Clack (Check) Valve.

Modelling the Kerr-Stuart Brazil Class 0-4-2ST locomotive in 16mm scale. - Keith Bucklitch

Clack (Check) Valve.


As we are going to fill the boiler via an ENOTS valve connector, we need a non-return valve in the system to prevent water/steam leaking from the boiler. Such a valve is colloquially known as a clack valve because of the sound they make (in the full size) as water is forced past the ball into the boiler. Valves are available commercially, but as we need to keep this as small as possible, we shall make our own.


1. Valve Body.



Start with a length of 6 mm (1/4") round brass bar in the lathe chuck. Face the end, centre drill and drill 1.5 mm for a depth of 12.5 mm. Open out to 3.2 diameter for a depth of 4 mm. Replace the drill bit with a 1/8" D-bit and cut the bottom of the hole to a depth of 4.5 mm. Tap 5/32" x 40 tpi for a depth of 3.5 mm. Part off the body at a distance of 12 mm. Replace in the chuck and turn the other end to a diameter of 3/16" for a length of 4.5 mm. Thread 3/16" x 40 tpi. Remove from the chuck. Make a centre pop, 3.2 mm from the top of the body, drill a 3 mm hole into the cavity. Run the tap into the body again to remove any burrs.


Chuck the 6.4 mm round bar again, face the end, centre and drill 1.5 mm for a distance of 7 mm. Turn the bar down to 3/16" diameter for a distance of 4 mm. (5/32). Thread 3/16" by 40 tpi. Part off the side piece at a distance of 6.4 mm. Make a threaded chuck by placing a piece of scrap bar in the lathe, and tapping 3/16" x 40 tpi. Screw in the side arm and turn the end for a distance of 1.25 mm until it is a firm push fit in the side hole of the valve body. Silver solder the two components together. Again, run a tap in the body to remove any burrs


2. Valve Cap



The valve cap can be made from round bar and a 3 mm square filed on the top for a spanner, or you can make it from a piece of 6.4 mm hex and leave it with a hexagon head. Start by chucking your piece of bar, facing the end, and turning down to 5/32" diameter for a distance of 3.5 mm. Thread this 5/32" by 40 tpi. Place a 3/32" diameter rustless ball in the valve body tap it gently onto the seating with a piece of brass bar and carefully measure the distance from the top of the ball to the lip of the valve. You require 0.75 mm (1/32") lift of the ball so deduct this amount from your depth measurement. Face the end of the cap until it is the length you require. Part off the cap according to whether you are using a square or a hexagon spanner head. Place a turn of PTFE tape around the thread and screw the cap tightly into the body. Shake the valve, you should hear the ball rattle inside. If not, recheck your depth and file a little off the cap. Blow down the valve. You should be able to blow easily in the inlet direction, and not at all in the outlet side. If your valve appears to leak, check the seating for any burrs. Try a new ball. If all else fails, make a new body for the valve. (You might reface the seating vary carefully by only a few thousandths of an inch.)



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If you have any questions, or comments or find any errors in these notes please contact me by email. Email Keith Bucklitch.

Copyright © 1998, Keith Bucklitch
Last Edited - November 1998