A POL valve (originally for Prest-O-Lite) is a gas connection fitting used on liquefied petroleum gas (LPG) cylinders.
The oldest standard for such connections, it was developed by the Prest-O-Lite company, hence the name.[1] It is still the most common such fitting in some countries such as Australia.[1] All 4.5 kg and 9 kg gas cylinders in Australia use a POL valve. There are an estimated 9 million 9 kg cylinders with the Type 21 (POL) valve and cylinder connection in circulation across Australia. In this market, the cylinders mostly supply gas to consumer owned barbecues and patio heaters.[2]
POL valves are legal and quite common in the United States, especially on larger containers, although certain uses (smaller portable containers) require a modified version of the POL valve that includes some safety features.
In making the connection, a male connector is screwed into the Type 21 valve. The first male connectors relied on a metal to metal connection (brass on brass) with sufficient pressure applied via a hexagon nut to achieve an effective seal. The hexagon nut required a spanner to achieve sufficient pressure to obtain a gas tight seal. The notched hexagon nut denotes it is a left-hand thread. Following international convention, the standard changed to allow the use of an integrated hand wheel, with leak tightness being provided by an o-ring or rubber bull nose.[2]
Thread Type
editPOL is the common name for the standard CGA 510 (US Compressed Gas Association connection number). The Thread specification is .885" – 14 NGO – LH – INT, meaning 0.885 in (22.5 mm) diameter thread, 14 threads per inch (1.814 mm pitch), National Gas Outlet form, left-hand internal thread.[3] This thread is also referred to as "Type 21" as per the Australian standard AS2473.2.[4] In summary, POL, CGA 510 and Type 21 all refer to the same specification.
See also
editReferences
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