188 cm/min

Flow rate available = 4 gpm/15.2 lpm

Choose a size to the nearest inch or centimeter. Show your work.

Cylinder Bore Diameter ____________________________(in/cm)

Your calculations should produce a 4 in/10 cm bore diameter.

q 4. Determine the flowrate needed to extend a cylinder at a speed of12 in/min / 30.5 cm/min. The cylinder’s bore size is 6 in / 15.2 cm. Show your work.

Flowrate Needed = _____________________________(gpm/lpm)

Your calculations should produce a required flow rate of 1.47gpm/5.53 lpm.

q 5. You are an engineer who is assigned to specify the size of ahydraulic cylinder for a project. Determine the cylinder’s bore size and the maximum force output of the cylinder given the followinginformation:

Flowrate available = 26 gpm / 99 lpm.

Extend speed required = 300 in/min / 762 cm/min.

Pressure available = 1500 psi/10,350 kPa.

Specify the cylinder’s bore diameter to the nearest inch andcentimeter. Show your work.


Your calculations should produce a 5 in / 13 cm bore diameter.

Calculate the maximum force output of the cylinder.

Maximum Force Output ____________________________(lbs/N)

Your answer should be 29,453 lbs / 137,378 N.


FLOWRATE

(gpm/lpm)

EXTEND SPEED

LARGE BORECYLINDER

(in/min) / (cm/min)

SMALL BORECYLINDER

(in/min) / (cm/min)

0.5/1.9 / /

0.75/2.9 / /

1.0/3.8 / /

1.25/4.8 / /

OBJECTIVE 15 DESCRIBE HOW TO CALCULATE THE RETRACT SPEEDOF A CYLINDER

The retract speed of a double-acting cylinder is different than theextend speed because there is less volume to fill. With the rod attached to the piston, only the annular area need be considered. This means that fora given flow rate, a cylinder will retract faster than it extends. Theformula to calculate the retract speed is as follows:


FORMULA: RETRACT SPEED OF A CYLINDER

Rod SpeedFlow Rate

Area=


Retract Rod Speed (in/min) = Flow Rate gpm

Annular Area in

( )

( )

× 2312

S.I. Units:

Retract Rod Speed (cm/min) = Flow Rate lpm

Annular Area cm

( )

( )

×10002

SKILL 9 CALCULATE THE RETRACT SPEED OF A CYLINDERGIVEN ITS SIZE AND A FLOW RATE

q 1. Calculate the annular area of each cylinder given the followinginformation:

The large bore cylinder has a piston diameter of 1.5 in. (3.81 cm)and a rod diameter of 0.44 in. (1.12 cm). The small bore cylinderhas a piston diameter of 1.125 in. (2.86 cm) and a rod diameter of0.31 in. (0.79 cm).

Large Bore Cylinder Annular Area__________________ (in2/cm2)

Small Bore Cylinder Annular Area__________________ (in2/cm2)

q 2. Using the areas from step 1, calculate the retract speeds of the twocylinders for each of the flow rates shown in the table. Use theformula for the retract speed of a cylinder.


Procedure OverviewIn this procedure, you will calculate the retract speeds

of the cylinders on the hydraulic actuator module andperform other calculations based on retract speeds.

FLOWRATE

(gpm/lpm)

RETRACT SPEED

LARGE BORECYLINDER

(in/min) / (cm/min)

SMALL BORECYLINDER

(in/min) / (cm/min)

0.5/1.9 / /

0.75/2.9 / /

1.0/3.8 / /

1.25/4.8 / /

q 3. Compare these speeds with those calculated earlier for extend.

You should observe that for the same flow rates, speed ofretraction is faster than the speed of extension. This occurs because there is less volume to fill during retract.

q 4. Determine the size of a cylinder given the following information:

Retract Rod Speed = 110 in/min / 279 cm/min.

Rod Diameter = 1 in / 2.54 cm.

Flow rate available = 3 gpm / 11.4 lpm.

Choose a size to the nearest inch or centimeter. Show your work.


Your calculations should produce a 3 in / 7.6 cm bore diameter.

q 5. Determine the flowrate needed to retract a cylinder at a speed of 30 in/min / 76 cm/min.

The cylinder’s bore size is 6 in/15 cm.

The cylinder’s rod size is 1.15 in / 3.8 cm. Show your work.

Flowrate needed _______________________________(gpm/lpm)

Your calculations should produce a flowrate of 3.44 gpm / 12.57lpm.


NOTEBe sure you adjust your calculation to account for the area of

the rod. The diameter you will need to specify is the pistondiameter for the cylinder.

OBJECTIVE 16 DESCRIBE HOW TO CALCULATE THE STROKE TIMEOF A CYLINDER

In many applications you may want to know the amount of timerequired for a particular cylinder to complete its stroke given a flow rate.This calculation is a variation of the rod speed calculation. It is theformula for rod speed divided into the total stroke length as follows:

Cylinder Stroke TimeStroke Length

Rod Speed=

Since rod speed is equal to flow rate ÷ cylinder area, the formula isas follows:


FORMULA: CYLINDER STROKE TIME

Cylinder StrokeTimeArea Stroke

Flow Rate=

×


Stroke Time (sec) = Area in Stroke in

Flow Rate gpm

( ) ( )

( )

2 60

231

× ××

S.I. Units:

Stroke Time (sec) = Area cm Stroke cm

Flow Rate lpm

( ) ( )

( )

2 60

1000

× ××

NOTEWhere area is either the piston area for extend or the annular

area for retract.

SKILL 10 CALCULATE THE CYLINDER STROKE TIMEGIVEN ITS SIZE AND A FLOW RATE

q 1. Using the areas calculated previously, calculate the extend stroketimes of the two 850 Series cylinders for each of the flow ratesshown in the following table. Use the formula for cylinder stroketime.

The stroke of the large bore cylinder is 4.0 in (10.2 cm) and thestroke of the small bore cylinder is 6.0 in (15.2 cm).


Procedure OverviewIn this procedure, you will be using the 850 Series

cylinders again. You will then compare these calculationswith the actual measurements made in Skill 4.

FLOWRATE

(gpm/lpm)

EXTEND STROKE TIME

LARGE BORECYLINDER(seconds)

SMALL BORECYLINDER(seconds)

0.5/1.9

0.75/2.9

1.0/3.8

1.25/4.8

FLOWRATE

(gpm/lpm)

RETRACT STROKE TIME

LARGE BORECYLINDER(seconds)

SMALL BORECYLINDER(seconds)

0.5/1.9

0.75/2.9

1.0/3.8

1.25/4.8

q 2. Now calculate the retract stroke times for the two cylinders foreach of the flow rates shown in the table. Use the formula forcylinder stroke time.

q 3. Compare the retract and extend stroke times.

_____________________________________________________

_____________________________________________________

You should observe that at the same flow rates, retract stroke times are shorter than extend stroke times.

q 4. Now compare the large bore cylinder calculated stroke timesduring extend with those obtained in skill 4. Are they reasonablyclose?

______________________________________________(Yes/No)

You may find the stroke times obtained in Skill 4 quite differentthan the calculated values because of timing and flow meterinaccuracies. Generally they should agree.




1. To calculate the annular area of a cylinder you must knowthe piston and _______________ diameters.

2. The extend speed of a cylinder depends on the entering flowrate and the _______________ being filled.

3. For a given flow rate, a double-acting cylinder will retract_______________ than it extends.

4. To calculate cylinder stroke time, you need to know pistonarea, flow rate, and stroke _______________.

5. For a given flow rate, increasing the cylinder rod diameterwill __________ retraction speed.

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