UL 331:2017 pdf free download – STANDARD FOR SAFETY Strainers for Flammable Fluids and Anhydrous Ammonia.
8.5 A flat gasket employed with a bolted cover shall be cemented to the cover or body unless the construction is such that the gasket will be retained by either the body or cover when the cover is removed.
Exception: Cementing or retaining of the gasket is not necessary provided a complete set of new gaskets is furnished with each replacement cartridge for a strainer that employs a cartridge-type filtering element.
8.6 A plant fiber gasket shall not be less than 1/32 inch (0.8 mm) thick.
8.7 A cork gasket shall be graphited on one side, and when high pressures are involved, the other side shall be cemented in place so the gasket will not be blown out.
9 Stuffing Boxes
9.1 If packing is used to prevent leakage around a stem, and the construction is such that it is necessary for the user to adjust or renew the packing during usage or as wear occurs, a stuffing box complying with the requirements in 9.2 — 9.8 shall be provided.
9.2 A stuffing box shall be provided with a removable, shouldered, unthreaded follower gland, and shall have a nut or other means for adjusting the gland to maintain pressure on the packing.
9.3 A stuffing box gland shall be made of corrosion-resistant material.
9.4 A stuffing box shall be fully packed prior to shipment of the strainer.
9.5 A spring-loaded follower gland shall employ a spring made of corrosion-resistant material, or of material provided with a corrosion-resistant protective coating.
9.6 If corrosion of a stem will cause damage to a packing or seal material and result in leakage, the stem shall be of a corrosion-resistant material.
9.7 A stem shall be constructed so that it cannot be completely withdrawn from the strainer by reverse rotation. Threads of a stem shall not enter a stuffing box recess.
9.8 A stem shall be of sufficient length to permit repacking the stuffing box without requiring the strainer to be dismantled.
10 Springs
10.1 The construction and application of a spring employed in a strainer shall be such that it is not likely to fail because of corrosion, fatigue, overstress, or wear, if failure of the spring will allow the strainer elements to become displaced.
PERFORMANCE
11 General
11.1 Except as otherwise indicated, representative samples of a strainer are to be subjected to the tests described in Sections 12 — 18.
11 .2 If a series of strainers is to be investigated in which the bodies differ in size only, three representative samples are to be chosen to include the largest, smallest, and one intermediate size. If a strainer having a single body size is being investigated, one sample is sufficient.
11.3 A strainer is to be investigated for a specific fluid or fluids and for the service conditions for which it is to be recommended, such as fluid temperature and fluid pressure.
12 Tests On Synthetic-Rubber Parts
12.1 A synthetic-rubber part in contact with one of the fluids specified in Table 12.1 shall not show excessive volume change or loss of weight as specified in 12.3, when considered on the basis of its intended function, following immersion in the specified test fluid in accordance with the requirements in the Standard for Gaskets and Seals, UL 157.