Baker Hughes 13900 Series Maintenance Manual

Baker Hughes 13900 Series Maintenance Manual Manual pdf 10 page image

6 | BHGE© 2018 Baker Hughes, a GE c o mpany. All r ights r e serve d .V. Terminology for Safety Relief Valves• Accumulation: The pressure increase over the maximumallowable working pressure of the vessel during dischargethrough the POSRV, expressed as a percentage of thatpressure or in actual pressure units.• Backpressure: The pressure on the discharge side of thePOSRV: Built-up Backpressure: Pressure that develops at thevalve outlet as a result of flow, after the POSRV hasbeen opened. Superimposed Backpressure: Pressure in thedischarge header before the POSRV opens. Constant Backpressure: Superimposed backpressurethat is constant with time. Variable Backpressure: Superimposed backpressurethat will vary with time.• Blowdown: The difference between set pressure andreseating pressure of the POSRV, expressed as apercentage of the set pressure or in actual pressure units.• Cold Differential Set Pressure: The pressure at which thevalve is adjusted to open on the test stand. This pressurecorrects for backpressure when a pop action pilot’s ventis piped to the main valve outlet.• Differential Between Operating and Set Pressures:Valves in process service will generally give best resultsif the operating pressure does not exceed 90% of the setpressure. However, on pump and compressor dischargelines, the differential required between the operatingand set pressures may be greater because of pressurepulsations coming from a reciprocating piston. The valveshould be set as far above the operating pressure aspossible.• Lift: The actual travel of the disc away from the closedposition when a valve is relieving.• Maximum Allowable Working Pressure: The maximumgauge pressure permissible in a vessel at a designatedtemperature. A vessel may not be operated above thispressure or its equivalent at any metal temperatureother than that used in its design. Consequently, for thatmetal temperature, it is the highest pressure at whichthe primary pressure POSRV is set to open.• Operating Pressure: The gauge pressure to which thevessel is normally subjected in service. A suitable marginis provided between operating pressure and maximumallowable working pressure. For assured safe operation,the operating pressure should be at least 10% under themaximum allowable working pressure or 5 psig (0.34bar), whichever is greater.• Overpressure: A pressure increase over the set pressureof the primary relieving device. Overpressure is similarto accumulation when the relieving device is set at themaximum allowable working pressure of the vessel.Normally, overpressure is expressed as a percentage ofset pressure.• Pilot Operated Safety Relief Valve (POSRV): A pressurerelief valve in which the major relieving device iscombined with, and is controlled by, a self-actuatedauxiliary pressure relief valve.• Rated Capacity: The percentage of measured flow atan authorized percent overpressure permitted by theapplicable code. Rated capacity is generally expressed inpounds per hour (lb/hr) or kilograms per hour (kg/hr) forvapors, standard cubic feet per minute (SCFM) or cubicmeters per minute (m3/min) for gases, and in gallons perminute (GPM) or Liter/min (L/min) for liquids.• Relief Valve: An automatic pressure-relieving device,actuated by static pressure upstream from the valve. Arelief valve is used primarily for liquid service.• Safety Relief Valve (SRV): An automatic pressure-relievingdevice used as either a safety or relief valve, dependingupon application. The SRV is used to protect personneland equipment by preventing excessive overpressure.• Safety Valve: An automatic pressure-relieving deviceactuated by the static pressure upstream of the valve,and characterized by a rapid opening or “pop” action. It isused for steam, gas, or vapor service.• Set Pressure: The gauge pressure at the valve inlet, forwhich the relief valve has been adjusted to open underservice conditions. In liquid service, the inlet pressureat which the valve starts to discharge determines setpressure. In gas or vapor service, the inlet pressure atwhich the valve pops determines the set pressure.