EXPRESSOR

By, G.N.Singh,

AP(DSL),IRIMEE

Contents

• Introduction• Requirement of expressor in Diesel Loco• Types Of Expressor• Expressor and its associated components• Maintenance of expressor • Expressor Alignment• To learn the function of exhauster.• To learn the function of compressor.• To learn the loading-unloading arrangement of compressor.• To learn the function of air governor.

Introduction

In ALCO locos the exhauster and the compressor are combined into one unit and is known as Expressor.

It creates 22” of vacuum in the train pipe and 140 PSI air pressure in the reservoir.

It is located at the free end of the engine block and driven through the extension shaft attached to the engine crank shaft coupled together by splined flexible coupling.

Requirement of expressor in Diesel Loco

Trains normally work on vacuum/Air brakes and diesel loco on air brakes therefore provision has been made for both vacuum and compressed air.

Compressed air is required for the working of systems like wiper circuit, horn, control panel etc.

Vacuum/Air is maintained for applying brakes in trains.

So we require a compressor for compressed air and exhauster for generation of required amount of vacuum.

Types of Expressor

There are three types of expressor being used in Indian Railways:

A -- Expressor1. 6CD, 4UC - General2. 6CD, 3UC - KE-6B -- Compressor 3CD-B - KC-523W/623W

6CD 4UC Expressor specific features and data

Details Compressor (LP) Compressor (HP) Exhauster • 1. No. of cylinders 1 1 4 • 2. Cylinder bore 7.750" 4.250" 7.250” • 3. Stroke 5.625" 5.625" 5.265” • 4. Piston rings 2+2 2+2 2+2 (Comp. & oil scrapper)  • 5. Normal working pressure - 140 PSI or 10 Kg/sq cm. • 6. Rated speed - 1000 RPM • 7. Compressor displacement - 153.5 CFM / 4350 LPM at rated speed.

61.4CFM /17400 LPM at rated Idle speed. • 8. Exhauster displacement - 614 CFM / 17400 LPM at rated speed.

246 CFM / 6960 LPM at idling.•  9. H.P consumed - 115 H.P max. • 10. Lube oil pressure - 25 PSI to 60 PSI. • 11. Oil sump capacity – 21/28 Lts. • 12. Weight in assembled condition - 982 Kg.

Components of Expressor

1. Crank case & 2 nos. Crank case cover2. Crank shaft3. Four nos. of exhauster cylinders with cylinder heads.4. One low pressure compressor cylinder (LP) with cylinder head.5. One high pressure cylinder (HP) with cylinder head.6. Six nos. of pistons with piston rings and connecting rods with

bushing at big end & small end and snap ring.7. Lube oil pump , Relief Valve,8. Drive Gear , Sprocket , s-pipe,9. 2 nos. Ball Bearings10. 2 nos. Crank Shaft Oil seal11. Vacuum Maintenance Valve12. Inter cooler13. I/C Safety Valve14. Inlet & Discharge valve15. Gear type & flexible type Coupling

Expressor(6CD 4UC) 6CD means 6 cylinders and 4UC means it has 4

exhauster units. Compressor unit consists of a high pressure (H.P)

cylinder and a low pressure (L.P) cylinder. These are reciprocating type with their pistons

vertical. Also contains intercooler which increases overall

efficiency. The crank shaft is supported at both ends by

double row ball bearings.

Outside the ball bearings, oil seals are located to prevent the leakage of oil from inside the crank case and air from outside into it.

Expressor(6CD 4UC) Assembly

Expressor(6CD 4UC)

Sectional View of Expressor(6CD 4UC)

Expressor(6CD 3UC)

6CD means 6 cylinders and 3UC means it has 3 exhauster units.

All these 3 exhauster units are placed on engine side. The compressor unit is placed on the horizontal shaft side. H.P cylinder is placed in between the two L.P cylinders. Since H.P cylinder has to accommodate incoming

compressed air from two L.P cylinder. Diameter of H.P cylinder is slightly larger than that of H.P

cylinder of 6CD, 4UC. For the same reason capacity of intercooler is also

increased Now, it has more number of fins and volume capacity is

also increased.

Expressor(6CD 3UC)

End View of Expressor(6CD 3UC)

Compressor(3CD-B)

It would not be appropriate to call it an expressor rather it may be called a compressor.

As it doesn’t contain any exhauster unit so vacuum cannot be maintained by this unit.

It consists of two L.P cylinders and one for H.P cylinder.

The outgoing compressed air from L.P cylinder is sent to the intercooler and then the cooled compressed air is passed through H.P cylinder.

The highly pressurized air from H.P cylinder is sent to an after cooler and then to the main reservoirs.

Compressor(3CD-B)

View of Compressor(LG 3CD-B)

Working of Expressor A. Exhauster: Air from vacuum train pipe is drawn into the exhauster

cylinders through the open inlet valves during suction stroke. The pressure differential between the available pressure in

the vacuum train pipe and inside the exhauster cylinder opens the inlet valve and air is drawn into the cylinder from train pipes.

In next stroke the air is compressed and forced through the discharge valve while the inlet valve remains closed.

This process of suction of air from the train pipe continues to create required amount of vacuum and discharge the same to atmosphere. The VA-1 control valve helps in maintaining the vacuum to requisite level despite continues working of the exhauster.

Working of Expressor as Exhauster

Exhaust Pipe

VA1B CONTROL VALVE

VACCUM TRAIN PIPE

EXHAUST VALVE

EXHAUSTERCYLINDER

EXHAUST PIPE

EXHAUST PIPE

INLET VALVE

VACUUM RESERVOIR

INLET VALVE

EXHAUST VALVE

Working of Expressor

B.Compressor: It’s a two stage compressor with one low pressure cylinder and one

high pressure cylinder. The air is sucked from atmosphere through a wire mesh filter and

compressed in the low pressure cylinder. Then it is passed through a radiator known as ‘Intercooler’.

This is an air to air cooler where compressed air passes through the element tubes with attached fins, these are cooled by fan attached to the crank shaft.

Cooled air is then sent to the H.P cylinder. A safety valve known as intercooler safety valve set at 60 psi is

provided after the intercooler as a protection against high pressure developing in the intercooler.

After first stage of compression the air is again compressed in a H.P cylinder to increase the pressure to 135-140 psi.

Air again needs cooling before it is finally sent to the air reservoir and it is done when air passes through a set of coiled tubes below loco superstructure

Expressor work as compressor-

INTER COOLER

MR 1

M R 2

COOLING COIL

Discharge valveL.P H.P

Inlet valve

Inter cooler safety valveJ Filter

Filter cock

Drain cockNRV

HORN

SANDERS

WIPERS

N S 16 GOV

FEED VALVE

MR EQ PIPE

DUPLEX VALVE

PNEUMATIC CONTACTORS

CONTROL RESERVOER

N1 REDUCING VALVE COC

MR SAFTEY VALVE (10.5 Kg/cm2)

AIR INTAKE FILTER

BRAKE SYSTEM

Drain cock

Loading and unloading of compressor

To avoid the compressor running hot due to overloading and also to avoid the wastage of engine horse power, arrangements are provided to unload the compressor when a particular pressure is reached.

In these compressors unloading is effected by the unloaded plunger prongs pressing down the inlet valves of both L.P & H.P cylinders to keep them in open position as soon as 10kg/sq cm pressure is reached in the MR. It continues to be so till the pressure comes down to 8kg/sq cm.

The L.P cylinder air drawn in through the intake filter is thrown out in same direction. In H.P cylinder air is pushed back to the intercooler and L.P discharge manifold. This is achieved through the function of the unloaded plunger in conjunction with the air governor.

Expressor Lube oil pump An oil pump which is of chain driven and gear type circulates the oil

under pressure through the system. The oil pump is driven by a sprocket mounted on one of the two

pump gears which takes the drive from the crank shaft of the expressor through a sprocket and chain.

A strainer screen filters the oil before the oil is drawn up into the inlet port of the gear pump.

The filtered oil is carried under and around the gears to where the gears mesh.

The meshing action forces the oil upward to the discharge port. A port takes the oil up to the groove in distributing ring of the oil

pump body. from here oil flows to each crack-pin through drilled passages in the crankshaft.

Each crank-pin is cross drilled to supply oil to connecting rods. Oil pressure in the system is limited to 25-60 psi by a relief valve located in the oil pump body.

When the oil line pressure exceeds, the relief valve is unseated allowing oil to pass out to the sump.

Expressor Lube oil pump

•

Expressor crank case vacuum

The expressor crank case must have some vacuum to prevent oil throw over through the exhaust by preventing development of pressure in crank case.

Crank case vacuum is maintained by connecting the vacuum pipe to the crank case by a pipe connection through the crank case vacuum maintaining valve .

Normally in well maintained expressor a differential of 5” of vacuum is considered ideal which means when train pipe vacuum is 22” the crank case vacuum should be 17”.

Expressor Overhauling • Dis-assembly from loco-• All pipe lines are disconnected and removed.• Flexible coupling is uncoupled.• Foundation bolt is removed and expressor is lifted from loco. Overhauling Standard procedure• Dis-assembly of expressor on floor• Drain the crank case oil.• Remove the fast coupling from crank.• Remove the fan from coupling half.• Remove the intercooler, Exhaust manifold, safety valve.• Remove cylinder head, connecting rod, piston.• Remove the crank shaft key.• Remove the pump strainer after removing the set screw pin.• Remove the pump after uncoupling pump housing and pump

foundation bolt.

Expressor Overhauling • Remove both side oil seal.Remove pump drive chain after taking out

master link.• Remove cap screw of main bearing housing and housing to remove

by jacking.• Remove crank shaft with the help of hoist.• push the crank shaft downward to remove crank shaft with bearing.• Cut the pad for realignment. • Cleaning of components• All the components (piston, con rod, pump, valve, cap case side

cover, liner etc) cleaning in the K.Oil. Head and pipe cleaning in the caustic. After dip in caustic tank(16-18hrs) clean by water.

Wipe with khadi cloth.

Expressor Overhauling Inspection : visual inspection of components and rejected the defective material. Measure the L.P and exhaust piston Top- 7.732” max 7.726” min

Measure the H.P.Piston OD(4UC)-Top- 4.246” max 4.234” min. Measure the H.P.Piston OD(3UC) Top-- 5.492” max 5.483” min. Measure bore of cylinder liner at three location (top, bottom and

middle) L.P. cylinder- 7.750”min to 7.752”max H.P. cylinder (6CD4UC)- 4.250”min to 4.252”max H.P. cylinder (6CD3UC)- 5.500”min to 5.502”max Measure the piston ring gap and groove side clearance after refit

new ring with piston L.P (ring gap) .023” to .033” Side clearance 0.002” to 0.004” H.P (ring gap) .013” to .023” Side clearance 0.0015” to 0.003”

Inspection Contd.

Measure the crank pin dia -std -3.624” contd. Limit less then -3.6215” Measure the oil pump bearing collar to crank shaft -0.0045”

to 0.010” Measure the oil pump journal -4.5”(std). contd. Limit less then -4.498” Measure the lub oil pump bore-4.503”(std). contd. Limit less then -4.505” Lateral play of the crank shaft -0.005” to 0.050” Oil seal depth -0.792” to 0.832” Lift of inlet and discharge valve (0.072”- 0.082”)

Assembly Assemble the following in sequence: Fit pump, connecting rod, oil seal, liner, piston, both side

cover. Assemble the head with inlet discharge valve, unloader

valve, cap case. Blow by test at 0.5 kg/sq cm to 1 kg/sq cm pneumatic pressure of crank case for checking the leakage of oil seal, side cover, drain pipe, liner face joint. fit the head, intercooler, branch pipe, manifold pipe. Dye penetration of hub for checking of crack. Heating of hub at 200 F approx. L.U. Pipe, branches swivel breather pipe, fitting.

Assembly

Assembly expressor on test bench for 6hrs for following observation:

a) Crank case vacuum (6CD4UC) -22”min b) Crank case vacuum (6CD3UC) -21”min c) Lub oil pressure – 2kg/sqcm Performance of unloader valve –working

Measure gap between expressor crankshaft and engine crankshaft is 9/16” max.

Distance between the two hubs is 3.3/8”max and 3.1/8”min.

Distance from one end of each sleeve to the end of the hub should be between 2.1/2” to 2.3/4”.

Assembly

Angular misalignment:

Distance between the two hubs should be kept equal all round the circumference and tolerance of +0.006 is only permissible –measured by micrometer at every 90 degree.

Offset misalignment:

Measured by dial indicator while the crank shaft is manually rotated.

Backlash:

Some amount of clearance between the male and female couplings is provided.

Backlash of 0.024” at 3.5” radius when new. Max limit permitted after use is 0.001” at 3.5” radius.

FUEL INJECTION NOZZLE TEST

Expressor Trouble ShootingA.Expressor Running Hot- 1. Expr. Gov defective. 2. Excess crank case vac. 3. Continous loading of compr.& exhauster due to heavy

leakage in system or less efficient expr. 4. Expr.oil level low. 5. Oil throw from Expr.(burning of oil)B . Expr. Oil Throw-1. Low crank case vac2. Heavy blow bye from compr.cyl due to worn out piston

ring &liner3. Leakage from Expr. Oil seal.4. Leakage from liner insp cover gasket. 5. wrong setting of vac maintaining valve. 6. Expressor oil level high.

Expressor Trouble ShootingC. MR charging time more

1. Heavy leakage in system.

2. sticky valve/ leakage through valves.

3. unloader defective (bent pronge)

4. Inter cooler safety valve defective (blow earlier/leaking)

5. Inter cooler tube burst.

D.Vac creation less

1.Heavy leakage in system.

2.worn out rings & liner.

3.valve sticky /leakage through valve.

E. Oil pressure low

1.oil pump defective .

2.low oil level.

3.clearance between pump body & journal more.

4.strainer jam.

5. oil pressure relief valve defective.

6Chain loose

Thank you