UL 51-2013 pdf 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. 5.3 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 D1 835, 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.
11 Pumps and Bypass Valves Pressure Ratings 1 1 .1 A bypass valve or pump shall have a service pressure rating not less than that shown in Table 1 .1 , in accordance with the differential pressure produced at specific flow capacity through the pump or valve when tested in accordance with the Differential Pressure Test, Section 1 9. 1 1 .2 A bypass valve shall provide for connection of piping for returning the recirculated liquid back to the supply or storage tank. 1 1 .3 After the bypass valve is adjusted as intended, it shall be locked or sealed to reduce the risk of tampering; or the adjusting means shall be such that the maximum adjustment obtainable will not permit a differential pressure in excess of the differential at specified flow capacity, and service pressure rating for the valve in accordance with Table 1 .1 . 1 1 .4 The use of a lock nut on an adjusting screw or a threaded cap over the adjusting screw is judged to be in compliance with the locked or sealed requirement in 1 1 .3. 1 1 .5 A pump shall be marked in accordance with 25.2 when a bypass valve is not provided as part of a pump assembly and the pump is capable of developing a differential pressure in excess of 1 25 psi (1 00 psi for propylene service). 1 1 .6 When a bypass valve for anhydrous ammonia or LP-Gas has a differential pressure rating in excess of 1 25 psi, it shall carry a caution tag as outlined by 25.6. When a bypass valve for propylene has a differential pressure rating in excess of 1 00 psi, it shall carry a caution tag as outlined by 25.6.