Gordon Smith safety valve spring

Hi, I have just made two PSV2A safety valves to the Gordon Smith drawings and used the springs supplied by Polly ME. However they won't blow off even at 100psi and with the adjusters wound out. I have checked the spring spec on the Lee springs website and it is correct. Can anyone please tell me if they have experience with these valves and what I can adjust. I want 80psi.

I have heard that a couple of his designs are suspect, sounds like yours is one of them. Perhaps shorten the springs or if job allows machine the seat a bit deeper?

The pressure at which a valve opens depends on the area open to the steam, and the compressed load on the spring. The smaller the area (size of hole) and the stronger the force from the spring, the higher the blow-off pressure.

So, if you need to lower the operating pressure, you need a bigger hole or a lower spring force. The easier to do and certainly the easier to change back again is the spring. So you need a standard spring which is compressed less, or a weaker spring (not a shorter one*). This might mean a spring with thinner wire, or a larger diameter, or any combination of these.

* Shortening an existing spring will mean that the 'rate' of the spring increases - as well as the load at the original length going down. The rate determines how much extra load is added for each mm of compression - a high rate means a stiff spring and a low rate is a floppy one. Too stiff a spring on a safety valve might mean a valve which opens at the set pressure but does not open far enough to keep up with the production of steam (as its new more compressed length requires a much higher pressure to open further).

I hope this helps - they can be complicated things, springs can.

Regards, Tim

Thank you. But how can I get a spring the same dimensions but thinner wire? The only source of thin wire I can think of is steel guitar strings but they aren't stainless.

I use Entex Springs - **LINK**

There is sping calculator on the site and tables which give information on spring rate, wire gauge, lenght etc. I was given alecture by a mate many years ago who workd for spring manufacturer. H explained the principles, but they were beyond me and I have forgotten most of it.

Entex have never failed me and they will supply small numbers of springs.Prices are not prohibitive. No connection except as a happy customer.

Jerry

I'd contact Polly first, if there is a design problem they will be aware of it.

A good source of SS wire is people who make/fix false teeth. Try yellow pages

It is fairly easy to buy SS spring wire in a range of gauges - but you have to order a coil - ie enough to make 1000 springs and some to spare. If you cannot solve your problem at Entex come back to me and I may be able to help with a few inches or even a made-up spring. I will need to know the wire diameter, the turns diameter, the free length and fitted length, and the number of turns of your existing spring.

And what you want is not just Stainless wire, it needs to be 'hard drawn' or it won't be springy enough.

PS it is quite likely that you can get the right sort of wire from those who deal in radio controlled models, drones and such like.

Cheers, Tim

Hi Thanks everyone. Polly have supplied the correct spring to the design so I guess they have done all they can. I think the design is faulty and needs a weaker spring. I have looked online for stainless steel spring wire but haven't found any. I have got them working because I bought a 12 inch length of 5/32 spring from Polly and have made springs from it that are only 8mm long instead of the 11.1 mm specified. They now blow off at 80 psi but I don't think the pop action is very good.

Firstly let me start by saying the Gordon's range of safety valves were designed to over come the accumulation problems that most of the other designs didn't do. Also to stop the boiler emptying on the first lift, like some of the other designs did. They were also designed to work at 100psi. At other pressures, they needed some very small changes. My Jinty runs at 90psi and he very kindly helped me with the smallest of changes. I remade the ball shrouds .005 bigger in diameter. Also when I first made them the finish on the stems wasn't good enough, mainly because I had made them in stainless and not brass, and he very kindly took them home and sorted them out for me, including a computer listing of all the actions of both valves. Another reason they were designed was to get away from 'chopping' a length of spring of a longer length. He insisted on using the right spring with close coiled ends. I know for a fact that all his designs were tested on an electrically powered boiler at 3.4kw and 5.7kw, so if the valve could cater for the higher output, you could be pretty certain of it working on the your boiler. None of his designs were put on the market before they worked properly I do feel it wrong when someone says that some of his designs did not work, when I know the testing procedures that he went through. I think any problems could be do to a manufacturing error

Edited By Neil Wyatt on 03/04/2018 16:06:03

In support of Keith's comments and Mr Smith's work, I have built several safety valves of different sizes to Gordon's published designs and they all work exactly as expected, for me. As is mentioned, care in finish and on key dimensions for these and other safety valves is important.

Edited By Neil Wyatt on 03/04/2018 16:06:33

Hi All,

I can say without a shadow of doubt there is an error in the drawings for Gordon Smith's 'squat valve' PSV#2E from Polly. I had to go back to Gordon's original EIM articles to work out what the error was as the valve would not close till pressure dropped to 50 psi, working pressure being 90 psi. The answer was in Gordon's original articles and taking 10 thou off the bottom of the shroud resulted in perfect performance.

I have not seen the drawing that John has worked to, but in the light of the above the drawing I was making them to had an error.

The springs supplied by Polly were spot on and excellent in my case.

The parts do need to be made to a very high degree of accuracy, especially the body internal bore around the shroud retaining the ball, and the shroud itself.

Cheers,

Julian

Has anyone told Polly? it wouldn't be much of a job to put the drawing right. I've made 4 and they all worked spot on, but not the compact size.

Hi Julian, The valves I have made are the PSV2A, which have different springs to the PSV2E. I made the shroud to the max dimension and checked it with a micrometer. These blow off at 115 psi, not 100. I want 80 psi but none of his valves go down as far as that. I need the 5/32 bore size but don't want high valves. Any help would be much appreciated, Thank you. I've told Polly over the phone.

I have just heard the sad news that Gordon Smith passed away yesterday.

I had the good fortune to meet him at the Burton Club. He was a nice chap and happy to help people with queries about his designs.

I understand that last November, despite ailing health, he gave a talk on his safety valve designs to the club.

Neil

Edited By Neil Wyatt on 04/04/2018 09:32:14

Thank you Neill, I've done that.

Hello John, I'm afraid I had some sad news just now, so I have edited my post.

Neil

Gordon Smith passed away? So sad to hear of this. I have two safety valves made to his drawings. (They work well)

David