UL 51-2018 pdf free download.Power-Operated Pumps and Bypass Valves for Anhydrous Ammonia, LP-Gas, and Propylene.
4 Undated References
4.1 Any undated reference to a code or standard appearing in the requirements of this standard shall be
interpreted as referring to the latest edition of that code or standard.
5 Glossary
5.1 For the purpose of this standard the following definitions apply.
5.2 BYPASS VALVE — A valve used on the discharge side of a pump which opens automatically at a predetermined differential pressure so as to direct part or all of the pump discharge back to the supply tank. It is either provided as part of a pump assembly (integral bypass valve), or it is a separate valve which is piped into the pump discharge system at the time of installation.
5.2.1 BYPASS VALVE WITH VARIABLE FLOW CONTROL — A bypass valve incorporating an integral flow control valve section operated by a handle or lever, designed to allow controlled increase of return flow through the bypass valve.
5.3 LIQUEFIED PETROLEUM GAS (LP-GAS OR LPG) — Any material having a vapor pressure not exceeding that allowed for commercial propane, as defined in Standard Specification for Liquefied Petroleum (LP) Gases, ASTM D1835, that is composed predominantly of the following hydrocarbons, either by themselves (excluding propylene) or as mixtures: propane, propylene, butane (normal butane or isobutane) and butylenes.
5.4 RELIEF VALVE — A recirculating valve which opens at a predetermined differential pressure to direct the pump discharge back to the intake side of the pump. When provided, it is included as part of the pump assembly.
CONSTRUCTION
6 Assembly
6.1 The construction of a pump or bypass valve shall be such that parts are capable of being assembled in the required manner after being dismantled to the extent needed for replacement of parts or for other care or servicing.
6.2 Screws or bolts used to attach parts which are detached for care or servicing of the pump or bypass valve shall be capable of holding upon the application of the torques indicated in Table 6.1 after removal and replacement.UL 51 pdf download.