Ross Controls 3_2 VALVES SERIES DM2 D - Manual (Page 8)

Valve de-actuated:
The flow of inlet air pressure
into the crossover passages
is restricted by the size of the
passage between the stem and
the valve body opening. Flow is
sufficient to quickly pressurize
pilot supply/timing chambers A
and B. The inlet poppets prevent
air flow from crossover passages
into the outlet chamber. Air pres-
sure acting on the inlet poppets
and return pistons securely hold
the valve elements in the closed
position. (Air passages shown
out of position and reset adapter
omitted for clarity.)
Valve actuated:
Energizing the pilot valves
simultaneously applies pres-
sure to both pistons, forcing the
internal parts to move to their
actuated (open) position, where
inlet air flow to crossover pas-
sages is fully open, inlet poppets
are fully open and exhaust pop-
pets are fully closed. The outlet
is then quickly pressurized, and
pressure in the inlet, crossovers,
outlet, and timing chambers are
quickly equalized.
De-energizing the pilots quickly
causes the valve elements
to return to the ready-to-run
position.
Valve loked-out:
Whenever the valve elements
operate in a sufficiently asynchro-
nous manner, either on actuation
or de-actuation, the valve will
move to a locked-out position.
In the locked-out position, one
crossover and its related timing
chamber will be exhausted, and
the other crossover and its related
timing chamber will be fully pres-
surized. The valve element (side
B) that is partially actuated has
pilot air available to fully actuate
it, but no air pressure on the
return piston to fully de-actuate
the valve element. Air pressure
in the crossover acts on the dif-
ferential of side B stem diameters
creating a latching force.
Side A is in a fully closed position, and has no pilot air available to
actuate, but has full pressure on the inlet poppet and return piston
to hold the element in the fully closed position.
Inlet air flow on side A into its crossover is restricted, and flows
through the open inlet poppet on side B, through the outlet into the
exhaust port, and from the exhaust port to atmosphere. Residual
pressure in the outlet is less than 1% of inlet pressure.
The return springs are limited in travel, and can only return the valve
elements to the intermediate (locked-out) position. Sufficient air
pressure acting on the return pistons is needed to return the valve
elements to a fully closed position.
Resetting the valve:
The valve will remain in the locked-
out position, even if the inlet air
supply is removed and re-applied. A
remote reset signal (air or electric),
or a manual push button actuation
must be applied to reset the valve.
Reset is accomplished by mo-
mentarily pressurizing the reset
port. Actuation of the reset piston
physically pushes the main valve el-
ements to their closed position. Inlet
air fully pressurizes the crossovers
and holds the inlet poppets on seat.
Actuation of the reset piston opens
the reset poppet, thereby, immedi-
ately exhausting pilot supply air, thus, preventing valve operation
during reset. (Reset adapter added to illustration.)
De-actuation of reset pistons
causes the reset poppets to
close and pilot supply to fully
pressurize.
Reset air pressure can be
applied by a remote 3/2 normally
closed valve, or from an optional
3/2 normally closed solenoid, or
a manual push button mounted
on the reset adapter.
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 inlet pressure is removed. This device
is not part of the valve lockout function,
but, rather, only reports the status of
the main valve.
Size 12 and 30 valves require relatively
large pilots to actuate and de-actuate
the main valve elements. In order to
achieve extremely quick valve response
for such large pilots, a 2-stage solenoid
pilot system is incorporated into the
design. This keeps the electrical
current required to operate the pilots,
to a minimum.
Overview of DM 2® Series D Double Valve Function
EXHAUST T T T T
INLET
OUTLET
EXHAUST
OUTLET
INLET
A B
EXHAUST T T T T
INLET
OUTLET
EXHAUST
OUTLET
INLET
A B
EXHAUST
OUTLET
INLET
A B
A B
EXHAUST T T T T
INLET
OUTLET
EXHAUST
OUTLET
INLET
A B
Status indicator (optional)
in normal ready-to-run position
Valve actuated
Valve ready-to-run
Valve locked out
Valve being reset
Size 12 & 30 pilots
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