BASIC Hydraulic-kapil

OH043.1Internal Use Only

Basic Logging Truck Hydraulics


Basic Logging Truck HYDRAULICS

As a logging engineer you wil l have to run the Winch sometime

This basic course wil l help you understand why and how of the Truck Hydraulics


Why Hydraulics• Transmission of power is very easy and f lexible

using Hydraulics. Pumps and Motors are connected by f lexible hoses

• It is safe in the sense that it does not have f ire or electr ical hazards. Remember we need to switch OFF / Disconnect the Truck Alternator during Explosive related operations yet the Winch has to move. Hydraulics can be run from the Truck 12 V Battery

• It is relat ively maintenance free. Just keep changing Oil & Filters regularly as scheduled in PM manuals

• Hydraulic operations are smooth and noiseless.• The ease with which one can control Speed, Torque,

Direction of the winch by operating just one Joy Stick


Hydrostatic laws• I f pressure is applied

on surface of the same area, the forces which are produced are the same size.

• Forces depend on height of l iquid not on the shape of the container in which l iquid is placed.

• Hydrostatic laws assume an ideal f luid which is incompressible, fr ict ionless and without mass.


Pascal’s law• The effect of a force

acting on a stationery l iquid spreads in all directions within a l iquid.

• The amount of pressure in the liquid is the equal to the weight force, with respect to the area being acted upon.

• The pressure always acts at right angles to the l imiting surface of the container.


Pressure due to external force

• P = F1/A1• F2 = P.A2• F1/A1 = F2/A2• As such a small force

applied on the small area side can result in much larger force on a large area.


Important characteristics of hydraulic circuits• Transfer of large forces• Operations may commence from rest under ful l load.• Smooth adjustments of the following is easily

achieved:• Speed• Torque• Force• Change of Direction (no engaging reverse gear)

• Simple protection against overloading.• Suitable for both quick and very slow controlled

sequence of movements.• Decentralized transformation of mechanical/electrical

to hydraulic and hydraulic to mechanical energy is possible


Logging Truck hydraulics

There are 2 Independent* Closed Loop Hydraulic circuits in a Logging Truck (or Skid)

* These two independent circuits share a common Prime Mover and a common Hydraulics oil tank

1.Controls direction, Speed and Torque of the Winch

2.Runs the Alternator at a constant speed of 1800 rpm under changing load conditions


Closed Loop Hydraulic circuit- Electrical analogy

Current source

A

VR

I

V= IR , I = V/R

Power = V * I

The current source feeds power while the Resistor dissipates Power

Pressure = Flow*Load

Power = Pressure * Flow , Torque * RPM

The Pump converts mechanical energy to hydraulic energy while the Motor converts hydraulic energy back to mechanical energy


Closed Loop Hydraulic circuit components

Prime Mover (M) Source - Truck/Skid Diesel Engine

Hydraulic Pump (2)

Hydraulic Fluid (1)

Hydraulic Motor (4)

Various accessories l ike Hoses, Filters, Controls, Valves etc.

Pump Motor

Pressure Gauge

Fluid FlowMechanical energy turns the Pump, which sucks hydraulic fluid from a tank and pushes it out under pressure. The pressurized fluid is taken to the motor in a hose. The pressurized fluid turns the motor, looses energy and returns to tank


Well, It’s not that simple

Pump Motor

Pressure Gauge

Fluid Flow

What wil l happen if

1. The load on the motor increases

2. How to stop the motor without stopping the engine

3. The Hydraulic oil heats up, gets dirty with metal dust

1. If the load on the motor increases, pressure wil l increase. It may burst the hoses, stall the pump and engine, cause mechanical damage

2. Variable Displacement is the answer

3. When hydraulic oil heats up, it might loose its properties and start burning, spoil the rubber seals and gaskets. Metal dust has to be fi l tered


Case 1 – Safety from High Pressure

A simple relief valve may consist of nothing but a ball or poppet held seated in the valve body by the compressive force of a heavy spring. When the pressure at the inlet is insuff ic ient to overcome the force of the spring the valve remains closed and hence i t is very often referred as a normally closed valve. When the preset pressure is reached, the ball unseats and al lows f low through the outlet to tank. In most of these valves, an adjusting screw is provided to vary the spring force. Thus the valve can be set to open at any pressure within the specif ied range. The pressure at which the valve f irst opens is called the cracking pressure. A relief valve should NOT be allowed to operate in Rel ief mode for long.

Relief Valve – Operates much l ike a Zener Diode

Pump Motor

Pressure Gauge

Fluid Flow


Case 2 – Displacement (just like Gears)

Displacement of a Pump (or Motor) is the amount of f luid moved per Rotation. Displacement is measured in cc. For example a Pump could be 90cc (meaning that for each complete rotation of the Pump shaft 90cc of

oil wil l come out) and a Motor could be 120cc.

Pump Motor

Pressure Gauge

Fluid Flow

In our example let

Pump = 90 cc

Motor = 120 cc

If the engine rpm (ω 1) is 1200 then what is the rpm of the motor (ω2)?


Case 2 – Variable DisplacementThink of Variable Displacement as being able to adjust the angle of a Fan’s blades. If we make the Blades FLAT (angle=0) then even if the Fan rotates no flow wil l take place.

What wil l happen if the angle is revered?In a Logging Truck, we use Variable Displacement Pumps

Pump 0-90 Motor

Pressure Gauge

Fluid Flow


Case 2 – Changing Direction of the motor•To change the direction of rotation of the motor the Fluid f low

direction MUST change to reverse. Fluid Flow direction is controlled by Pumps

•Fluid Flow direction can be changed smoothly by Axial Piston design Variable Displacement Pumps that can achieve this even while turning in the same direction at the same rpm (much l ike the Fan example of last sl ide)

The Displacement of the Pumps (or motors) can be controlled by a simple Electrical Joystick Lever.

In Logging Trucks/Skids the Winchman’s Joystick sends a DC Current to Solenoid coils mounted on the Hydraul ic Pump.


Case 2 – Over center Variable Displacement Pumps

Axial Piston Variable Displacement Pumps can also change the direction of Fluid Flow. Such pumps are called Over-center pumps

This means on such Pumps there is NO HIGH pressure Port and NO LOW pressure port. Instead there are 2 ports (A and B) when one is HIGH the other is LOW.

Notice that Motors can be variable displacement too but displacement can never be zero (or close to zero). Why?


Case 3 – Cooling and Filtration of Hydraulic Fluid

As both ports (A & B) can be HI pressure (though not at the same time), we must create a separate Port (C) where pressure wil l always be LOW. This port is called CASE DRAIN. Some portion of the oi l is intentionally leaked out of the main circuit, collected and sent back into a Tank. But before it reaches the Tank we cool i t in a radiator.

A

B B

A

C C


Case 3 – Cooling and Filtration As we have removed some Oil, we must replenish the same, else the hydraulic circuit wil l soon starve. This is done by a separate pump called Charge Pump and a Charge circuit.

A Charge Pump sucks CLEAN, COOLED, FILTERED Oil from the tank and pushes it back into the main circuit by injecting oil in the low pressure side.


Hydraulics so far….• Logging Hydraulics systems are closed loop

systems.• There are 2 independent systems (Winch,

Alternator)• Pumps used in both these two circuits are Over

center Variable Displacement Axial Type• Controls to the Pump and Motors are electrical

(12V DC)• System pressure is l imited to 5500 psi by relief

valves• Charge Pumps are Gear type pumps that are

mounted along with the main pumps. Since we have 2 main pumps we also have 2 charge pumps

• Hydraulic oil must be f i l tered and cooled


Simple Hydraulics Diagram of Truck/Skid


Advanced Truck HydraulicsIn this section you wil l learn about the practical aspects of the Hydraulics system as used in a Logging Truck or Skid


Lets start with the Engine and PTO

1. Once the Truck is correctly spotted, it is kept at Neutral.

2. Make sure the Drum Brakes are ON and Winch man’s Joystick in Neutral

3. Inside the drivers cabin, engage the PTO. A PTO (Power Take Off) is an auxil iary gearbox, usually much smaller. Depending on the type of PTO, the Truck diesel engine rpm is slowly increased to about 1500 rpm (1200 old)

4. The PTO (when engaged) drives the 2 Hydraulic Pumps (along with their 2 Charge Pumps) via a drive shaft. In most new Hall iburton Trucks the PTO rpm is equal to engine rpm

5. Both Pumps always start at Zero displacement. The Charge pumps builds the system pressure to around 400 psi.


Various Pumps on Halliburton Trucks and Skids1. Over center Variable Displacement 90 cc Axial

Pump for the Winch. Model Rexroth AA4VG90EL

2. Over center Variable Displacement 56 cc Axial Pump for the Alternator. Model Rexroth AA4VG56EL

3. Along with each of the above 2 pumps are 2 Charge Pumps. The Charge Pumps are simple Gear type pumps stuck together along with the main pumps

The entire block of 4 pumps is then made into 1 assembly having a common drive shaft running thru and thru

Cha

rge

Pum

p

Cha

rge

Pum

p


The Charge Pump

A charge pump is a simple gear pump necessary for our system because of the following:

• To supply system with cool fluid• To supply fluid to compensate for

leaks• To keep the system under pressure

As the gears rotate oil is trapped and pushed from one port (Low) to another (High)A Charge Pump wil l NOT work if rotated in the opposite direct ion


The Rexroth AA4VG__EL Axial PumpsBoth the main Pumps (90cc and

56cc) are of similar design called the Axial Piston Pumps

Both the main Pumps are Over center variable displacement type

Both pumps are control led by Electrical 12V DC signals

So how do these pumps work?

Swashplate principle


Swash-Plate principle


Motors used in Halliburton Trucks and Skids

Alternator Motor Rexroth AA2FM32

Fixed Displacement of 32 cc

Winch Motor Rexroth AA6VM80EL

Variable Displacement from 25cc to 80cc.

No signal Default 80cc*Some Skids may have 55 cc motors depending on Planetary Gear-Box

Both Motors are Bent Axis type Axial Piston Motors


The Bent Axis Principle

The Winch Motor displacement depends on the Axis angle can vary from a min to give 25 cc to a max to give 80cc

The Alternator Motor Axis angle is f ixed to give 32 cc displacement

*Decreasing Swivel Angle decreases Displacement (therefore increases RPM) but Hydraulic Motors cannot have 0 cc displacement of as that would mean Infinite RPM and Zero Torque


Hydraulics Diagram of Truck/Skid

Winch Pump Winch Motor

2 Speed Planetary Gearbox

Reel

120V 60Hz Alternator

Variable Displacement 80cc Motor

Fixed Displacement 32cc Motor

Variable Displacement 56cc Pump

Variable Displacement 90cc Pump

Oil Filters Heat exchanger

Case Drain

Diesel

Engine


Mooring Principle (Max Line Tension Control)

• It is basically a l ine tension control valve mounted on the Winch man's control panel.

• In essence it is a system pressure regulator.• The l ine tension valve can also control (and

override the Joy-Stick control) the swash plate angle of Winch pump and when the set pressure is reached it forces the pump to stop pumping in f luid.

• However the set pressure is maintained. • This prevents the cable from breaking accidentally

while the tool is being logged UP (only) and there is a Tight pull.

• On Floaters Mooring Control is a MUST


Mooring Control – How does it work?

Charge pressure l ine


Max Line Tension – Why is it important?

As the Logging Tool goes deeper the Cable weight (and therefore Tension) increases with depth and conversely as the Tool is coming up the Cable weight decreases.

Consider what wil l happen if we were Logging UP and the Tool got stuck (at some deep depth) and the Winch man is NOT paying attention


Requirements of a good hydraulic fluid• Lubrication and anti-wear characteristics• Appropriate viscosity (with respect to pressure)• Stabil i ty against shearing• Stabil i ty against thermal loads• Should have low compressibil i ty ( l i t t le change due to

temperature)• Fire resistant-does not burn• Good protection against corrosion• No formation of sticky substances• Good fi l tration capabil i ty• Cost and availabi l i ty


Review and Questions

• Theory.• Applications• The Hydraulic Circuit• Hydraulic pumps & motors• PM1 issues• Max Line Tension.


Thank You

By- KAPIL DEV

BASIC Hydraulic-kapil

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