What standards and design criteria are there for the correct installation of safety valve vent pipes?
The standard on the specification for safety valves for steam and hot water in the United Kingdom is BS 6759:Part 1:1984, with amendments in 1987 to clause 2.4 and B.5. Sections B.3, B.4, and B.5 are relevant to the discharge pipework. Basically, the following points are made: The discharge pipe must not be smaller in diameter than the valve outlet. No undue stresses should be imposed on the installation which may cause distortion and leakage. For steam systems, the discharge pipe should rise from the outlet, and a small bore drain should be provided at any point where water could collect. The discharge pipe should be sized so that built-up back pressure does not exceed 12% of the set pressure. In addition, it is sensible to ensure that any horizontal runs should have a downward gradient at least 1:100 away from the valve, and the overall length should be as short and direct as possible.
