I have been building my 7 1/4 Terrier Boiler as mentioned in an earlier post. I am following the drawings produced by Don young in 1990.

All has gone reasonably well until the first Hydraulic test. We took the pressure up to 100psi, water issues were minimal primarily a very minor leak on the foundation ring and some seeps on four firebox stays. I felt quite happy with this until a detailed inspection ( empty boiler) revealed a bellow on the front firebox tubeplate. This was positioned below the bottom row of boiler tubes and the top row of the throatplate stays.

There is a flat area of 1 3/4" * 2 3/4 " that is unsuported by stays. Every where else in the firebox stays are martixed at 3/4".

We reheated and gently pressed the plate back to where it should be. Fortunately the top bend on my outer throatplate where it meets the boiler outer was a sharp radius and I have managed to get 3 stays threaded into the centre of the unsuported area which continues the 3/4 " matrix stay layout over the flat area the front tubeplate. The new stays are in line with the stays on the sideplates.

Pressure test to 150 psi has been OK. I still have to go to 180 psi when Ive sorted the Foundation ring but do not envisage a problem.

It may be that on the drawing a row of stays has been missed.

Anyone building a 7 1/4 " Terrier Boiler may want to look at this issue closely.

Ianmac

Yes,

I appreciate where you are coming from. The boiler had been away from heat for a few days before the test

From my point of view with a Boiler I prefer to opt on the side of safety. Club Boiler inspector is of the same opinion