Automatic, but not maintenance free

Since the purpose of automatic slack adjusters (ASA) is to maintain proper shoe-to-drum clearance in all braking modes, how reliably it performs this task can affect braking performance and brake life.

Meritor emphasizes that even though they’re automatic, ASAs are not maintenance-free. Fleets must periodically check for grease, with intervals determined by vocation. Slack adjusters used in linehaul operations, for example, don’t have to be checked as often as those used in frequent-braking service such as garbage trucks and school buses. Crewson Brunner recommends greasing when you do PM on the brake system.

Most manufacturers also recommend greasing slack adjusters at installation whether they’re supplied loose or preassembled to the brake. Meritor points out that even though pre-assembled slack adjusters have been greased at the manufacturer, it’s prudent to grease them when you take delivery of a vehicle. Exceptions are no- or low-maintenance ASAs, such as those standard on Meritor’s LX500 Q Plus cam brakes.

Automatic, but not maintenance freSince the purpose of automatic slack adjusters (ASA) is to maintain proper shoe-to-drum clearance in all braking modes, how reliably it performs this task can affect braking performance and brake life. Meritor emphasizes that even though they’re automatic, ASAs are not maintenance-free. Fleets must periodically check for grease, with intervals determined by vocation. Slack adjusters used in linehaul operations, for example, don’t have to be checked as often as those used in frequent-braking service such as garbage trucks and school buses. Crewson Brunner recommends greasing when you do PM on the brake system.Most manufacturers also recommend greasing slack adjusters at installation whether they’re supplied loose or preassembled to the brake. Meritor points out that even though pre-assembled slack adjusters have been greased at the manufacturer, it’s prudent to grease them when you take delivery of a vehicle. Exceptions are no- or low-maintenance ASAs, such as those standard on Meritor’s LX500 Q Plus cam brakes.

Bendix recommends greasing slack adjusters at, every 25,000 miles or at PM, as well as at installation. The company’s ASA-5 SureStroke, an unhanded unit for tractors and trailers, is designed with a fitting for the mechanic’s grease gun. You know the ASA is properly lubed when clean grease flows out of the boot.

Dana Spicer, which sells ASAs made by Haldex, offers units with three levels of lubrication. The traditional ASA requires lubrication annually. A second model has a special fitting that comes with low-lube LMS brakes; lube intervals are 250,000 mi. A no-lube version is available with Spicer No-Lube LMS brakes.

After brakes have been relined, Meritor recommends adjusting the ASA manually to a certain clearance and then letting the slack adjust to proper clearance. Since the slack adjuster’s function depends on having brakes fully back, it’s also important to replace the shoe-return spring with a new one when a brake is relined.

Crewson Brunner cautions that making too many manual adjustments can cause ASAs to wear out prematurely. If the ASA isn’t holding adjustment, then you have either a faulty unit, an incorrect installation or a problem with the foundation system. And according to Bendix, other indications that an ASA is not working properly include one side of the vehicle braking more aggressively or an angle that’s greater than 90 deg. between the slack adjuster and the chamber pushrod.

Manufacturers agree that different brands of ASAs should not be used on the same axle. Since slack adjusters are designed to maintain clearance slightly differently or set up at various angles, depending on the brand, mixing brands could create an imbalance. When it comes to using different brands on different axles, opinions vary slightly. Some say it’s not an issue at all; others say it’s better to use the same brand, but admit that the consequences of not doing so are nowhere near as severe as they are for mixing brands on the same axle.

Haldex, which uses the term automatic brake adjuster, or ABA, introduced a self-setting option earlier this year. The S-ABA is designed to function correctly no matter what the position of the control arm. By eliminating the control-arm adjustment needed to get correct running clearance, installation of the S-ABA brake adjuster is faster and easier.

Crewson Brunner offers Auto Grease and Auto Check options on its slack adjusters. Auto Grease lets you keep the S-cam fully lubricated when you grease the ASA. “The specially designed spline gear has a groove in the center that allows grease to flow to the S-cam, promoting longer life for the S-cam and ASA,” says the company. Auto Grease will become standard on Crewson Brunner slack adjusters later this fall. Auto Check gives you a visual indication of ASA status. When brakes are applied, a pointer measures working stroke and confirms that the ASA is functioning properly.

Gunite ASAs sport several design changes this year, including a precision fit, collar-lock clevis that provides tight tolerance between the push rod and clevis that reduces maintenance time by enabling technicians to dis-assemble the slack from the brake without having to take the pins out. A self-lubricating worm wheel also decreases maintenance requirements.

What does the future hold for ASAs? Although we’re not likely to see much change in basic design, “smart” vehicle technology could one day expand the role of this component. Dana Spicer envisions the day when smart ASAs will provide electronic feedback to warn drivers of problems

INSPECTION RECORD

JOB NO………………..

DATE………………….

1) Chassis No……………                          2) Engine No………………………………..

3) Vehicle Reg. No…………….                 4) Kms………………………………………

5) Nature of failure………………………………………………………………………..

6) Kms covered after last rebuild…………………………………………………………

01. CYLINDER BLOCK

Block No…………………

02. CRANK SHAFT

Crank shaft no……………………….

03. CONNECTING ROD

04. CYLINDER HEAD

05. ROCKER LEVER/PEDASTALS/TAPPETS PUSH ROD

06. CAMSHAFT

07. VIBRATION DAMPER

08. PISTON PIN

09. OIL FILTER HEAD

10. OIL COOLER

11. OIL PUMP

12. WATER PUMP

13. FAN HUB

14. BELT TENSIONER

15. THERMOSTAT

16. TURBO CHARGER

17. EXHAUST MANIFOLD

wORKING PRINCIPLE OF air COMPRESSOR

During normal operation this valve permits a particular value of hold-off pressure to the spring brakes thereby keeping it released. This hold-off pressure can be varied from 4 bar to 7 bar.

During parking of the vehicle, this valve quickly exhausts air from the spring brakes thereby allowing a fast application of the spring brakes

Prevents compounding of service brake and spring brake

Modulates application of spring brakes in the event of a failure in the primary service circuit

Current layout and function

The piping diagram indicating the positioning of the inversion valve along with the double check valve and the relay valve is indicated in figure 1.

Figure 1 – Current layout

a) Providing hold-off pressure to release the spring brakes: With the park control valve in the ‘on’ condition, air pressure from the reservoir flows through the park control valve and through the double check valve to the control port of the inversion valve. The inversion valve upon receipt of this signal air pressure communicates supply air to delivery. This delivery air pressure is then used as the signal air pressure to the relay valve. The relay valve on receipt of this signal delivers hold off air pressure to the spring brakes thereby releasing the brakes.

b) Applying spring brakes: With the park control valve shifted to the ‘off’ condition, signal air pressures to the inversion valve and consequently to the relay valve are depleted. This causes air in the spring brakes to quickly exhaust through the relay valve thereby applying the spring brakes.

c) Preventing compounding of service brake and spring brake: With the spring brakes in applied condition, operation of service brakes will result in air from the primary delivery of the dual brake valve to flow through the double check valve and then on to the control port of the inversion valve. Spring brakes are then released as detailed in (a) thereby preventing the compounding of the service brake and the spring brake.

d) Modulation of the spring brakes: In the event of failure in the primary circuit, air from the secondary service is used to modulate the spring brakes with the help of the relay valve.

Inversion valve with anti-compounding and relay

In the inversion valve, all the four functions are achieved with one valve. The functions served by the double check valve and the relay valve are integrated with the inversion valve.

The major components of the inversion valve are the valve body, top cover, primary piston, relay piston, an integrated double check valve, inlet/exhaust valve and graduating spring (refer figure 2).

This valve has five modes of operation and they are detailed below:

1. Spring brakes released

When the system is being charged, air pressure enters the supply port and is present in the cavity beneath the inlet/exhaust valve. The inlet/exhaust valve is in contact with the inlet valve seat in the body thus preventing passage of air to delivery as well as through the exhaust. When the full system pressure is reached, the ‘park control valve’ can be operated to release the spring brakes. The park control valve is a manually operated on/off valve. Shifting the park control valve to the ‘on’ condition ensures continuous supply of air pressure at the spring brake control port of the inversion valve. Pressurised air at the spring brake control port then enters the double check valve, deflects the diaphragm, and flows into the cavity on top of the primary piston through the cross-hole provided in the top cover. This air pressure forces the primary piston to move downward and contact the relay piston. The relay piston then moves downward and contacts the inlet/exhaust valve. Further movement of the relay piston opens the inlet passage thereby allowing air to flow from the supply port to the delivery ports. Consequently the spring brakes are released. At the same time the exhaust valve seat in the relay piston prevents loss of air through exhaust. The valve in this mode of operation is illustrated in figure 4.

_

Figure 4 – spring brakes released

The limiting value of the hold-off pressure (or pressure at the delivery ports) to the spring brakes can be varied between 4 bar and 7 bar by changing the spring load on the relay piston with the help of the adjustment screw. The air pressure that is communicated to the delivery ports also acts on the underside of the relay piston. When the airhead load on the relay piston equals the load exerted by the graduating spring, the valve is in the ‘balanced’ condition. In this condition the inlet valve seat and the exhaust valve seat are in the same plane thereby preventing further flow of air to delivery ports and at the same time preventing loss of air through exhaust. This condition is illustrated in figure 5.

Figure 5 – Balanced condition

2. Spring brakes applied

The park control valve is switched to the ‘off’ position to apply the parking brakes. Consequently, air pressure at the spring brake control port and on top of the primary piston is exhausted through the park control valve. The primary piston then moves upward. Airhead load beneath the relay piston forces it to move upward thereby opening the exhaust passage and sealing the inlet. Air from the delivery ports is then exhausted thereby applying the spring brakes. This condition is illustrated in figure 6.

Figure 6 – Spring brakes applied

3. Simultaneous application of service brakes and spring brakes applied (Anti-compounding)

Application of service brakes provides air pressure at the primary service port P1 and secondary service port P2. There is no air pressure in the spring brake control port since the spring brakes are applied. Air entering the service port P1 deflects the diaphragm in the double check valve and seals the passage in the spring brake control port. Air then flows through the cross hole provided in the top cover to the top of the primary piston. This air pressure forces the primary piston to move downward and contact the relay piston. The relay piston then moves downward and contacts the inlet/exhaust valve. Further movement of the relay piston opens the inlet passage thereby allowing air to flow from the supply port to the delivery ports. Consequently the spring brakes are released thereby preventing the compounding of the service brake and the parking brake. This condition is illustrated in figure 6. Continuous application of the service brakes results in the ‘balanced’ condition explained earlier.

Figure 6 – Service brakes applied with spring brakes released

Air that enters the valve body through the ports P1 and P2 gets neutralised since the pressure and sealing areas on the top and bottom of the relay piston are essentially equal.

4. Application of spring brakes with primary in failed condition (Modulated application)

In the event of failure in the primary circuit, air pressure, upon application of service brakes will be available only in the secondary service port P2. However, air pressure will be available at the spring brake control port and consequently the delivery ports thereby keeping the spring brakes released. Air that enters the valve through the secondary service port P2 acts beneath the relay piston and forces the piston to move upward thereby exhausting air from the delivery ports and applying the spring brakes. The air released from the spring brakes will be proportional to the pressure at secondary service port P2 thus providing the driver with a modulated application of the spring brakes. This condition is illustrated in figure 7.

Figure 7 – Application of service brakes with primary in failed condition

Unique features of the valve

1. Integrated relay and inversion functions

In a typical air brake circuit that complies with FMVSS 121 regulations, all the above-mentioned functions are achieved by a combination of three different valves, namely, a double check valve, an inversion valve and a relay valve. However, in the inversion valve the functions accomplished by the combination of the above three valves have been integrated into one single valve. Therefore, the inversion valve can be directly replaced with the combination of the three valves.

2. Inversion, pressure-limiting and relay functions are achieved by the same valve

The same combination of relay piston and inlet/exhaust valve in the inversion valve is used to achieve all the three functions, namely, inversion, pressure limiting and relay. Normally the pressure limiting and inversion functions are achieved by the combination of piston and inlet/exhaust valve in the inversion valve, and the relay function is achieved by another similar piston/valve combination in the relay valve.

3. Pressure limiting is achieved by caging the spring

Limitation of hold-off pressure to the spring brakes is achieved by caging the graduating spring between the spring guide and the spring retainer. Normally in such applications one end of the graduating spring is always made to rest on a stationary surface. In ’s valve the unique feature is that the entire spring assembly is in a caged condition and allowed to move along with the relay piston even as it provides the necessary load to achieve the pressure-limiting function.

4. Split arrangement of relay piston

The split arrangement of relay piston makes the valve more stable and insensitive to pressure lead from primary service port. Also the split arrangement of relay piston makes the valve resistant to false actuation of the valve during a traction control situation.

Working Principle and construction

The condenser oil separator is used in air brake system fitted with Air dryers. Air dryer is used to remove moisture from the compressed air. The moisture removal performance of air dryer is dependant on desiccant. When the desiccant in air dryer is affected by oil contaminants present in compressed air, the drying efficiency of air dryer reduces. By fitting condenser oil separator before air dryer, the oil contaminant are removed prior to air dryer and thereby increases air dryer life.

2. Function:

The main functions of condenser oil separator are:

· Removes moisture condensate and oil from the compressed air

· Ejection of collected condensate and oil during cutout cycle.

3. Construction and Operation:

The cut section of condenser oil separator is shown in fig. 2. Condenser oil separator consists of a head, body and baffle. Seal housing fitted with filter houses seal, which is retained against drain valve body by conical spring and spring seat. The seal seals air pressure and condensate collected during charging and automatically exhausts the condensate during cut out. The head has inlet and delivery port for air line connection.

Condenser oil separator operates in two cycles. They are

· Cut in cycle – Compressor charging the system

· Cut out cycle – Compressor unloading

3.1 Cut in cycle:

The compressed air delivered from compressor enters through the inlet port. The air is then circulated through the head and then passes into body. Compressed air is cooled when it is circulated through head and body. Then the air is passed into baffle where it is subjected to centrifugal action. Due to centrifugal action, the oil particles present in the air will flow through the inner walls of body and then passes through filter. Condensed moisture also flows through inner walls and then passes through filter. The filter filters solid carbon particles.

Filtered condensate will flow through lip seal via. Seal housing and collects in the drain valve body. The condensate is sealed by conical portion of seal due to spring force. Clean air will then pass through inner portion of baffle, and then passes through the delivery port.

3.2 Cut-out cycle:

During cut out cycle, the compressed air acting above the seal is discharged to atmosphere through the unloader valve. The pressure acting above the seal will the less than the pressure acting below the seal. This pressure differential causes the pressure acting below the seal to lift against spring force and the seal lip seals the air pressure in the seal housing. As the seal is lifted above the conical seat of drain valve body, the entrapped pressure purges out the condensate collected into the atmosphere.

The cycle is repeated during the entire period of operation

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FUNCTION

This valve controls twin line brake system on a trailer from the towing vehicle fitted with Dual Brake System and the Hand brake valve for Spring brake actuators.

In addition, this valve also helps to apply the brakes automatically in the trailer when service brakes are applied on the tractor by exhausting the supply line (12) in the event of failure in the service line (22).

DESCRIPTION

Trailer control valve mainly consists of a Direction control valve and a trailer control valve.

Direction control valve has a valve body housing a piston assembly in the top bore with a spring and cover and secured in position by a circlip. This valve has an inlet, a passage for connecting the inlet to the trailer control valve and two more passages in which one to chamber connecting to service line (22) and the other to chamber connecting to Primary delivery line (41). This valve is secured onto the middle body of the trailer control valve.

Trailer control valve has a Upper body, a middle body and a Lower body.

Between the upper and the middle body a relay piston assembly with a return spring is located. The relay piston assembly has another piston with a spring, a spring guide and an adjusting screw in the bore and secured by a circlip.

In the middle body top bore and below relay piston assembly an emergency plunger assembly is located. The emergency plunger assembly has a spring loaded valve and a piston located in the bottom side and secured in position by a circlip. A diaphragm with upper and lower follower is located on the other side of the piston and secured by a flat hexagon nut. The outer lip of the diaphragm is located between the middle and the lower body. The free end of the piston is guided in the bore of the lower body and an exhaust check arrangement is secured to the lower body.

The upper body has a port (41) connecting to primary delivery line from Dual brake valve and a passage connecting to Direction control valve.

The middle body has a passage connecting to the inlet (1) from Direction control valve, supply port (12) and Service port (22) connecting to trailer, port (43) connecting to the delivery line of Graduated hand control valve and a passage connecting to Direction control valve.

The lower body has a port (42) connecting to the secondary delivery line from Dual brake valve.

CHARGING ( AIR SUPPLY TO TRAILER & BRAKES OFF POSITION)

· When the braking system is charged, the air supply enters through port 11 of the Direction control valve and acts at bottom of the piston pushing it to the upper stop against the spring force.

· The air supply goes to the supply line through the chamber connecting to port 12.

· If the tractor is coupled to the trailer, the trailer Reservoir is getting charged through the Relay emergency valve fitted on the trailer.

· In this process, air pressure acting below the emergency plunger moves it along with the valve upwards and the valve comes into contact with the piston closing the exhaust passage and subsequently opening the inlet passage, allowing the air supply to service line through the chamber connecting to port 22. This leads to brake application in the trailer.

The brakes are applied both in tractor and trailer as long as the Graduated hand control valve is in “BRAKES ON” position

· When the hand brake is released ( i.e. Graduated hand control valve in “BRAKES OFF” position ) air is supplied to chamber through port 43.

· Air pressure in the chamber acting on the upper side of the diaphragm pushes the piston downwards along with the emergency plunger. This leads to closing of inlet passage and subsequent opening of exhaust passage allowing the exhaust of air from the service line connecting port 22 ; thereby releasing the brakes in the trailer.

· At the same time, the spring brakes in the tractor are also getting released by air supply through Graduated hand control valve.

Brakes partially applied ( Predominance )

In brakes partially applied condition, air pressure in the chamber connecting to port 22 depends on the pressure acting on the relay piston (36) and the preload of the spring (35).

The preload of the spring (35) can be adjusted by the screw (32).

The preload of the spring is set to ensure that the outlet pressure in port 22 is higher by 0.5 ± 0.2 bar as compared to pressure at port 41.

The operation sequence from 1 to 4 continues and the air pressure acting below the relay piston (36) and piston (30) in chamber connecting to port 22 when exceeds 0.5 ± 0.2 bar as compared to the pressure in chamber connecting to port 41, the piston (30) alone moves upwards overcoming the preload of spring (35) and closes the inlet preventing further charging of chamber connecting to port 22.

This is the predominance position.

Secondary

At the same time as air enters port 41, air from secondary delivery of Dual brake valve also enters chamber connecting to port 42 and acts below diaphragm (44).

However, the pressure in chambers connecting to port 22 and port 43 acting above the emergency piston (26)and diaphragm (44) respectively is greater and the position of the piston is unaltered.

If brakes are partially applied, the pressure that builds in chamber connecting to port 22 again forces emergency piston (26) downwards. Thus the inlet passage closes and a balanced condition is reached.

Secondary failed

· When the brake is applied on the tractor, air is supplied to port 41 and its chamber.

· Air pressure in chamber acts on relay piston (36) and piston (30) pushes the pistons together downwards, thereby the piston (30) comes into contact with the valve (25) closing the exhaust passage and subsequently opening the inlet passage, allowing air supply into chamber connecting to port 22. (i.e. into the service line of the trailer )

· This leads to brake application in the trailer.

If the secondary of the Dual brake valve fails, operation of the valve is controlled by air from primary. In this case, the operation of the valve is with predominance

Primary Failed

· When brake is applied on the tractor, air is supplied to port 42 and its chamber.

· Air pressure in the chamber acts below the diaphragm (44) and pushes the emergency piston assembly upwards; thereby the valve (25) comes into contact with piston (30) closing the exhaust passage and subsequently opening the inlet passage allowing air supply into chamber connecting to port 22.(i.e. into the service line of the trailer )

· This leads to brake application in the trailer.

If the primary of the Dual brake valve fails, operation of the valve is controlled by air from secondary. In this case, the operation of the valve is without predominance.

Hand brake application

· When the Graduated hand control valve is in “BRAKES ON” position, air from the chamber connecting to port 43 and also hand brake line of Spring brake actuators is depleted through Graduated hand control valve.

· Automatically the relay piston assembly is pushed up by the air pressure in chamber connecting to port 12 and inturn the valve (25) gets into contact with piston (30) closing the exhaust passage and subsequently opening the inlet passage, allowing the flow of air into chamber connecting to port 22. ( i.e. air is supplied to service line of the trailer )

· This leads to automatic emergency brake application in the trailer.

Service line of trailer failed

· In a running vehicle if the service line of trailer breaks from port 22, no air pressure builds up in chamber connecting to port 22 when the service brake on the tractor is applied.

· The piston (10) is then pushed downwards by the air pressure in chamber connecting to port 41 and the flow of air supply from port 11 to port 12 is metered (reduced) by reducing the flow passage from 8 mm dia to 2 mm dia.

This is the Dumping operation.

· At the same time, air pressure in the chamber connecting to port 41 pushes the relay piston (36) and piston (30) together downwards and simultaneously pressure in chamber connecting to port 42 acting on the bottom of the diaphragm (44) pushes the emergency piston assembly upwards.

· Thus the valve (25) comes into contact with piston (30) closing the exhaust passage and subsequently opening the inlet passage.

· This helps to deplete air from chamber connecting to port 12 and the supply line of trailer through the point at which the service line failed, resulting in automatic emergency brake application in the trailer.

The pressure in the supply line of the trailer ( port12 ) comes down to 1.5 bar in less than 2 seconds.