Is my safety valve functioning correctly?

[DannyTheElfman]

Hello again!

My apologies for starting another thread just a couple of days after my previous topic, I'm new to live steam so I have quite a few questions.

This one is regarding the safety valve and it's operation in my Accucraft Edrig. Basically, I was expecting for the boiler to reach 55-60psi and the safety valve to sort of "pop" open. But this doesn't really happen. Instead, At about 25psi the safety valve starts to release just a little of steam, at 30psi a little more steam leaks out, and at 35psi a little more, and so on and so forth until about 60psi. So instead of that single pop I was expecting, it's a gradual increase between 25 and 60psi. I could not identify a one single moment when the valve went from closed to open.

Is this correct operation? It does it's job, the pressure never goes over 60psi. But it seems like this wastes a lot of steam when it doesn't need to be?

Many thanks
Dan

 

[Rhos Helyg Loco Works]

No.

 

[DannyTheElfman]

Short and sweet, I like it! So what can I do to fix it? I've replaced the O-ring already (with these to be precise). It looked clean inside the barrel, no debris or anything. Maybe just tighten it down a little more?

 

[PhilP]

In the 12" to the foot world...
You would 'tap it gently' with a spanner..
It would then either seal, or blow-off enthusiastically!

If it was mine, I would flush the boiler out. Perhaps blow-through the safety valve with a foot-pump?
But not 'tighten' or mess with the adjustment.

I would then test again, and if no improvement, wander to a local group / model engineers, and get the hive-mind to give it a hard looking at.

But let's see what someone who knows what they are on about, says first..

PhilP.

 

[JimmyB]

I do not know this one specific, but basically there are two type of safety pressure valve, one like you mention that just pops off, drops the pressure to a percentage below the rated value, then seals again (pop valve). The other types starts to lift just before the safety pressure, becoming more open as the pressure rises, and then continuous to release pressure (seeps) until below the safety pressure.

 

[JimmyB]

As PhilP has said, do not try to adjust it, this needs to be carried by a competent pressure vessel engineer with the correct test equipment.

 

[Paul M]

I would seriously think about what Rhos and Philp say. Go to your nearest 16mm Association meet or your local model engineering society and get advice from there. You will get far more enjoyment out of your loco when running with other like minded folk. Where abouts are you in the UK?

 

[Rhos Helyg Loco Works]

Is it the internal O-ring you have replaced? If so the warnings about dismantling and adjusting might be a bit late! There is a tiny tiny O-ring inside and that will almost certainly be causing the problem. The ring goes hard with age and ceases to function correctly. Edrig is not a new model (introduced 2010 I think) so age may well be the causal factor. I used to have correct size replacement rings but they are long gone, so I cannot help you. One of the Accucraft repair agents (Repairs & Services | Accucraft UK Ltd) will be able to help, I am sure.

 

[tac foley]

Is it the internal O-ring you have replaced? If so the warnings about dismantling and adjusting might be a bit late! There is a tiny tiny O-ring inside and that will almost certainly be causing the problem. The ring goes hard with age and ceases to function correctly. Edrig is not a new model (introduced 2010 I think) so age may well be the causal factor. I used to have correct size replacement rings but they are long gone, so I cannot help you. One of the Accucraft repair agents (Repairs & Services | Accucraft UK Ltd) will be able to help, I am sure.

Dave Mees of Abbeybach Engineering Services Ltd is your man - one of the Accucraft service agents. He'll pre-test the replacement the replacement to the pressure as defined in the manual of the loco concerned.

Or you can buy a Wee-Bee safety valve from Simon Wentworth [anything Narrow Gauge] for about thirty English flarps. If you go the Mees route, tell him I sent you - we go back a long way.

 

[HobbitFertang]

In some ways a gradual opening of the valve is more re-assuring rather than wondering if it's ever going to blow off!

 

[PhilP]

That's why you have a pressure gauge, as well..

But our little-dragon's, will tend to go psssssssssst! If something untoward happens, and not BANG! as in the 12" to the foot, world.

PhilP.

 

[Paul M]

That's why you have a pressure gauge, as well..

But our little-dragon's, will tend to go psssssssssst! If something untoward happens, and not BANG! as in the 12" to the foot, world.

PhilP.

But it will still wreck your pride and joy.

 

[Fred2179G]

and then continuous to release pressure (seeps) until below the safety pressure.

My EBT #12 weeped continuously from the safety - very prototypical. It did not affect performance.

 

[JimmyB]

My EBT #12 weeped continuously from the safety - very prototypical. It did not affect performance.

As does my RH Fowler.

 

[Rhos Helyg Loco Works]

very prototypical. It did not affect performance.

I can tell you that (A) it is not very prototypical in full-size other than within a very few psi of a 150+ psi lifting point, and (B) yes, that "hole" in the boiler does affect performance. You are wasting gas and water, shortening the run.

 

[DannyTheElfman]

Hey everyone. Just a quick update. I heeded your warnings and took the engine to a a friend who works with compressors so I could figure out exactly what was going on. Several important discoveries were made.

First discovery: The big one. The pressure gauge is totally incorrect. At 55psi the gauge on the loco reads 45psi. The gauge appears to be pretty unreliable throughout the entire pressure range. Not good. This will be replaced.

Second discovery: Safety valve. As it turns out, this doesn't appear to be a problem at all. It starts to release a little trickle of air at 40psi and is fully open at 55psi. The "early release" problems I was describing earlier seem to have come from the faulty pressure gauge. The safety valve is functioning as intended, but I'm still going to send it away to have it looked at, just in case!

Last discovery: Barring the two previous issues, everything else seems to be in good condition. No leaks were found and the loco will hold pressure nicely. Pleased with that one!

I'll hold off steaming the engine until the two items above are rectified. Many thanks for your suggestions!

 

[PhilP]

Thanks for the update.
Always nice to know a problem has been solved, and what the answer was.

Enjoy!
PhilP.

 

[tac foley]

Has ANYBODY here, EVER witnessed a boiler in our area of model steam locomotion that actually 'burst'?

In over 45 years, I've never even heard of it happening.

 

[RDFMTS2]

Has ANYBODY here, EVER witnessed a boiler in our area of model steam locomotion that actually 'burst'?

In over 45 years, I've never even heard of it happening.

Well I have not heard of one, in my 60 years of playing with live steam engines, (30 years of live steam locos), they are usually over engineered to stand being handled I think. I don't usually run with meths now, so the main problem I see is gas valves not resealing after filling. I have seen several times a jet of flame above the gas valve, but as they have all been in a garden, a bucket of water soon cooled things down, followed by the owner taking the loco away from everyone / other locos, and letting the gas drift away safely. Only once was there any damage to the bodywork, which had a soft soldered side tank which was re soldered and repainted. Gas valves are relatively cheap so I change them every few years as I do run at quite a few indoor shows, and don't want to be the one who spoils the hobby's reputation for everyone, if a valve failure O ring should happen to me at the wrong time. I had an O ring failure once at an exhibition and gas came back out after filling but as I could see/hear it happening, so was still cold, I just covered the valve and went outside with it to let it empty itself, then put a new valve in. I think most of us will check the safety valve / pressure gauge regularly anyway, after all, the chances are we will be the one nearest the our loco if something did go amiss. Back to the fun of playing trains then. David.

 

[Rhos Helyg Loco Works]

Has ANYBODY here, EVER witnessed a boiler in our area of model steam locomotion that actually 'burst'?

In over 45 years, I've never even heard of it happening.

I witnessed one being tested to destruction with water. First, it visibly blew up like a balloon. Then, as the barrel distorted a joint failed around a bush. The leak from the joint was most unimpressive as the pressure was released. Had we been able to increase the pressure further it is most likely the gas flue would have collapsed.

50 years ago, I saw a home-built 4-6-4T part company with its boiler backhead, which accelerated away at a rate of knots. Poor construction techniques were to blame, not seen in a factory-built loco.

The picture shows a Roundhouse Linda boiler that got very hot when the loco was lit up with no water. An injection of cold water caused the damage. The loco still ran, no leaks!