This is one for the model engineers on the forum (I think there are a few)...

I want to put better safety valves on my steam loco, as the ones I've got don't re-seat very well - they keep fizzing and bubbling once the pressure's gone down below the operating pressure.

Does anyone have a decent design for a 'pop' or 'semi-pop' safety valve? Or a pointer to one? It would have to fit a 1/2" x 26tpi mounting boss, and be an inch or more in height (but that dimension's not a major issue).

I've had a look through many model engineering mags, but the only interesting designs seem to use commercial springs (min. order £25 + VAT!).

cheers,
David

What is the blow off pressure

80 psi.

What sort of loco is it? It should be easy enough to make a pair of salter spring balance type with a nice machined and ground in cone that will seat well. may not suit all designs of loco!

Caber

It's this thing...



The design is called a "Sweet Pea", hence it's called "Lathyrus" (we've had that discussion elsewhere!). 5-inch gauge.

I know the type of safety you're talking about - I have considered it, and it would be in keeping with the general design. Not sure what the club's boiler inspector would think of them though...

cheers,
David

Safety valves often need a clout to reseat them when they lift --- but they shouldn't need lift in any other situation than when demonstrating to the surveyor that they lift. At SWP they shouldn't be any where near lifting.

Clouting the tops of the safety valves is NOT a good way to operate! Saying that, I'm having to gently tap the valves to stop them fizzing, which is a pain as they normally have 'chimneys' fitted on top.

That's why I want to make 'Ross pop' or 'semi-pop' valves - they do shut firmly, hence the name 'pop', which is the sound they make when they shut. The only disadvantage of the full 'pop' valves is the sudden and very load roar they make when they open, which invariably makes the user jump six foot in the air! The 'semi-pop' ones give a bit of a warning before they lift...

Just for a laugh, here's an old picture that shows my 'invisible man' impersonation!

He emerges out of the shadows to pass comment to an old mate..

Better we see steam than your face matey..

How the bloody hell are we?

Me? I'm bleedin' marvellous!

How's you?
(and I can understand the wish to avoid seeing my face... )

Ahhh you know..

Life ticks on.