SAFETY VALVE
an automatic pressure relieving device actuated by the static pressure upstream of the valve, and characterized by rapid full opening or pop action. Used for steam, gas or vapor service.
SAFETY RELIEF VALVE
an automatic pressure actuated relieving device suitable for use as either a safety of relief valve, depending on the application.
MAXIMUM ALLOWABLE WORKING PRESSURE
the maximum gage pressure permissible in the top of a completed vessel in its operating position for a designated temperature. This pressure is based on calculations for each element in a vessel using nominal thicknesses, exclusive of allowance for corrosion and thicknesses required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving protecting the vessel. The design pressure may be used in place of maximum allowable working pressure in cases where calculations are not made to determine the valve of the latter.
COLD DIFFERENTIAL TEST PRESSURE
in pounds per square inch gage is the inlet static pressure at which the pressure relief valve is adjusted to open on the test stand. This pressure includes the correction for service conditions of back pressure or temperature. or both
BUILT-UP BACK PRESSURE
Pressure existing at the outlet of a pressure relief device occasioned by the ow through that particular device into a discharge system
SUPERIMPOSED BACK PRESSURE
the static pressure existing at the outlet of a pressure relief device at the time the device is required to operate. it is the result of pressure in the discharge system from other sources.
BACK PRESSURE
the static pressure existing at the outlet of a pressure relief device due to pressure in the discharge system.
SET PRESSURE
in pounds per square inch gage, the inlet pressure at which the pressure relief valve is adjusted to open under service conditions. In a safety or safety relief valve in gas, vapor or steam service, the set pressure is the inlet pressure at which the valve pops under service conditions. In a relief or safety relief valve liquid service, the set pressure is the inlet pressure at which the rst steady steam ows from the valve perpendicular to the outlet.
RELIEF VALVE
an automatic pressure relieving device actuated by the static pressure upstream of the valve, which opens in proportion to the increase in pressure over the opening pressure.
PRESSURE RELIEF VALVE
a pressure relief device designed to re-close and prevent the further ow of uid after normal conditions have been restored.
OPERATING PRESSURE
the pressure, in pounds per square inch gage to which the vessel is usually subjected in service. A vessel is usually designed for a maximum allowable working pressure, in pounds per square inch gage, which will provide & suitable margin above the operating pressure in order to prevent any undesirable operation of the relief device. It is suggested that this margin be as great as possible consistent with economical vessel and other equipment design, system operation and the performance characteristics of the pressure relieving device.
ACCUMULATION
the pressure increase over the maximum allowable working pressure of the vessel during discharge through the pressure relief valve, expressed as a percent of that pressure or in pounds per square inch.
OVER PRESSURE
a pressure increase over the set pressure of a pressure relief valve, usually expressed as a percentage of the set pressure.
BLOW DOWN
the difference between actual popping pressure of a pressure relief valve and actual reseating pressure, expressed as a percentage of set pressure or in pressure units.
LIFT
the actual travel of the disc away from closed position when a valve is relieving
DIFFERENTIAL SET PRESSURE
the pressure differential, in pounds per square inch between the set pressure and the constant superimposed back pressure. It is applicable only when it is conventional type safety valve is being used in service against a constant superimposed back pressure.