Single OffsetThe centre of rotation is moved back from the centreline of the valve disc. The seat and seal are designed conically and on centre.This design relies on a frictional interference seal and so is applicable only to soft seated valves

Double OffsetThe centre of rotation is moved from the centreline of the valve body. The seat and seal are design remains conical and on centre. This design again relies on a frictional , interference seal, but the length of rotation over which this friction occurs Is reduced, allowing a larger of process resistant seal materials to be used. However these materials must be relatively soft or highly elastic to prevent "jamming

Triple OffsetThe centreline of the cone is ritated away from the valve centreline resulting in an ellipsodal profile and providing the third offset. With this geometry, seat seal interference is completely eliminated ensuring long sealing life. The result is a torque seated, process pressure aided FRICTIONALESS seal. The geometry allows the body seat to be used as the closed limit stop, aiding operator adjustment. The Triple Offset design is ideally suited to metal seated valves providing bubble-tight performance on high temperature, high pressure and firesafe applications

Valve typeCommon test standardSteel gates, globes and checksAPI 598Cast Iron gatesAPI 598, MSS SP-70*Bronze gates, globes and checksMSS SP-80*Pressure seal valvesASME B16.34*Steel valves larger than NPS 24ASME B16.34*Pipeline valvesAPI 6D*Cast iron globesAPI 598, MSS SP-85*Cast iron checksAPI 598, MSS SP-71*Cast iron plugsAPI 598, MSS SP-78*Steel ball valvesAPI 598Steel butterfly valvesAPI 598Cryogenic valvesBS 6364, API 598Pressure relief valvesASME PTC 25, API 527Control valvesISA-S75, FCI 70-2

API 598, Valve Inspection and Test Widely used test specification around the world. It covers all types of valves in sizes through NPS 24. It includes leakage rates and testing criteria for metal-seated and resilient-seated valves.API 527, Seat Tightness of Pressure Relief Valves Covers the seat tightness of pressure relief valves. It also includes allowable leakage rates for testing with steam, water and air.ASME B16.34, Valves Flanged, Threaded and Welding End The primary valve design document, it also contains charts for determining the working pressures of valves to be used in conjunction with other test standards, such as API 598. B16.34 contains a test procedure, but no seat leakage acceptance criteria.ASME PTC 25, Pressure Relief Devices Reference document for the testing of PRVs, contains detailed procedures for testing relief valves with air/ steam.FCI 70-2, Control Valve Seat Leakage It contains detailed test procedures and leakage rate classes for control valves. The leakage classes are also occasionally referenced by other documents and used as acceptance criteria.ISA-S75, Hydrostatic Testing of Control Valves It provides a procedure for the hydrostatic shell testing of control valves. Closure testing and acceptance criteria are out of the scope of this document and usually are covered by referencing FCI 70-2.ISO 5208, Industrial Valves, Pressure Testing of Valves ISOs primary testing standard, this document covers all types of valves and has four levels of allowable closure test leakage.

MSS SP61, Hydrostatic Testing of Steel Valves Similar to API 598, But has some subtle differences in test holding times and leakage rates.MSS SP70, Cast Iron Gate Valves, Flanged and Threaded Ends Primary design document. it also contains testing procedures and acceptance criteria.MSS SP71, Cast Iron Swing Check Valves, Flanged and Threaded Ends Primary design document ,also contains testing procedures and acceptance criteria.MSS SP78, Cast Iron Plug Valves, Flanged and Threaded End Primary design document ,also contains testing procedures and acceptance criteria.MSS SP80, Bronze Gate, Globe, Angle and Check Valves Primary design document ,also contains testing procedures and acceptance criteria.MSS SP85, Cast Iron Globe & Angle Valves Primary design document, also contains testing procedures and acceptance criteria.

The primary goal of PRV testing is to confirm that the valve will both lift (open) at the correct pressure and provide the prescribed rate of flow. A control valve is normally tested to measure its rate of flow as well. Both PRVs and control valves are also tested to confirm the integrity of their pressure envelope.PRVs are tested in accordance with two primary standards: ASME PTC 25, Pressure Relief Devices and API 527, Seat Tightness of Pressure Relief Valves. The common testing standards for control valves are ISAthe Instrumentation, Systems and Automation Society of America ISA-S75.19 and Fluid Controls Institute (FCI) FCI 70-2, Control Valve Seat Leakage.The upstream pipeline and petroleum valve industry also have their own testing specification. It is located within the pages of the API 6D, Pipeline Valves valve design document. API 6D leakage rates are very close to those of API 598, but its holding times are longer.

Hydro tests and Pneumatic TestsFugitive Emission & Helium Leak TestsCryogenic TestsFire TestsHot & Cold Cyclic TestsSeismic TestsNatural Frequency TestsStatic Load SimulationPipe End Reaction Tests

Two basic types of valves:Operating valves these are valves that are used a lotBlock valves seldom operated; serve to block flow through pipe when needed such as during maintenance or shut-down of plant or pipe line.Valve Locations Hand-operated valves should be located first, then locate auto valvesHand-operated valves should be located for access ways and maintenance areasDrain valves should be located near valves where trapped fluid may be removed Operating valves more than 7-6 above grade or platform MUST have a chain operator. Use of chain operators or manual actuators should be limited Important valves should be easily accessible for operation, repair & replacementControl valves should be located at or near grade or platform level All valves should be located outside of pipe racks

The most common valve design standard for the past 50 years has been the American Petroleum Institute (API) valve standard for refinery use, known today as API 600, Bolted Bonnet Steel Gate Valves for Petroleum & Natural Gas Industries. For 20 years, the document also contained valve testing criteria, and that criteria was pretty tough: Valves shall show no leakage when subjected to a hydrostatic (or air) seat test. Today, most valve manufacturers strive for and achieve a zero closure test leakage rate during initial factory testing of their metal seated gate and globe valves. However, the predominant valve testing standard, API 598, Valve Inspection and Test, does have allowable leakage rates for these types of valves in sizes above NPS 2. Virtually all test specifications for resilient-seated valves require they exhibit zero leakage during the test period. ISO 5208 is similar to the API 598 document,One of the key differences between them is- ISO document has a choice of four leakage rates, from gross leakage to zero. The ISO document also widens the users vocabulary by one wordobturator. An obturator is the closure element of a valve and in the ISO document it replaces the term disc or wedge.Another difference in many ISO valve standards is that they also include testing criteria within their base design document. This has not been the case for the past 40 years for most steel and alloy valves in the United States. However, there is more and more talk at standards development meetings about adding test criteria to design specifications, such as many of the API valve standards. While steel valve specifications such as API 600 have yet to be augmented with testing criteria, there are several U.S. valve standards that do have self-contained testing procedures. These are primarily iron and bronze valve standards and are covered by a host of Manufacturers Standardization Society (MSS) documents.