ENGINEERING FLUIDS DIAGRAMS AND PRINTS
Engineering Fluid Diagrams and Prints
Some valves are provided with actuators to allow remote operation, to increase mechanical
advantage, or both. Figure 2 shows the symbols for the common valve actuators. Note that
although each is shown attached to a gate valve, an actuator can be attached to any type of valve
body. If no actuator is shown on a valve symbol, it may be assumed the valve is equipped only
with a handwheel for manual operation.
The combination of a valve and an actuator is commonly called a control valve. Control valves
Figure 2 Valve Actuator Symbols
are symbolized by combining the appropriate valve symbol and actuator symbol, as illustrated
in Figure 2. Control valves can be configured in many different ways. The most commonly
found configurations are to manually control the actuator from a remote operating station, to
automatically control the actuator from an instrument, or both.
In many cases, remote control of a valve is accomplished
Figure 3 Remotely Controlled Valve
by using an intermediate, small control valve to operate
the actuator of the process control valve.
intermediate control valve is placed in the line supplying
motive force to the process control valve, as shown in
Figure 3. In this example, air to the process air-operated
control valve is controlled by the solenoid-operated,
3-way valve in the air supply line. The 3-way valve may
supply air to the control valve's diaphragm or vent the
diaphragm to the atmosphere.