UL 331

1 Scope
1.1 These requirements cover complete, self-contained strainer or filter assemblies intended for use with designated flammable fluids and anhydrous ammonia (fertilizer grade) in residential and commercial fuel-burning, dispensing, and handling facilities. Although these devices are designated strainers, they may be either strainers or filters according to the common terminology of the industry.

1.2 The term flammable fluids as used in this standard means fuel oil, gasoline, kerosene, and similar petroleum products, liquefied petroleum gas (LP-Gas), and manufactured and natural fuel gas.

1.3 These requirements do not cover the following:
a) Strainers for handling liquids under cryogenic conditions;
b) Strainers for marine use;
c) Strainers for automotive fuel lines;
d) Strainers for handling refrigerants;
e) Strainers for use in such facilities as chemical, petrochemical, petroleum, and utility power plants; and
f) Strainers for use in fluid-power (hydraulic and pneumatic) applications.

1.4 Requirements for non-potable water strainers are covered in Supplement SA.