Safety Valve Springs

[timb]

All,

I have searched for safaty valve springs on this site and there is a lot of information regarding where to buy etc but very little regarding making them.

Is it the opinion that these should be bought or can I make them myself?

If I can make them then the drawing suggests a 26g spring but nothing else regarding number of turns length diameter etc.

Although I can probably work out the length and diameter, surely the critical factor is its compression value or is there something I am missing?

I would like to make the springs (I successfully made all the other springs for axle boxes and clack valves etc) is there an equation to use to work out the force required ot open a valve at a set pressure?

I have used stainless piano wire for springs and the occasional bronze wire for valves is this the right material for safety valves?  LBSC suggests tinned steel wire, whatever that is callesd these days!

Any help gratefully accepted (any sarky comments ignored)!

Tim

[stevep]

Tim,

The spring in the safety valve is a very important item, and to get correct operation (i.e. release at the correct pressure, keep the pressure within 10% with a full fire, and then to close again just under the nominal pressure) requires a lot of careful design.

Buying commercial springs ensures that the springs have the correct rate. Most people use the designs by Gordon Smith (obtainable from Polly Models) and these specify the exact spring to use.

[dfh]

Aug 22, 2020 14:53:43 GMT timb said:

All,

I have searched for safaty valve springs on this site and there is a lot of information regarding where to buy etc but very little regarding making them.

Is it the opinion that these should be bought or can I make them myself?

If I can make them then the drawing suggests a 26g spring but nothing else regarding number of turns length diameter etc.

Although I can probably work out the length and diameter, surely the critical factor is its compression value or is there something I am missing?

I would like to make the springs (I successfully made all the other springs for axle boxes and clack valves etc) is there an equation to use to work out the force required ot open a valve at a set pressure?

I have used stainless piano wire for springs and the occasional bronze wire for valves is this the right material for safety valves?  LBSC suggests tinned steel wire, whatever that is callesd these days!

Any help gratefully accepted (any sarky comments ignored)!

Tim

If you look at the attached web page kindly put on the net by Sutton Coldfield MES you will possibly find a valve to match want you want. It will give you the Lee Spring Co spring number, you can then search Lee Springs and it will give the dimensions and properties of the spring, balls and springs are also available from Polly Eng.
www.scmes.co.uk/images/Technical%20Information/SafetyValves/Safety%20Valves%20Master.htm
David
sorry about double posting

[uuu]

This book by Tubal Cain probably has everything you need and more. RDG website

Wilf

[suctionhose]

Actually, you can wind them yourself easily enough from stainless wire. You'll need to see that they hold the pressure with about 50% deflection and don't become coil bound.

Aim for small dia springs which can be of small wire dia and still carry the required load. Just copy something from a catalogue for no of coils, wire gauge and length.

The final tuning of the valve's secondary seat and lift characteristics will accommodate variances in the actual spring you make.

If none of the above makes sense then stick to the proven designs. I like mucking about with SV's hence the assurance that a particular valve can be matched to a range of springs, though once established, the spring and valve are partnered permanently.

[timb]

Thanks all for your help and suggestions, I think I will give it a go and see what happens. I have a mind to rig up a test jig and try different springs and go from there. Worst case I will buy one but there is an opportunity to learn methinks!

Tim

[johnhale]

You may want to look out Jim Ewins Safety Valve data, this linked the grate area to the size of bore, seat and spring. The article was in Engineering in Miniature around 1988 about and experimental 9F. Here's a link to some other information he published.

www.maidstonemes.co.uk/media//DIR_17401/spring88.pdf

[Jim]

Aug 23, 2020 2:13:58 GMT suctionhose said:

Actually, you can wind them yourself easily enough from stainless wire. You'll need to see that they hold the pressure with about 50% deflection and don't become coil bound.

Aim for small dia springs which can be of small wire dia and still carry the required load. Just copy something from a catalogue for no of coils, wire gauge and length.

The final tuning of the valve's secondary seat and lift characteristics will accommodate variances in the actual spring you make.

If none of the above makes sense then stick to the proven designs. I like mucking about with SV's hence the assurance that a particular valve can be matched to a range of springs, though once established, the spring and valve are partnered permanently.

I wound my own springs for the Britannia's safety valves as Ross describes above.

I used the lathe to hold  a steel rod of suitable diameter as the former, the stainless wire was clamped between two blocks of wood in the tool post so the wire could be pulled through under tension. To get the required turns per inch I used the thread cutting settings. I pulled the lathe chuck round in reverse by hand and watched the spring being formed at the correct 'TPI' along the rod. I added some extra turns to allow for trimming the springs.

The system works well and I had my own custom made springs as described by Gordon Smith.

Jim

[suctionhose]

Been talking safety valves with a member of another forum... Thought this picture might be of interest. Shows three equivalent springs. All can function successfully in the valve shown albeit a spacer is needed. In fact, the largest spring was in the valve shown. I made new valves for the same boiler with no change to orifice dia's and used the smallest spring.



Basically, if the spring holds the pressure down with about 50% deflection then a seat and second step can be contrived to pop open and closed satisfactorily.

[timb]

Aug 22, 2020 16:32:42 GMT uuu said:

This book by Tubal Cain probably has everything you need and more. RDG website

Wilf

Book arrived yesterday Wilf, more bedtime reading.

Thanks for the tip!

Tim

[timb]

I thought the number of coils and the diameter all contributed!
I will read the book!!

Informative photo Ross, thanks.

Tim

[johnhale]

Eventually managed to dig this out and create a account for hosting images, hope this is of some use to someone

<img src="" alt="" style="max-width:100%;">

[johnhale]

Sorry for the massive image still trying to figure out how to add images from IBB hosting site

[92220]

Hi John.

I don't know that hosting site, but I notice in the host details, there is a 100%. Perhaps somewhere in the site, when you get the picture code to share it, there might be some way to reduce this percentage to say 50%.

Bob.

[timb]

Thanks for the info John, regardless of size!

Tim