Why air suspension is introduced?

 

Why air suspension is introduced?

Helical springs have limitation of damping and stiffness characteristics for high loads.

Air suspension on secondary suspension has been introduced by the Railways for

better riding and to eliminate the difference in buffer height on different loads

Air Spring Suspension in LHB Coach

ADVANTAGES OF AIR SUSPENSION

 Capable to sustain higher loads.

 Maintain constant floor height of coach.

 Provide better riding comfort.

 Reducing passenger fatigue

 Isolation of structure borne noise.

 Improved reliability, reduced maintenance effort.

Capacity of Air Springs in Different Type of coaches

LACCN-120 KN

LWACCW-120 KN

LWLRRM-140 KN

LS coaches-140

LSLRD-140 KN

LVPH coaches-140 KN

LWSCZDAC-140 KN

LWSCN-140 KN

In ICF coach AR above air spring is of 40 liters

Main components of Air Spring

The main components of Air suspension are Top plate, Air bellow, Emergency spring

and Sliding plate, fasteners and O rings

Cut section of Air Spring

It regulates the coach body level, irrespective of load condition of the vehicle, by charging or venting air spring bellows.

Working of Levelling Valve

The increase or decrease of height of vehicle due to decrease or increase of passenger

Levelling valve in turn actuates the handle of levelling valve to allow flow of some

compressed air through the circuit into the air spring or release of compressed air from

the air spring to atmosphere. Thus a fixed height of vehicle is always maintained

irrespective of change of passenger load. (294+0 -5

mm Height of spring) -2.5 degree

movement of lever is permitted from horizontal position

2. Operating Lever

3. Carrier with eccentric

4. Piston

5. Valve disc

V1  Check Valve

V2   Inlet Valve

V. Auxiliary Port

E. Exhaust port

L. Air Suspension Line

Duplex Check Valve

Duplex check valve is used in between the pipeline connection of the two air springs on

the two sides of a bogie. During the functional life of the pneumatic system, leakages at

the air spring cannot be ruled out. Duplex check valve is so designed that whenever a

pressure differential between the two air springs on each side of bogie due to leakage

and whatever reasons reaches a set pressure of 1.5 kg/cm2, the air will flow from one

air spring to other through the duplex check valve. Thus the uniform height between

the bogies / coach can be maintained till the leakages are attended.

Installation Lever

The installation lever is used to connect levelling valve to a bracket for proper levelling

of coach body.

The installation lever has ball and socket joint at both ends. When connected to levelling

valve lever, top and bottom ball socket joint of installation lever shall enable a free

simultaneous or independent movement

MAINTENANCE AND OVERHAUL: -

In the event of defect or damage or overhaul, the installation lever should be

dismantled and metal parts should be thoroughly cleaned using wire brush and

kerosene.

After all the parts are cleaned, they should be visually inspected especially: Ball and

socket joint and bearing surfaces for any scratch mark replace the parts if necessary

Maintenance of Air Spring in LHB Coaches

Inspection & maintenance of air spring

:

 Inspect for any water collection in rubber bellow of air spring

 Inspect the air spring for any damage or leakage

 Inspect air spring seat and top plates for corrosion, if corrosion noticed apply

primer & black paint duly ensuring proper surface preparation.

Inspection & maintenance of rectangular platform

provided on y- frame:

 Inspect air spring fixing holes of square platform provided on y- frame of bogie

for elongation, if elongated build them to dia. 22 mm.

 Inspect the corrosion on top surface of square platform provided on y- frame of

bogie. Remove the corrosion and paint with primer and black paint.

Inspection of pipe line:

 The air spring piping may be checked for any leakage/damage by soap test and

repair if required.

Leakage test of air spring:

Leak test of air spring assembly shall be carried out in test fixture as per following

procedure:

 Install the air spring assembly at working height (294+0-5).

 Gradually raise the air pressure to 9 kg/cm2 and disconnect the air supply.

 Air spring assembly shall be checked for pressure drop after 15 minutes at

internal pressure 9.0 kg/cm2. Drop of pressure at the completion of test shall be measured. The pressure drop

is required to be within 1% of the test pressure i.e. 9.0 kg/cm2.

Procedure for checking bogie clearances on ac and non ac

coaches with air springs:

 Place the coach at level track.

 Then maintain the bogie corner heights as per Bogie General Arrangement

drawing no. LG00004 Alt “a" of RCF for non AC Coaches

 After the bogie corner height is maintained, adjust the air spring height as

suspension diagram with the help of installation lever.

Procedure for adjustment of Installation lever.

 Keep the coach on a level track.

 Connect the pressure gauges to the drain plug locations of all 60 lit reservoirs in a

bogie.

 Adjust the length of all installation levers as per requirement to connect them to

lever of levelling valve

 Supply compressed air to the bogie.

 Adjust the design height of air spring to 294-0+5 mm by gradually increase or

decrease the length of installation lever.

 Repeat the same procedure for the other side of air springs of same bogie.

 Recheck the design height of all air springs of coach and make minor

adjustment if required to maintain the design height of all four air springs in

same coach between 294 to 289 mm.

CAUTION:

If the difference in pressure of the air in the air springs of the same bogie is more than

setting pressure of the duplex check valve i.e. Kg/cm2, then the air will continuously

escape from one air spring to the other through the duplex check valve and then to

atmosphere.

 Tighten the installation lever lock nuts with the horizontal lever of levelling

valve, so that the setting will not be disturbed.

 Repeat the above procedure for the second bogie.

 Disconnect the pressure gauges and replace the drain plug.

Checks for proper fitment of air spring assembly

 Check air spring vertical symmetry.

 No pre twist in air spring top plate during fitment.

 No push fittings in air spring holdings.

 Levelled top and base plate of air springProblem and their reasons

S.No

Nature of

problem

Reason

1

Inadequate bogie

clearances

 Improper initial settings of levelling valve.

 Improper functioning of levelling valve.

 Non uniform wear in bogie parts.

2

Failure of lateral

damper

 Damper fitting misalignment.

 Inadequate damper stroke.

 Pre angular twist in end fasteners due to level

difference.

3

Non lifting of air

spring

 Low air pressure.

 Heavy air leak in pipe connections.

 Fully choked levelling valve inlet port.

4

Delayed lifting of air

spring

 4 Perished rubber seat of lower diaphragm in

leveling valve.

 Partly choked wire mesh in leveling valve inlet

port.

 Back lash error in leveling valve rotation.Periodical inspection of air springs system on LHB Coaches

SCHEDULE

INSPECTION ON AIR SPRING SYSTEM

Schedule D1

 Visual check: General conditions which includes any external

damages, air leakage, infringement of any fittings, etc.

 Draining of 1 50-liters air reservoir of air spring.

 Checking of spring height with gauge & adjustment height by

operation of installation lever.

 Check the position of isolating cock and drain cock, these should

be on and off position respectively.

Schedule D2

As in Schedule D1 &

 Checking of installation lever with inflated air spring for normal

function, tightening of installation lever nuts and protection

screen nuts, tightening of bracket of all flexible hoses.

 Cleaning of air filter of 1 50-liters reservoir.

 Draining of 60-liters reservoir.

 Cleaning of leveling valve filter as per manufacturer’s manual.

Schedule D3

As in Schedule D2 &

 Thorough checking of air spring, bulging of bellow, air leakage.

 Air suspension pipe leakage check by using soap water.

 Removing dust mud & oil deposit if any, on air spring and

control equipment.

 Thorough checking of square platform provided on y- frame of

bogie for any crack and deformation.

 Tightening of air spring bottom plate bolts and nuts.

 Measurement of bogie clearances related to air spring.

SS l/SSII

As in Schedule D3 &

 Through visual check of air spring after dismantling.

 Remove all valves and carry out external cleaning, overhauling

and function test should be done as given in maintenance

manual supplied by respective vendors.

 Checking securing arrangement of steel pipeline.

 Leakage test of air springs.

 Installation lever adjustment.

 Lateral damper condition should be checked and replace with

fresh if damaged.

 Air spring bellow should not be painted.

 Inspect the corrosion on top surface of square platform provided

on y- frame of bogie, Remove the corrosion and paint with

primer and black paint.