UL 51 PDF

1 Scope

1.1 These requirements cover power-operated pumps and bypass valves for use in liquid transfer operations in non-refrigerated systems in installations for:

1. a) Anhydrous ammonia systems installed in accordance with the Safety Requirements for the Storage and Handling of Anhydrous Ammonia, CGA/GAS G-2.1 (ANSI K61.1);

2. b) Liquefied petroleum gas (LP-Gas) systems installed in accordance with the Liquefied Petroleum Gas Code, NFPA No. 58; and

3. c) Propylene systems.

1.2 These requirements do not cover:

1. a) Pumps or compressors intended for handling anhydrous ammonia or LP-Gas or propylene in the gaseous phase and

2. b) Pumps, compressors or bypass valves for anhydrous ammonia, LP-Gas, or propylene for use in chemical, petro-chemical, petroleum, or utility power plants; nor pipeline or marine terminals; nor related storage facilities at such plants or terminals.

1.3 Equipment covered by these requirements is for use with LP-Gas, propylene, or anhydrous ammonia as covered by the Standards and Codes in 1 and shall have a minimum service pressure rating in accordance with .

Exception: A pump without an integral bypass valve with a higher differential pressure obtained in the Differential Pressure Test, Section 20, is permitted to have a lower minimum service pressure rating if it is marked in accordance with 2.

Maximum differential pressure produced when subjected to the Differential Pressure Test, Section 20

Anhydrous ammonia and LP-Gas equipment minimum service pressure rating

Propylene equipment minimum service pressure rating

psig (kPa)

psig (kPa)

psig (kPa)

≤ 100 (689) Propylene equipment only

Not applicable

350 (2415)

≤ 125 (862)

350 (2415)

375 (2585)

>125 (863) ≤ 150 (1034)

375 (2586)

400 (2758)

>150 (1034) ≤ 200 (1379)

400 (2758)

425 (2930)

≥ 200 (1379)

200 + differential pressure produced (1379 + differential pressure produced)

225 + differential pressure produced (1551 + differential pressure produced)

Summary of Topics

This Eleventh Edition of ANSI/UL 51 dated May 15, 2023 is being issued to update, correct, and clarify requirements.