UFC 3 -430-11
14 February 2001
5-2.1.1.4 Maintenance. Provide manual block and bypass valves around control
valves where practical to allow for control valve removal and servicing while the system
is operational. If a manual bypass is not provided then furnish the valve with a hand
wheel.
5-2.1.1.5 Location. Locate control valves at grade where practical. Install the control
valve near the operating equipment that has to be observed while in local manual
control.
5-2.1.2 Pressure Regulators. Use self-actuated regulators only where the operating
pressure is below 10.34 bar (150 psig) and where vari ations from the control point are
acceptable. Use pilot-operated pressure regulators where the operating pressure is
equal to or above 10.34 bar (150 psig), or where minimal variations from the control
setpoint are acceptable.
5-2.1.3 Solenoid Valves. Common uses for solenoid valves in a boiler plant include
the routing of instrument air to control devices and shutoff service.
Verify solenoid valve sizing to ensure that the valve or damper will open or
close within the specified amount of time. Port size might have to be increased to
ensure the proper actuation time.
Verify that the proper solenoid valve is used for the intended service. An
example of a critical service application is a pilot gas shutoff solenoid valve. Most
manufacturer catalogs i nclude checklists on items to be specified. Critical items
sometimes overlooked include type of fluid, shutoff and opening pressures, and line test
pressure.
5-2.2
Actuators. Use spring-loaded diaphragm type actuators where practical.
Springless operators and cylinder operators are acceptable only when spring -loaded
diaphragm type actuators cannot provide the desired performance.
Select the actuator so that the valve or damper that it controls will fail safe.
Fail safe is defined as lock in position or take a position (either open or closed) that will
result in the least upset.
Furnish a pressure gauge to show diaphragm loading pressure on actuators
that do not have a positioner. Furnish positioners for all automatically operated
dampers. Furnish positioners for all control valves in critical service and where the
variable, such as flow, has to be closely controlled. Specify that the positioner be
furnished with the control valve or damper instead of separate procurement. Provide
bypass switches and 3 pressure gauges (air supply, instrument loading, and diaphragm
pressure) for all positioners.
5-2.3
current to pneumatic converters (I/Ps) for pneumatic actuators with electronic control
signals. It is important that the I/P be matched to the valve or damper, as applicable.
5-2
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