Ross Controls CATEGORY 4 - 3_2 VALVES SERIES DM2 C, E - Manual (Page 7)

Overview of DM 2® Series E Double Valve Function
Valve de-actuated
(ready-to-run):
The flow of inlet air pressure into
the crossover passages from the
inlet chamber is restricted by
orifices that allow air pressure to
bypass the lower inlet poppets.
Flow is sufficient to quickly
pressurize the pilot supply/timing
chambers on both sides A and B.
The upper inlet poppets prevent
air flow from the crossover
passages into the outlet chamber.
Air pressure acting on the inlet
poppets and return pistons
securely hold the valve elements
in the de-actuated position. (Air
passages shown out of position
for clarity.)
Valve actuated:
Energizing the pilot solenoids
simultaneously applies pressure
to both pistons, forcing the
internal parts to move to their
actuated position, where inlet
air flow to outlet is open and
both exhaust poppets are
closed. The outlet is then quickly
pressurized, and pressure in
the inlet, crossovers, outlet, and
timing chambers are quickly
equalized. De-energizing the
main solenoids causes the valve
elements to return to the ready-to-
run (de-actuated) position.
Valve locked-out:
Whenever the valve elements
operate in a sufficiently
asynchronous manner, either
on actuation or de-actuation,
the valve will shift into a locked-
out position. In the locked-out
position, one crossover and its
related timing chambers will
be exhausted, and the other
crossover and its related timing
chambers will be pressurized.
The valve element (side A) that
is partially actuated has pilot air
available to actuate it, but there
is no air pressure on the return
piston to de-actuate that valve
element. Air pressure in the
crossover acts on the differential of side A stem diameters
creating a latching force.
Side B is in the de-actuated position, but has no pilot air available
to actuate with and has full pressure on its upper and lower
inlet poppets and return piston to hold it in place. Inlet air flow
on side B into its crossover is restricted and flows through the
open upper inlet poppet on side A, through the outlet into the
the exhaust port, and from the exhaust port to atmosphere.
Residual pressure in the outlet is less than 1% of inlet pressure.
Also, the return springs can only return the valve elements to the
intermediate (locked-out) position. Therefore, the valve will remain
in the locked-out position even if the inlet air supply is removed
and re-applied. A reset signal must be applied intentionally in
order to reset the valve.
Resetting the valve:
Reset is accomplished by
momentarily energizing the
reset solenoid. Actuation of
the reset solenoid provides
inlet air pressure to the reset
pistons which physically push
the main valve elements to
their de-actuated position. Inlet
air pressurizes the crossovers
and volume chambers, thereby
applying air to the return pistons
which then hold the upper inlet
poppets on seat. De-actuation
of the reset solenoid removes
pressure from the lower side of
the reset pistons, thus allowing
them to return to their de-
actuated position.
Reset anti-tie-down feature:
Attempting to energize the valve’s main solenoids while the reset
solenoid is energized will cause side B to shift (overcoming the
pressure on the small reset piston), but side A will not move
due to the pressure on the larger reset piston on that side. This
will cause the valve to go into and remain in the locked-out
position until a reset signal is applied while the main solenoids
are de-energized.
Status indicator:
The status indicator pressure
switch will actuate when
the main valve is operating
normally, and will de-actuate
when the main valve is in the
locked-out position or when
inlet pressure is removed.
This device is not part of the
valve lockout function, but,
rather, only reports the status
of the main valve.
A B
EXHAUST
OUTLET
INLET
.004.004 .004
A B
EXHAUST
OUTLET
INLET
A B
EXHAUST
OUTLET
INLET
Valve being reset.
Status indicator in normal
ready-to-run position.
Valve locked-out.
Valve actuated.
Valve ready-to-run.
A B
EXHAUST
OUTLET
INLET
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