clack valves

[Nigel HydeParticipant @nigelhyde97004]

Hello all,

I need to make some new clack valves for a new loco.

Has anybody any drawings or advice on making clack valves with a shuttle and o rings rather than balls?

 

thanks Nigel

[Nigel HydeParticipant @nigelhyde97004]

clack/check valve drawings

[mgjParticipant @mgj]

Is there an advantage particularly?

 

For clacks to operate properly they need to be relatively friction free – some use plates and hair springs, or if you had room you could use what the motorbike world calls a reed valve .

 

I would have thought you might be making a rod for your own back there. Unless the thing is physically driven backwards and forwards you may find that friction slows the action down and it becomes a “sort of NRV” and not a proper NRV. You could use hydraulic pressure to dive it shut I suppose, but you’d have to be very careful to get areas of annuli and chambers just right.

 

Why not use a free floating shuttle and taper seat? that would reduce friction, but you still have the problem of getting the water past the shuttle- (annular groove or radial grooves), and you still have the problem of getting closing pressure onto the top of the shuttle. and keeping the shuttle vertical and effectively aligned – in our sizes. 

 

I haven’t thought about it in any great detail, but it seems a complex approach to a problem that has already been solved very simply?

Edited By meyrick griffith-jones on 23/01/2010 23:03:14

[mgjParticipant @mgj]

Oh I forgot- look inside some of the chainsaw carburettors and they use a shuttle type of NRV . Basically its a tapered rod operating into a tapered seat. The rod has 4 flats machined on it, which allows the fluid to pass. Those are forcibly closed by a diaphragm action, (some are positively opened by a diaphragm and closed by a hair spring, but it’s all the same thing). A little disc on the top of the rod would give you some area for the closing pressure to act on.

 

More complicated to make, and wouldn’t work any better than a ball of course, but its a route you could look at.

Edited By meyrick griffith-jones on 23/01/2010 23:32:42

[Nigel HydeParticipant @nigelhyde97004]

Hum yer

 

 i am after an easy option!

 

 then can i replace my balls in my clack valve with a nitron ones?

i am concerned about the sharp edge on the seating will this damge the ball?. am i worring over nothing?

 

thanks Nigel

 

[mgjParticipant @mgj]

Well I asked about sealing clacks on this forum – go back a bit and you’ll see it.Tells you how much I know about model clacks.

 

If you burnish the seat, the ball doesn’t seat on a sharp edge.  You need to talk to someone who really knows, but any NRV will fail in the end. All I can say, by using the methods given in the thread all my clacks seat and seal just fine. Thats the first half of the battle!!!

 

Being on a traction engine, if they do fail at least they are easy to get at!

 

Still, making them is dead easy.

 

Whether you are worrying about nothing I don’t know, but Confucius say stainless ball harder than bronze seat – bronze seat not damage ball. (but the ball might damage the seat, in which case I shall remake the seat – 10 minute job).

 

If that doesn’t work,  then we shall both be in the same boat.

Edited By meyrick griffith-jones on 24/01/2010 21:54:12

[CirclipParticipant @circlip]

1 ESSENTIAL tool Nigel, a “Punch” made from a piece of bar whose diameter is a sliding fit in the clack body. Centre one end to allow a ball to be accurately centred when in the body. On a FRESHLY faced seat, put the ball in the body, place the “Punch” in to centralise the ball and give ONE slight TAP (NOT Tubular Bells) on the punch end. Remove punch and ball, fit NEW ball and you should have a good seal, if not, RE-CUT the seat and repeat. Too many think that a crater is required for a seal.

 

  When re-cutting the seats you should only need to remove Thous (Single figures)

 

   Regards  Ian.

[Nigel HydeParticipant @nigelhyde97004]

Thanks everyone

I have now re seated my clack’s using Circlips method and it works well.

All i need now is more time to play trains!!! (story of my life !)

 

thanks again

cheers Nigel

[CirclipParticipant @circlip]

You should never need to burnish valve seats. Used to watch with some amusement people hanging onto valve stemswith a drill chuck and rotating at high revs to get four stroke valves to seat/seal, grinding paste all over and recessed valve heads, DOH!

 

  Regards  Ian.

[mgjParticipant @mgj]

Oh I don’t know. On the racing engines a touch of Brasso used to make them really seat without too much edge thinning. That’s burnishing/polishing. Valve grinding paste is lapping, but it has its uses – if used sparingly and correctly?

 

The solder a SS ball into a rod and spin in seat with a tiny dab of Brasso does very well in gunmetal seats. To a degree, the wider the seat the longer it will last. So there are merits either way.

 

The trick is alignment and quality of surface – as I discovered to my cost just recently.

[macmarchParticipant @macmarch]

Hi All,

Nigel, If you want to make ‘o-ring’ type claks/nrv then have a look at ME 10 December 2004.

[Nigel HydeParticipant @nigelhyde97004]

Thanks macmarch

when I am up the club tomorrow i will dig out that mag.

boiler test for a new tich boiler tomorrow I might take my wellies!!!

 

 thanks  to everybody who has posted a response on this subject

Nigel

[macmarchParticipant @macmarch]

should have added page 681

 

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