JB – do you have a drawing fot that there double clack – me likes the idea!!

Might have been one of those things that I just made out of my head but I'll have a look back. It's basically just a brass block for the clack housing with a bronze spigot soldered in the back to fit the clack bush and two more threaded spigots soldered in the bottom for the pipe connections.

John

No, just the one common drilling. IIRC think the back is drilled something like 1/4" diameter to take the threaded spigot that goes into the boiler and this drilling intersects both the ball chambers. I'm out at the club today but I'll try and knock up a quick drawing tonight when I get back. I've still got the loco at the moment so I can measure the clack for some dimensions.

John

Right, I've done a quick drawing with the major dimensions of the one I did but you can make it to suit: Hope you get the idea.

The body is a piece of rectangular brass bar, the two inlet bosses are also brass, in my case threaded 1/4 x 40. The spigot that screws into the boiler bush is bronze (I never use brass for bits that screw into the boiler) threaded to suit the bush. The balls are 3/16" dia. stainless or bronze. The holes for the ball seats are reamed and the bottom of the ball housing machined with a D bit or end mill to make sure it's flat. The caps are machine to allow the ball to lift 1/16" for injectors or less for pumps.

John

Edited By John Baguley on 21/09/2014 21:48:42

It seems to be the consensus that injector clacks need more ball lift than pump clacks and I have found this to be the case myself. The output from an injector is a continuous flow so once the ball lifts it stays lifted. The output from pumps is pulsing so the ball is continually opening and closing and tends to bounce around and may not seat properly between strokes if the lift is too great. This probably applies to axle pumps more than hand pumps where the pumping speed can be very high. I read an article in ME some years ago by a chap who had experimented with ball lift for hand pumps and found that in reality, very little lift is needed for a hand pump clack and the lift can be reduced considerably before causing any significant restriction in the flow. 1/32" lift for a hand pump is probably far more than actually needed.

John