Pressure relief valves
7.—(1) A pressure relief valve which is fitted to a part of a gas system (including a gas container) shall—
(a)be made entirely of suitable metal and so constructed and fitted as to ensure that the cooling effect of the gas during discharge shall not prevent its effective operation,
(b)be capable, under the most extreme temperatures likely to be met (including exposure to fire), of a discharge rate which prevents the pressure of the contents of the gas system from exceeding its design pressure,
(c)have a maximum discharge pressure not greater than the design pressure of the gas container,
(d)be so designed and constructed as to prevent unauthorised interference with the relief pressure setting during service, and
(e)have outlets which are—
(i)so sited that so far as is reasonably practicable in the event of an accident the valve and its outlets are protected from damage and the free discharge from such outlets is not impaired, and
(ii)so designed and constructed as to prevent the collection of moisture and other foreign matter which could adversely affect their performance.
(2) The pressure at which a pressure relief valve is designed to start lifting shall be clearly and permanently marked on such valve.
(3) A pressure relief valve which is fitted to a gas container shall communicate with the vapour space in the gas container and not with any liquefied gas.