1\2 express type safty valves

Hi just wondering if any one has a similar problem with Safety Valves like i am having on my 5" Black 5 i am using bought 1\2 express type boiler inspector set them to 90 psi but they don't close till it drops to 55 then have to start building steam again. I have cleaned out inside make sure no crud in them. all look good they are fairly new as Loco hardly been run since i built it but after endless problems not been running. I have tried to find out about fitting stronger safety valve springs i know they need to be stainless. I am inexperienced and still learning. I have a lot of Help from Julian Atkins but feel i am putting on him and feeling guilty he is going to do my two injectors that did not work bought ones again but he is so busy trying to sort this if i can but don't know how to get hold of correct springs. Can any one point me in the right direction please.

Ron

I dont think stronger springs will affect the closing pressure. That is usually more a factor of the larger diamter of the flange on the valve disc itself. As the valve lifts off the seat, the extra area is exposed to the steam pressure coming out the valve seat, which lifts the valve well clear of the seat with a "pop" as the steam pressure is now acting on a larger area. Likewise, the steam pressure on the larger area holds valve open until steam pressure drops considerably below the set pressure of the safety valve. If you want a narrower differential between the lift pressure and the closing pressure, you may have to use a different valve, or modify your existing valve by reducing the OD Of the valve disc, but check with your boiler inspector first as it may impair safe functioning of the safety valve.

A few years ago there was a series of articles by Gordon Smith about safety valve design, including design features for soft opening and low-differential closing. Not sure if these articles were in Model Engineer or Engineering in Miniature. Well worth finding and reading. JD

Well decided to buy two from B P steam had work done by him befor his blow of from 90 and only drop a couple psi.

Running at Southport on 24 and 25 so really would love a weekends running hopefully without too many problems.

fingers crossed

All the best with the running.

Fingers crossed be nice to really have a good run.

I have ran it before but so many problems with injectors axle pump if it could go wrong it did.

I think i need to buy a spare injector as a back up but so worried about buying another that does not work.

Ron