air is permitted to pass through the bleed passage
piston on the lower portion. When either the upper
and enters the cavity above the outer relay piston.
or lower piston is moved down all the way, the inlet
The pressure moves the outer relay piston and the
v a l v e s remain open and full reservoir pressure is
inner relay piston down. As the inner and outer re-
delivered to the actuators.
lay pistons move down, the seat on the inner relay
seals off the exahust valve, and at the same time
RELEASING
moves the lower inlet valve off its seat, permitting
air pressure to flow out the lower delivery port to the
UPPER PORTION
brake actuators applying the brakes. Because of the
small volume of air required to move the outer relay
If the treadle or pedal application is released, and
piston, action in the lower portion of the valve is
mechanical force is removed from the top of the
almost simultaneous.
piston air pressure and spring load will lift the
piston opening the exhaust in the valve. The air
OPERATION-LOSS OF AIR IN LOWER CIRCUIT
below the piston and in the delivery line is then
exhausted through the exhaust port.
Should air be lost in the lower circuit, the top por-
tion will continue to function as described above,
LOWER PORTION
under "Upper Portion."
If the treadle or pedal application is released, air
LOSS OF AIR IN UPPER CIRCUIT
above the relay pistons is exhausted and the air
p r e s s u r e and spring load beneath the pistons will
Should air be lost in the upper circuit the function
will be as follows: As the treadle or pedal is de-
below the piston and in the delivery lines is then
pressed, and no air pressure is present in the upper
exhausted through the exhaust port.
supply and delivery ports, extended treadle travel
and continued mechanical force will move the inner
relay piston down, sealing the exhaust seat and
PREVENTIVE MAINTENANCE
moving the inlet valve off its seat allowing air pres-
sure to flow out the delivery port to the brake cham-
Every 200 Operating Hours or Monthly:
bers applying the brakes.
Lubricate treadle or lever roller and roller pin.
Also, hinge pin on treadle type valve and linkage to
BALANCED
lever type valve. Use engine oil for this lubrication.
UPPER PORTION
Lift boot away from plunger or mounting plate
When the air pressure in the cavity beneath the
and put a few drops of light engine oil between
piston and the air pressure being delivered to the
plunger and mounting plate. Avoid using too much
brake actuators equals the mechanical force on top
oil because it could get on the rubber spring and
the piston, the piston lifts and the inlet valve closes,
can cause it to deteriorate.
stopping the further flow of air from the supply line
through the valve. The exhaust remains closed pre-
Clean exhaust check depending on type of ser-
venting any escape of air through the exhaust port.
vice.
LOWER PORTION
T h e linkage of the lever operated type valve
should be checked for operation and adjusted if it
When the air pressure beneath the outer relay
is not operating properly. Check that it is free from
p i s t o n approaches that being delivered above the
obstructions and does not bind or bend throughout
piston, the piston spring lifts the piston slightly and
its full travel. Worn or damaged parts should be
the inlet valve spring returns the inlet valve to its
replaced.
s e a t . The exhaust remains closed as the supply
pressure balances the delivery pressure.
Every 3,600 Operating Hours or Yearly:
When applications in the graduating range are
It is recommended that the inlet and exhaust
made, a balanced position is reached as the air
v a l v e s , exhaust diaphragm, O-rings and rubber
pressure beneath the piston equals the effort ex-
graduating spring be replaced if they show signs of
erted by the drivers foot on the treadle or pedal on
wear or deterioration.
the upper portion, and the air above the outer relay
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