Titfield Thunderbolt in 5" gauge safety valves

[newington]

I am constructing one of these venerable old ladies and have all the articles and amendments from the model engineer magazines. I n one of the latter amendments (K.C. Miller 17 June 1963 page 717) there is mention of a modified safety valve "a semi pop type valve and disguise this in the boiler dome" Has any modeller tried this? or is there a drawing available that shows this modification. As the safety valves are such a prominent feature I would hate to spoil the the locos looks.

[jo479]

I'm making a 7 1/4" version by scaling up the 5" plans, Polly does the drawings for a 7 1/4" Safety valve designed by Gordon Smith, you could try scaling it down. worth a try it's good replica

[newington]

Thanks I will have a look.

[suctionhose]

I can't see why a Salter Valve cannot be made to work properly in miniature. I have them made, but not tested yet, for the 1880 traction engine I am building.



The reason the Salter Valve have a reputation is two fold:

1. they could be screwed down by the driver and were therefore associated with, though not always directly responsible for, boiler failures.
2. the seat configuration of these early devices did not utilise the "second seat" or "secondary area" to further lift the valve on opening.



It is a fundamental requirement of a relief valve that some element of the design provides an increased area / increased force to make it blow without exceeding the 10% pressure increase normally allowed by the Boiler Inspector. There are many ways to apply the principle. Here, mine will build up pressure in the "chamber" on account of the "restriction". The pressure will act on an increased area, causing the seat to open further until a new equilibrium with the spring is found.  

The Gordon Smith valves have well established themselves in UK so I recommend studying the arrangement. You may well be able to use the dimensions directly and reduce the spring by whatever the lever advantage requires.

My valve have an adjustable "blow down ring" just to make the final tuning easy to do without taking the valves back to the lathe while the engine is in steam.

BTW, Salter commenced business as Spring Maker around 1760 from memory. The Company still exists and was merged with an American precision equipment Co as recently as 2006.

en.wikipedia.org/wiki/Salter_Housewares

[steamer5]

Hi Ross,
Now that looks very nice!
How come we haven't seen more photos....or did I miss them??

I think Gordon did a design for a Salter safety valve, will have to check latter

Cheers Kerrin

[suctionhose]

Thanks Kerrin. Bits and pieces appear where it might be helpful but the main blog is on Traction Talk where the roadies mostly gather.
Ross

[steamer5]

Hi Newington,
Just checked the info I have on Gordon’s safety’s, it was a Ramsbottom valve I was thinking about. The list from Polly doesn’t list one for Lion.

I do have a part finished engine sitting on the shelf, I got it almost running on air back nearly 40 years ago, now the spiders think they own it!

Cheers Kerrin

[jo479]

If you let me have your email address I'll send you a photograh of mine.

[steamer5]

Hi Newington,

You might be interested in this....

youtu.be/gLgaH2fegM0

Happy viewing!

Cheers Kerrin