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Clack Valves
Posted by: Old timer (86.112.62.---)
Date: July 15, 2012 04:25PM

Hi all,
Having a slight problem with the feed clack balls on the water pump getting stuck between the seat and valve wall, we have fitted 1/2 inch stainless steel balls in there, shall we fit 5/8 balls or another size? There is no clack on the exhaust preheater although there is one on the economiser in the smoke hood. Any suggestions greatly appreciated. George

Re: Clack Valves
Posted by: les nelson (
Date: August 2, 2012 11:25AM

Hi George, clacks are sometimes a bit of an enigma as there are lots of things that can affect them, the size of ball is usually determined by the DIAMETER of the seating. ie on really small clacks the ball is mostly only 1/32" bigger than the seat, when you get to 1/2" balls I would say the best chance of success would be on a seat about 7/16" diameter a larger ball will not effect a cure on a "dodgy" clack, it is most likely the seat will need recutting, this is done with a flat bottom cutter to produce a sharp corner, the ball is then dropped in and given a sharp tap with a brass rod & a hammer to form a seat , ( very thin line of contact is all that is required), next problem is if there is room to fit a 5/8 ball in your clack I would suggest there is too much lift, this will affect the performance and when taken to extremes will stop the pump working at all ( Bin there etc), also too much diameteral (round the outside) clearance will give poor performance good luck with all Les

Re: Clack Valves
Posted by: Old timer (86.112.62.---)
Date: August 2, 2012 11:52AM

Hi Les,
Thanks for your advice, we've since had new phospher bronze seats fitted by a local model engineer (also retired engineer), we're also going to try and fit bronze balls as their not ment to hammer the seats like stainless ones. George

Re: Clack Valves
Posted by: (
Date: August 2, 2012 12:56PM

One approach is to use stainless balls until the bronze seat is well established, then switch to nylon or Delrin balls. Since the ball is much softer than the seat, you are controlling where the wear will occur. I'm still using the balls with stems that came with my pumps and haven't done this myself.

Dave Nergaard designed a nice O-ring-based check "ball" - []

I got some of these made and am keeping them in reserve.

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