AS 1271:2003 pdf – Safety valves, other valves, liquid level gauges and other fittings for boilers and unfired pressure vessels

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AS 1271:2003 pdf – Safety valves, other valves, liquid level gauges and other fittings for boilers and unfired pressure vessels

AS 1271:2003 pdf – Safety valves, other valves, liquid level gauges and other fittings for boilers and unfired pressure vessels.
3.1 GENERAL
3.1.1 Scope of section
This Section specifies requirements for safely and relief valves.
NOTE: Any reference to safety valves includes relief valves.
3.1.2 Fail-safe
Each safety valve shall be designed and constructed so that failure of any part will not obstruct the free and full discharge from the valve.
3.1.3 Stem seals
The stern of a safety valve shall not be fitted with a stuffing box. non-metallic bushing or ‘0’ ring seal.
3.1.4 Locking of adjustments
Any setting that is adjustable. e.g. blowdown, relieving pressure, and the like, shall be provided with a device that is sufficiently positive to prevent subsequent movement through accident, vibration, or expansion. Means for sealing, locking, or other protection from interference shall he provided as required by the particular application Standard.
3.1.5 Drainage
Application Standards, in general. require that a means of drainage be provided at the lowest point on the discharge side of a safety valve system. Where possible, this should he provided in the body of the valve.
3.1.6 Freedoni of operation
The design of safety valves and the choice of their materials of construction shall take into consideration the possible effect on the freedom of the operation of differential expansion and contraction, discharge reaction, icing of external components during discharge. and of gumming or deposits. Valves with plain flat discs without bottom guides shall be used where gumming or deposits arc probable on the inside. The valve spring should be protected by a suitable seal. e.g. a bellows, where it is liable to corrosion or blockage due to products discharged. or be suitably shielded where it is liable to corrosion or blockage due to the environment.
3.2 SPRING LOADING
3.2.1 Springs
3.2.1.1 Design
The design calculations for springs shall be to an approved method. e.g. BS 1726-I. for helical compression springs.
3.2.1.2 Workmanship
Each end of a helical compression spring shall present a flat bearing of not less than
75 percent of the circumference at right angles to the axis, so that, when placed on end on a
horiiontal plane, the spring will he within the tolerances recommended in Appendix A of
BS 1726-I for class A springs.
NOTE: If it is necessary to specify tolerances closer than those recommended in BS 1726-I, arrangements should be made between the valve manufacturer and the spring manufacturer.