Disc Steam Regulators - do they work?

[Tony K]

I am currently trying to get the disc regulator to work on my 3.5" loco. I have ground the moving part flat with Brasso etc on glass and am now grinding away with Brasso between the two disc surfaces. I am testing with compressed air at intervals with the operating mechanism disconnected and the loco on chocks. So far there is considerable improvement, but I am not sure whether I am trying to achieve the impossible - will it always leak a little? I just need to know that eventually this will probably work if I keep scrubbing away. Currently the loco does not run with the regulator in shut-off position (an improvement) but a small leak can be detected at the blastpipe. Is it likely to improve in steam? Someone out there must have experience of this. Thank you in advance. Tony.

[baggo]

Hi Tony,

Plenty of locos use the disc type regulator so they must be alright! In common with the slide valve type though, they will only seal if the valve and port face are perfectly flat.

Is it possible for you to easily remove the regulator block so that you can lap the port face seperately? This will probably give better results than trying to lap the two together, especially if the port face on the regulator block is badly scored or out of true. You might need to use something a bit more abrasive than Brasso such as a fine valve grinding paste. I used to grind telescope mirors and I've got loads of various grade Aloxite and Carborundum grits that I use for similar jobs. I just mix them with a bit of oil.

Also, is the operating mechanism allowing the valve disc to float slightly so that it can seat itself properly on the port face?

Incidently, are you using thick plate glass or just ordinary window glass? Plate glass has a much higher surface flatness than thin window glass which can be all shapes!

I note that you say there is a slight leak at the blastpipe. This possibly means that the valves in the cylinders are not sealing properly either and you are getting blowby past the valves.

John

[waggy]

Hi Tony,

As John says, lapping together can accentuate any surface deformities, you do need to flatten both faces before you attempt to bed them together. I used the finest wet and dry paper held flat on a piece of kitchen worktop, this stuff is extremely flat, provided it's not been allowed to get wet and distort. Wet the paper with washing up liquid slightly diluted and gently rub both parts in a circular motion, applying just enough pressure to stop any chatter. It worked for me!

Again, as John says, the disc must be allowed to float so the steam pressure forces the disc onto the port face. Have you got the disc rotating around a centre spigot? This is a must, if not you will get radial movement of the disc which won't help it to seal.

Daft question - I take it the disc is on the boiler pressure side of the regulator so it is held shut by the pressure?

Waggy.

[Tony K]

Thanks to you both for helping. Removing the regulator block is just a tad too adventurous for me at present, although I can see the advantages. Operating mechanism seems to allow the disc to float OK - but easing just in case. Have been using ordinary glass - rectifying that. Disc is on boiler pressure side and centre spigot now OK. Have both wet & dry and valve grinding paste - going ahead with that.
Will let you know how I get on, but will possibly be a week or so.
Once again, many thanks. Regards. Tony.

[Phil Sutton]

Hi Tony.Take very great care using grinding paste on brass,it tends to embed itself into the metal and you can't get rid off it,and end up doing more damage.
Good luck

Phil

[davidimurray]

Hopefully, no parts of the valve are made from Brass. Brass should NEVER be used when in contact with steam as it will disintegrate and go brittle.

I speak from experience on a full sized loco when a gauge glass blew, I grabbed the frame shut off handle, but on turning it the valve internals just sheared into two. Subsequent investigation showed that it had been made of brass!

Cheers

Dave

[Tony K]

Well, I said I would be back in about a week - it took a little longer. I think the discs are gun metal. I used a good chunk of plate glass as suggested. I was using Brasso for grinding purposes - finished up using two grinding compounds - fine valve grinding paste and consulted LBSC (his book, I could not contact him in heaven so perhaps he is not there!). He suggested pummice powder - you know the stuff always available in Tesco. Tracked some down on the net and gave it a go with circular motion on the glass and between the two surfaces with spigot removed and holes bunged to prevent grinding compound getting down to the cylinders. After two days and grinding my fingers down to stumps, things looked a lot nicer and my blood pressre was dropping too.

Something I had not noticed before was that the hole for the spigot is drilled through into the steam tube (by design). I therefore had to seal the threads of the spigot with Loctite 270. This gave difficulty at first because I got it a little proud and it held off the disc - negative progress, much stamping of feet, jumping around workshop and four letter words. Re-assembling each time to test with compressed air was a pain, but when you've been grinding for a while, anything else is more fun.

A little juggling and slight filing with the mechanism to prevent it holding the discs apart and success!

So, I suppose I can answer the question myself now - yes they do work. I am now as cunning as a fox who has got a degree in cunning at the University of Cunning as Blackadder would say. I still think the design is a bit crude but it works and I have not designed a better one, so I should not criticise. Meanwhile, does anyone want to buy some pummice powder?

Thanks to all, including the guys at Northampton SME. Regards, Tony.

[baggo]

Hi Tony,

Glad you've got it sorted at last. Patience and perseverance work wonders!

John