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LOAD PISTON
RELAY PISTON
SUPPLY PORT
INLET/EXHAUST
VALVE
FIGURE 3 - CHARGING
LOAD PISTON
RELAY PISTON
SUPPLY PORT
INLET/EXHAUST
VALVE
FIGURE 4 - NORMAL (RAPID) APPLICATION
NORMAL (RAPID) APPLICATION
Figure 4 shows an R-12P
service brake application. "Normal" means the control
signal is applied rapidly enough to build up pressure on
the relay piston and "open" the inlet valve, causing the
™
R-12P
valve to react like a relay valve. The relay piston
opens the inlet, allowing supply air to fl ow out the delivery
port to the next valve in the system.
CONTROL
PORT
DELIVERY
PORT
CONTROL
PORT
™
valve receiving a "normal"
Note that these events occur quickly, due to the "preload"
on the relay piston. This preload, provided by supply air
pressure acting on the load piston, is a feature unique to
the R-12P
™
valve.
BALANCE
Air pressure being delivered by the open inlet valve is
also effective underneath the R-12P
When air pressure beneath the piston approaches control
pressure on top of the piston, the piston and inlet valve lift
together and close the inlet valve. The exhaust remains
closed, and the valve achieves "force balance." That is,
the piston and inlet/exhaust valve are in their neutral
state. This is the position commonly known as "balanced"
when referring to conventional relay valves. However,
conventional relay valves cannot achieve true air pressure
balance because of their inherent differentials. The R-12P
valve achieves this balance because of its equalizing
orifi ce. The orifi ce allows control pressure and delivery
pressure to be "common" and equalize. In this position,
shown in Figure 5, sustained service brake applications
can be held, with no "residual" differential.
EQUALIZING
ORIFICE
PROVIDES AIR
PRESSURE
BALANCE
SUPPLY PORT
INLET/EXHAUST
VALVE
FIGURE 5 - BALANCE
™
valve relay piston.
LOAD PISTON
RELAY
PISTON
CONTROL PORT
DELIVERY
PORT
™
3
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