Safety Valve Popup

The valve will still lift at 600psig.

It is better to lower the water level to normal using the blowdown facility so as to place the boiler in its normal operating condition, rather than blow the water out of the safety valve!

Dear PWslack ,

we are steaming boiler only for process application. actually boiler is in cold condition ,we want to keep it ready for our emergency light up if required. Thus we want to hold drum water pressure on 400- 350 psig . if we are raising the pressure then water is passing through safety valve but safety valve is set to pop up on 600 psig of steam .

basically I want to know why water is passing through safety valve on 400 or 350 psig.

Water doesn't compress, steam does. The safety valve is designed for steam...........not water. Think of a pressure cooker pot with the weight on the top. When enough steam pressure builds, it will lift the weight and release steam. If you filled the pot with water all the way up to the release weight, it will find it's way out.

I think you are somehow overfilling your drum. Water shouldn't be in contact with the safety valve.

I guess you could have a bad relief valve, but I still wouldn't let water get in it if it's meant for steam.

The water level should never be that high, otherwise priming will ensue.

Theoritically yes safety valve should hold the pressure but practically it do not. In case of steam drum over flow in cold condition it has been observed that bench tested safety valves starts passing. It may be because of water hammer caused by the steam forming in pockets within the steaming circuit or may be water hammer caused by the water wall turbulances.

There may be a water hammer scenario involved here. Even though the pressure seems to be only 400 psig, water hammer can result in very sharp and brief excursions above this value. One result could be relief valve popping; another could be pressure gauges jumping beyond the upper limit pin, and sticking there.

As you have mentioned earlier that you occasionally use boiler and mostly it is in standby position. steam gets condensed and upon start up of boiler it suffers Hammering. you should go for proper steam trapping devices (Strainers and Steam separators).

Secondly, If your S.V is set at 600 psi.It is not possible for water to come out of it as at this pressure there will be no water.

Thirdly, when you start a boiler from an offload condition to a full load condition. You need to do it gradually and if not Water carry over and priming will occur leading to entrance of water in steam connections.

Safety valves should be installed wherever the maximum allowable working pressure (MAWP) of a system or pressure-containing vessel is likely to be exceeded.