check valves

What type of clacks are people using, traditional ball type, o-ring seats or shuttle valve with o-ring face? I never seem to have much success making ball seats, despite all possible care, that totally seal. The same procedure produces hit and miss results. Bought ones are no better, some good, some not. I bought a set of oil and water check valves of the shuttle valve type, some time back, as yet unused, but I have heard only bad things about them. Are they any good?

Using a Viton ball instead of the usual stainless steel ball will give a good seal. The Viton ball should be "one size" larger than the steel ball.

Mick

If you use a brass bodied fitting to make a non return valve with a ball bearing and a spring, the magic trick is to seat the ball into the brass by giving it a sharp tap with a hammer and a flat ended punch. I have made non return valves for compressors using this method, and they don't leak!

Phil

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Years ago I used to make a high pressure ball valve, 2500psi, with a stainless ball in a brass fitting. We used to place a ball on the hole and strike it once, then build it with a new ball. Worked every time. That ball was around 5mm in diameter. On another assembly we used carbide seats and glass balls, 750 to 1500psi. These had to work out of the packet, you can't deform glass or carbide 😀😀.

Car tyre valves (Schrader valves) also work well and cost almost nothing. Grab a handful from your local tyre fitters as they cut them out and toss them in the bin when replacing tyres.

This sounds like a good idea. What is the opening pressure for a standard Schrader? Can the idea be successfully extended to safety valves? Given the application of these valves they must surely be manufactured to a very high standard.

Mick

Schrader valves are not a good idea on miniature loco boiler. on a hydraulic test they float.

cheers,

julian

Perhaps my sharp tap isn't sharp enough. I found and re-read the article on clacks by Gordon Smith in EIM Jan 2015. It is excellent but doesn't mention making the ball seat. His design does include a separate screwed in seat which allows the seat to be faced square with a fine finish. Thanks for the replies. I'll have a go at making one or two this week.

Dont forget you have to ream (or better still bore) the hole in the seat, as if it isn't truly round you will have the devil of a job getting a seal. Realistically it's too small to bore, so I use a D bit. Finish by very small facing cut from the inside to the outside, then you won't get any burrs. Instead of biffing it, if it is a screw in seat you can burnish it, stick a ball on the end of a bit of rod, spin the seat in the lathe and present the ball to it. You can inspect the seat with a loupe, if you see a shiny line all round it will seal, if not it won't.

I am aware of the need for a round hole. I can make a D bit easily but what about a slot or end mill? Hard to see how they could make a poor hole, say, drill 3.5 mm and use a 5/32 end mill?

Never tried it, but I suspect the end mill will act like a little boring bar and only cut on one tooth. Hole size will be dubiious. I've used toolmakers reamers in the past for similar jobs, easy to make, easy to sharpen, easy to use, just drill a hole a few thou undersize then poke the reamer through. All in the lathe of course, by hand might be iffy.

**LINK**

I use counterbores for forming flat seats with a hole in the middle. They are freely available for most sizes of imperial and metric bolts. I gave up on D bits years ago!

Roundness of the hole doesn't matter that much if the ball is struck to leave a complete circle of indentation. The hole is only an outlet and allows the ball to be positioned. Using a slot drill or end mill will not leave a flat face unless the cutter is well ground and the spindle is square to the part.

Does anyone have a drawing of a 'different' style of check valve say with the ball seating off to one side?

The tee type are ok but I want something different for my 4" Durham engine boiler side feeds.

Bri