I took my Saint for its boiler test and tried to fill the boiler using the hand pump but the clack valve was stuck. I tried to undo the valve cap and the valve sheared off. The valve had dezincified.

To access the valve, the whistle valve pipe, brake pipe, water gauge blowdown and hydrostatic lubricator and pipes all had to be removed (see photo).

I had designed the lubricator fittings to be easily removed so this wasn’t too difficult but I now needed to remove the broken part of the clack valve from the threaded boss in the back head. I couldn’t get 90 degree access from the back of the engine making it difficult to use easy outs, so on the advice of my friend Ken I tried using a Torx bit tapped into the broken end of the valve (see photo) and was able to unscrew it about 2 turns and then it seized up.

I tapped it in again and turned it half a turn but it seized again and I eventually carefully bored out the remains of the valve, which was like hard pink chalk, until all that was left was a ring of thread which I cut with a junior hacksaw blade and was able to split the thread ring and remove it.

The tapped hole in the back head needed to be cleaned up with a tap so I removed part of the drag beam to get a straight run into the hole and the hole was tapped out (see photo).

The clack valve that failed was purchased from one of our suppliers and had only lasted four years and one of those was during lockdown when the engine was only steamed once. The previous one lasted five years and showed no sign of dezincification when it was replaced and that was a commercial one also. It would appear that identical looking valves were made from different grades of brass.

Bristol Society member, Norman, advised I make the new valve from bronze and kindly offered me some if I needed it.

I found some bronze in my box of brass and made a new clack valve from bronze bar (see photo). The main body was made from phosphor bronze which turned easily but was a devil to drill, apparently tallow lubricates well but probably not a good idea if the parts need to be silver soldered. The last step was to silver solder the two parts together and this went well.

The final job was reassembly and touching in the paintwork that was damaged (see photo) and then booking another boiler test which was carried out successfully.