4. MODEL IMPLEMENTATION
4.1. Geometry definition
SPRING PARKING
BRAKES
BRAKES
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Mountinounting Boltsg Bolts
Spring parking
Spring Parking Brake Systems Spring Parking Brake Systems (Single circuit system only) (Single circuit system only)
The installation of spring parking brakes and their The installation of spring parking brakes and their piping arrangements into a vehicle air brake system piping arrangements into a vehicle air brake system will vary depending on the vehicle make.
will vary depending on the vehicle make.
Spring parking brakes may be installed on an air Spring parking brakes may be installed on an air brake- equipped vehicle for use as a reliable parking brake- equipped vehicle for use as a reliable parking brake system. In the service br
brake system. In the service brake system, ake system, the brakesthe brakes are applied by air pressure and retracted by springs.
are applied by air pressure and retracted by springs.
In the spring parking br
In the spring parking brake system, ake system, the brakes arethe brakes are applied by spring pressure and retracted by air applied by spring pressure and retracted by air pressure. The s
pressure. The spring parking brpring parking brake chambers areake chambers are attached to the service brake chambers and operate attached to the service brake chambers and operate through the same linkage, therefore the effectiveness through the same linkage, therefore the effectiveness of the spring parking br
of the spring parking brake depends ake depends on the serviceon the service brake adjustment. A control val
brake adjustment. A control valve (operated by ave (operated by a squa
square, yellow button) located in the cre, yellow button) located in the cab allows theab allows the driver to exhaust air out of the spring parking brake driver to exhaust air out of the spring parking brake circ
circuit to apply the brakes, uit to apply the brakes, or pressurizor pressurize the cire the circuit tocuit to release t
release them. Shem. Some systems may have an additionalome systems may have an additional valve contr
valve controlled by a blue button that applies only theolled by a blue button that applies only the tractor
tractor spring parking brakespring parking brakes and not the trailer s and not the trailer springspring parking brakes. The sys
parking brakes. The system can also actem can also act as an emer-t as an emer-gency brake. Loss o
gency brake. Loss of air f air from the system may auto-from the system may auto-matical
matically apply the brakes, deply apply the brakes, depending on how theending on how the system is piped.
system is piped.
C
Control valves wontrol valves will varill vary, y, depending on thedepending on the manufacturer and type of piping arrangements.
manufacturer and type of piping arrangements.
A spring-loaded valve requires that the valve be A spring-loaded valve requires that the valve be pushed in to release the spr
pushed in to release the spring parking brakes. Thising parking brakes. This valve cannot be left in the r
valve cannot be left in the released position beloweleased position below approximately 35 psi in the system. Any time the approximately 35 psi in the system. Any time the reservoir
reservoir pressure drops to approximately 35 pressure drops to approximately 35 psi,psi, this valve will exhaust automatically, placing the this valve will exhaust automatically, placing the spring parking br
spring parking brakes into full applicakes into full application. Oation. On somen some older vehic
older vehicles there may be a single type of push-les there may be a single type of push-pull cont
pull control valve that does not have an automaticrol valve that does not have an automatic release featur
release feature. Te. To apply the spring parkio apply the spring parking brakes,ng brakes, the valve must be oper
the valve must be operated manually, eveated manually, even thoughn though the reservoir pressure has been depleted.
the reservoir pressure has been depleted.
During normal operation, air pressure cages During normal operation, air pressure cages
(compresses) the spring, holding it ready for parking (compresses) the spring, holding it ready for parking or emergency braking.
or emergency braking.
12 12 12 12 27
27
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Mountounting Boltsing Bolts Clevis and pin Clevis and pin Slack
Slack adjuster adjuster
Push rod Push rod
Diaphragm Diaphragm return return spring spring
Diaphragm Diaphragm
Spring parking Spring parking brake chamber brake chamber Dust Dust cap cap Parking brake Parking brake
spring spring Service brake
Service brake chamber chamber
Service Brakes Applied Service Brakes Applied Brake On
Brake On O
On the pre-n the pre-tritrip air brp air brake inspection (Sectiake inspection (Section 9on 9), you), you must ensure that the parking brake spring is not must ensure that the parking brake spring is not manually caged or it w
manually caged or it will not expand and apply theill not expand and apply the brake. The b
brake. The brake crake chambers should be checked fhambers should be checked foror cr
cracks and damage. Tacks and damage. The brake chamber should behe brake chamber should be fitted wit
fitted with a dust cap to ensh a dust cap to ensure debris will not enterure debris will not enter the chamber.
the chamber.
During normal service brake operation, the parking During normal service brake operation, the parking brake spring does not expand. Air pr
brake spring does not expand. Air pressure keepsessure keeps the spring caged.
the spring caged.
Using a Spring Parking Brake Using a Spring Parking Brake
Spring parking
Spring parking brakes (12brakes (12), added to the br), added to the brakeake chambers of the rear axle on the single unit vehicle, chambers of the rear axle on the single unit vehicle, are ill
are illustrated. A custrated. A control valve (27ontrol valve (27) is mounted in) is mounted in the cab.
the cab.
A supply line of reservoir air is piped from the dry A supply line of reservoir air is piped from the dry reservoir to the control valve. Opening the control reservoir to the control valve. Opening the control valve a
valve allows reservoir air pressure to flow llows reservoir air pressure to flow to theto the spring parking brake c
spring parking brake chambers, releasing them.hambers, releasing them.
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Mountinounting Boltsg Bolts Clevis and pin
Closing the closing the control valve shuts off ontrol valve shuts off the supplythe supply of reservoir air pressure and exhausts the of reservoir air pressure and exhausts the existing pressure in the spring parking brake existing pressure in the spring parking brake chambers. This mo
chambers. This motion allowtion allows the spring tos the spring to expand, applying the brakes.
expand, applying the brakes.
Caution:
Caution:Parking brakes should be in the releaseParking brakes should be in the release position before making a service brake application.
position before making a service brake application.
A full-brake application, made when the parking A full-brake application, made when the parking brakes are applied, can compound the force exerted brakes are applied, can compound the force exerted on the slack adjusters and linkage and result in on the slack adjusters and linkage and result in damage or brake f
damage or brake failure. Comailure. Compounding is thepounding is the combination o
combination of twf two forces: the force applied by theo forces: the force applied by the spring brakes and the service brake.
spring brakes and the service brake.
Spring brakes are primari
Spring brakes are primarily used as a ly used as a parking brake,parking brake, but in the event of loss of air pressure in the system, but in the event of loss of air pressure in the system, they can assist in stopping the vehicle. How quickly they can assist in stopping the vehicle. How quickly they will
they will stop the vehicle depenstop the vehicle depends on such factorsds on such factors as:
as:
·
·
the weight and speed of the vehicle;the weight and speed of the vehicle;·
·
the steepness of the grade;the steepness of the grade;·
·
the spring force of the spring brakes that havethe spring force of the spring brakes that have been installed; and,been installed; and,
·
·
the adjustment of the service brakes.the adjustment of the service brakes.If the brakes have overheated, such as during If the brakes have overheated, such as during
mountain driving or hard highway braking, care must mountain driving or hard highway braking, care must be taken when parking the vehicle. If the spring be taken when parking the vehicle. If the spring parking brakes are applied w
parking brakes are applied when the brake drum hashen the brake drum has expanded because of extreme heating, when the expanded because of extreme heating, when the brake drum starts to c
brake drum starts to cool and contract, the pressureool and contract, the pressure exerted by the spring parking brake may cause the exerted by the spring parking brake may cause the brake drum to crack
brake drum to crack or wor warp. When parking a vearp. When parking a vehiclehicle w
with over heated brakes, park on level ground, stopith over heated brakes, park on level ground, stop the engine and leave the transmission in the lowest the engine and leave the transmission in the lowest gear and block the w
gear and block the wheels. Dheels. Do not set the springo not set the spring parking brakes until you have verified the br
parking brakes until you have verified the brake drumake drum is cool to the touch.
is cool to the touch.
Spring Parking Brakes Applied Spring Parking Brakes Applied Brakes On
Brakes On
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Mountinounting Boltsg Bolts
Spring parking
Parking Brake Spring Caged Parking Brake Spring Caged Brakes Off
Brakes Off Mechanical Release (Caging)
Mechanical Release (Caging) Some spring parking brakes can be r
Some spring parking brakes can be releasedeleased mechanically by “winding them off” or “caging”
mechanically by “winding them off” or “caging”
them. C
them. Caging means the brakes araging means the brakes are being released.e being released.
This is achieved with a bolt that runs through the This is achieved with a bolt that runs through the centre of the c
centre of the chambhamber bodyer body, which , which is turned tois turned to compress the spring. It may be necessary to fir compress the spring. It may be necessary to firstst remove a lock plate and stud to gain acc
remove a lock plate and stud to gain access to theess to the head of the bolt. O
head of the bolt. Other types have a dust cther types have a dust cap thatap that must first
must first be removed and a bolt inserted. In somebe removed and a bolt inserted. In some cases, a spe
cases, a special wcial wrench is rrench is required. equired. Instruction onInstruction on how to “
how to “cage” cage” is usually is usually on the bodon the body of the parkingy of the parking brake chamber. If all air is lost and the vehicl
brake chamber. If all air is lost and the vehicle has toe has to be tow
be towed, the parking brakes can be released byed, the parking brakes can be released by caging them.
caging them. Always block the wAlways block the wheels when cagingheels when caging the parking brake spring.
the parking brake spring.
Warning Warning
Spring parking brake chambers should never be Spring parking brake chambers should never be disassembled without first compressing the spring disassembled without first compressing the spring w
with a caging bolt. These springs are under extremeith a caging bolt. These springs are under extreme pressure and could cause serious personal injury if pressure and could cause serious personal injury if disassembly is attempted by anyone not
disassembly is attempted by anyone not experienced in ser
experienced in servicing these units. Disassembly ovicing these units. Disassembly off a spring brake chamber should only be prefor
a spring brake chamber should only be preformedmed by a qualified mechanic or tec
by a qualified mechanic or technician.hnician.
Secti
Section Summary Qon Summary Questionsuestions 1 parking brake control valve?
parking brake control valve?
5 brakes before making a full brake application brakes before making a full brake application test? released without the use of air
released without the use of air pressure?pressure?
9
9.. What is What is the the dandanger oger of disf disassassememblinbling a g a sprinspringg parking brake unit?
parking brake unit?