Aventics PD-4, Service Information

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“PD” Relay Valve
Service Information
SM-400.8004
The “PD” Relay Valve reduces the required capacity
and size of the control lines. The relay valve also
eliminates the delay normally caused by exhausting
the air back through long lines.
WARNING: INSTALLATION and MOUNTING
The user of these devices must conform to
all applicable electrical, mechanical, piping and other
codes in the installation, operation or repair of these
devices.
INSTALLATION! Do not attempt to install, oper-
ate or repair these devices without proper train-
ing in the technique of working on pneumatic or
hydraulic systems and devices, unless under
trained supervision. Compressed air and hydrau-
lic systems contain high levels of stored energy.
Do not attempt to connect, disconnect or repair
these products when a system is under pressure.
Always exhaust or drain the pressure from a sys-
tem before performing any service work. Failure
to do so can result in serious personal injury.
MOUNTING! Devices should be mounted and
positioned in such a man
n
er that they cannot be
accidentally operated.
The “PD” Relay Valve functions to relay or repeat con-
trol pressure signals with large quantities of air at cor-
responding pressures. Used in systems where long
lines are required from the control device to the receiv-
ing device, the PD4 Relay Valve permits fast system
response by reducing control pressure transmission
times. A direct local connection is made possible,
through the Relay Valve, between a supply source and
the receiving device. This reduces the required capac-
ity and size of the controlling device and the size of the
control line. When control pressure is reduced or re-
leased, a local exhaust of pressure from the receiving
device, through the Relay Valve, eliminates the delay
normally caused by exhausting the air back through
the long control line.
CONSTRUCTION
The “PD” Relay Valve is corrosion resistant with an
anodized aluminum valve body and operator castings.
The balanced spool valve is stainless steel. Triple
supported, oil-resistant seals give a tight closure and
long life protection. The large spring-opposed piston is
also cast aluminum and has an “O” ring seal. The
spring and various other parts are cadmium plated.
OPERATION
Control pressures applied to the top of the control piston
positions a spool valve to allow inlet pressure to flow to the
outlet port. This outlet pressure, in addition to flowing to
the receiving device, flows to the underside of the control
piston through the external copper tubing connection.
When the outlet pressure balances the applied control
pressure, the spool valve is returned by a spring to close
the connection between inlet and outlet. Air pressure re-
quirements of the receiving device automatically cause the
control piston to function to maintain pressure in the outlet
line, either increasing or decreasing to an amount corre-
sponding to the control pressure, under varying operating
conditions.