BENDIX LQ-5 BOBTAIL RATIO VALVE Manuel - Page 4

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BENDIX LQ-5 BOBTAIL RATIO VALVE Manuel
FIGURE 6 - LQ-5
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BOBTAIL RATIO VALVE RELEASING:
TRACTOR-TRAILER MODE
When air pressure beneath the proportioning piston depletes
to less than approximately 8 psi, the valve spring is able to
seat the exhaust valve. The "initial delivery" spring keeps
the inlet open and allows air from the LQ-5
flow through the valve, out the supply and back to the brake
valve.
FIGURE 7 - LQ-5
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BOBTAIL RATIO VALVE BLENDING
BACK: TRACTOR-TRAILER MODE
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FIGURE 8 - LQ-5
BRAKE APPLICATION—LQ-5
BLENDING BACK
Service brake pressure enters the LQ-5
™
valve delivery to
and combines with the force of the blend back spring to
work against control pressure. When service pressure is
sufficiently high (see Figure 3), the total downward force
begins to overcome the upward force of control pressure on
the blend back piston. The blend back piston is forced into
contact with the proportioning piston. Both pistons now move
as one. Because of the added surface area of the blend
back piston, LQ-5
supply pressure increases. When the piston assembly
contacts its seat in the body, the LQ-5
application pressure. There is then a 1:1 ratio between
supply and delivery.

BOBTAIL MODE

BRAKE VALVE APPLICATION, BALANCE,
RELEASE
When the trailer supply valve is pulled out, air in the LQ-5
valve control port flows back to the trailer supply valve and
exhausts to atmosphere. With no control pressure, the blend
back piston is forced by its spring to contact the proportioning
piston. The inlet/exhaust valve is held by its spring and seals
the exhaust passage. Both pistons, now moving as one,
reach their stop in the body.
This is the position for bobtail mode apply, hold and release.
The LQ-5
™
BOBTAIL RATIO VALVE MODE
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valve delivery pressure "catches up" as
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valve delivers full service application pressure in
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VALVE
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valve supply port
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valve delivers full
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