How do I make a steam operated valve?

[nigel jones 5Participant @nigeljones5]

I have made 4 x steam operated cylinder valves and a lever which in one position supplies steam and in the other position vents the pressure line to air. Its essentially two discs rotating against each other with an airway machined into one.My problem is that it leaks from between the two halves, even when a lot of pressure is applied. I machined them with power cross feed, sharp tool, slow setting. So how do I stop it leaking? Some form of lapping operation perhaps?

[nigel jones 5Participant @nigeljones5]

[John ReeseParticipant @johnreese12848]

Fizzy,

Lapping is necessary. You can lap them individually on a flat lapping plate or lap one against the other. Even when lapped you are going to need enough pressure holding the plates together to resist internal pressure. It requires a very fine finish to make a reliable face to face seal.

John

[MWParticipant @mw27036]

Unless you can obtain a mirror finish on the surface i'd be doubtful if even that would seal it. You would be needing a perfect meet. As this is essentially a rotating joint it makes the situation so much harder.

Michael W

[nigel jones 5Participant @nigeljones5]

have any of you achieved this level of seal? It doesn't leak much as is but its only a machine finish. Any suggestions as to lapping compound or grade? Thanks

[John RuddParticipant @johnrudd16576]

Depends on the material the discs are made from….?? Mild steel, brass, titanium??

Start with coarse grade carborundum paste, finishing with jewellers rouge……somewhere in between these two ought to suffice maybe in stages starting with a less coarse to carbo, to something a little more aggressive than rouge

[Neil WyattModerator @neilwyatt]

Might be worth looking up LBSC's description of makling his 'disc in tube' regulator?

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Just a thought [blissfully unaware of the size you are working to] … Could the ceramic disc valve from a domestic water tap be adapted do the job ?

MichaelG.

[julian atkinsParticipant @julianatkins58923]

Hi Nigel,

Rotate with brasso (wet – dont let it dry out), and only in the movement that the valve operates. Check with micrometers blue.

I have made some fiddly bits over the years and the above procedure has always worked fine for me.

Cheers,

Julian

[Maurice Cox 1Participant @mauricecox1]

You could try relieving the area immediately around the pivot pin to allow the parts to bed together more easily, similar to my recent post to the chap who was making an oscillating steam engine.

Regards Maurice

[Simon CollierParticipant @simoncollier74340]

The next one I make will have concentric o-rings either side of the port slot/holes. The one I had made, just faced, worked well for ages but then started to leak and got worse. Attempts to face or lap it failed and I scrapped it.

Edited By Simon Collier 1 on 06/07/2016 00:07:18

[Anthony KendallParticipant @anthonykendall53479]

Posted by Neil Wyatt on 05/07/2016 20:30:56:Might be worth looking up LBSC's description of makling his 'disc in tube' regulator? Neil.

Good old LBSC was a great user of good old pumice powder, then available in different grades.

Unlikely you will find it in the local Wilko methinks.

Edit – loads of it on eBay – but probably stick to what Julian says?

Edited By Anthony Kendall on 06/07/2016 09:19:15

[Neil WyattModerator @neilwyatt]

Posted by Anthony Kendall on 06/07/2016 09:15:52:

Unlikely you will find it in the local Wilko methinks.

You're right, they are sold out of pumice stones, easy enough to make our own powder from one

http://www.wilko.com/accessories-and-tools/wilko-pumice-stone/invt/0125906

As Julian says Brasso is a good gentle polish its abrasive is sodium silicate, Astonish is more aggressive and probably more like pumice (Astonish contains quartz as well as sodium silicate, both commonly found in pumice), especially good for stainless steel (I have cleaned more than my fair share of burnt pans).

Neil

[Rik ShawParticipant @rikshaw]

I keep a tube of Solvol Autosol in the workshop for lapping and honing and wet it with Brasso where necessary.

Rik

[Bob YouldonParticipant @bobyouldon45599]

Hello Fizzy,

For lapping I'd suggest a product called Timesaver, take a look at http://www.newmantools.com/lapping/time.htm I've never had a problem using it, it does what it says on the tin! I also keep a tin of Ajax scouring powder, always useful in the workshop. It always helps if you use dissimilar materials for each face, e.g.. phosphor bronze or monel disc on a gunmetal face; yet another idea, a chap on another forum is insetting the disc faces with a PTFE insert,

Regards,

Bob Youldon

[Maurice Cox 1Participant @mauricecox1]

Hi Fizzy,

further to my post about relieving the area round the pivot; if you are lapping the faces on abrasive paper, make sure that the paper is held really flat on a genuinely flat surface; I use the ground base of my Fobco drill. Then, when you are doing the lapping, move the work in a figure of eight motion with even presure on it. After about six or eight stokes, turn the work through ninety degrees and repeat. Keep doing this and you should get a flat surface. If you just go back and forth, or in circles, this is similar to what mirror grinders do for telescopes. Not the shape that you want at all!

[nigel jones 5Participant @nigeljones5]

Ive tried anf failed with relieving and brasso, it was much improved but still leaked. So what alternatives are there? I see 3 way valves on ebay but im loathed to buy one. They are cnc machined at high speed and I simply cannot emulate that speed or accuracy. This is the last snag to my loco being complete! PTFE or derlin perhaps?

[nigel jones 5Participant @nigeljones5]

9o

[Michael GilliganParticipant @michaelgilligan61133]

Posted by fizzy on 12/07/2016 00:07:57:

9o

.

Does that ^^^ represent some noise made by your Avatar?

… Are you trying to communicate ?

[nigel jones 5Participant @nigeljones5]

my avatar has just explained that daddy is not her best friend! Doesnt help my valve though!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 05/07/2016 20:53:25:

Just a thought [blissfully unaware of the size you are working to] … Could the ceramic disc valve from a domestic water tap be adapted do the job ?

.

Ceramic disc was a serious suggestion.

Mention of domestic water tap was meant as a 'ferinstance'

MichaelG.

[julian atkinsParticipant @julianatkins58923]

PTFE discs would be a better and simpler solution with steam, if other metal to metal methods have not proved ok.

Cheers,

Julian

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