Searching for leak proof quarter turn water shut off valves

[GreensandsParticipant @greensands]

• Can anyone recommend a suitable design for quarter turn water shut-off valves as used in typically in 3.5 or 5ins gauge locomotives which are effectively leak proof in operation. Although this would be for model locomotives applications the scope could be widened to include stationary engine and model boat applications. All views and opinions welcomed.

[Nigel Graham 2Participant @nigelgraham2]

If sufficiently well-made and lapped-in, the conventional taper plug-cock is as good as any, and plenty of these appear among model locomotive designs. Designs for generic model engine fittings seem not to exist apart from a few samples in various text-books.

Cut the female taper using a D-bit type taper reamer made from silver-steel, on the same angular setting as turning the plugs. The better the reamer’s finish the better the mating surface inside the valve.

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The modern versions as used in domestic plumbing replaces the plug with a ball, held between two O-rings; one on the inlet, the other on the outlet sides. It is rotated by a tang working in a shallow slot, like a screwdriver and screw.

You can see how these are arranged by dissecting a scrap domestic-plumbing valve. Note that the diameter of the ball has to be significantly larger than the pipe bore for full flow. The slim-line domestic valves have quite small passages that must restrict the flow considerably. So a full-flow ball-valve may be a bit disproportionate but could be disguised as a globe-valve by machining the outside to a matching spherical form.

For the smaller model size, you could use a stainless-steel or phosphor-bronze ball, cross-drilled in the lathe with the ball gripped in a suitable collet resembling a pipe union.

Taper plug-cock bodies usually have a matching taper on the body. Make the body from two pieces of rod, silver-soldered together then machined.

[Alan CharlestonParticipant @alancharleston78882]

Hi Greensands,

I’d definitely go for a ball valve. My experience with taper – plug cocks in a chemical plant was not positive. The darned things were always either seizing up or leaked from the top or bottom. Not an ideal situation when the pipework was full of oooo nasty. I replaced them all with ball valves.

The ones that I’ve seen are sealed with teflon washers with the face machined to match the curvature of the ball rather than O rings.

Regards,

Alan C.

[GreensandsParticipant @greensands]

I have thought of using a ball valve application but I don’t think it would be a very easy thing to make up in the smaller gauges. The use I have in mind is for the engine to tender water connections on a 5ins gauge locomotive using 3/16 ins pipework. I have just discovered that Reeves sell a dedicated design of water valve for this type of use but it is not obvious from the image shown in their  on-line catalogue whether it is a ball valve construction. The cylindrical body shape would suggest not but it would be interesting to see a detailed drawing for the. design.

[noel shelleyParticipant @noelshelley55608]

If only as the basis of a task I often use 1/8″ gas threaded ball valves, a neat little chrome plated job usually male female thread. I would think these would be ideal on 5″ engines. There are bigger sizes ! Available at any good air power supplier Etc. Noel.

[Alan CharlestonParticipant @alancharleston78882]

Hi Greensands,

The Chinese web site which dares not speak its name on this site offers stainless steel ball valves with swagelok type fittings down to 1/8″ for reasonable cost.

Regards,

Alan C.

[Nigel Graham 2Participant @nigelgraham2]

Is that 1/8″ the bore or the connection? If the latter an 1/8″ BSP thread is approximately 3/8″ o.d. so the valve itself is fairly bulky.

I don’t know what modern motorcycles use but some older ones at least had quarter-turn valves for shutting off the petrol tank outlet. (Others had a slide-valve.) One of these may suit, and I have fitted one as the water-valve on my steam-wagon’s injector, with an extended control rod engaging its peg handle. I think it has 1/8″BSP connections.

For 3.5″ g and smaller 5″g locomotives LBSC once suggested using bicycle-pump hoses as the feed-bags between tender and engine. I don’t know the threads, and might want to ensure the fittings are not of mild-steel, but apparently he found the ones available to him, effective.

[duncan webster 1Participant @duncanwebster1]

The only application for water shut off valves on a loco are I guess the injector feed and the pump bypass. Does it matter if either of them leak a bit? Couple of chaps in our club deliberately let the injector feed drip as it keeps the injector cool, and if the bypass leaks a bit it just feeds a bit, not a bad thing within reason surely. Traditional injector water valves are just cross drilled cylinder in a sleeve, I doubt they seal perfectly

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