Fusable plug for 5" gauge

Hi all, anyone with experience making a fusable plug for a copper boiler firebox?

I have a 3/8 ME bush in place in the crown. The plug I believe is drilled and filled with low(ish) temp soft solder but I've also heard of some with a copper rivet sweated in. Advice greatly appreciated.

The copper rivet is I believe designed to blow out leaving a large hole. Just filling with soft solder there is a small risk that the plug re-seals as it cools during pressure release as not all solder would be ejected from the plug.

I don't think the plug would reseal if you filled it with Solder or (usually) White-Metal as it would drop into the fire as it melts and the pressure would tend to blow it into the fire as well.

Dave

I think the head of the rivet inside the firebox is stop stop the fire eroding away the plug.

I agree Dave, once the solder softened and gave way, steam blow would continue until the boiler pressure dropped to atmosphere. Yes, Neil, I would agree the rivet would protect the caulk. My thoughts would be a 1/8" copper rivet sweated in a very sloppy clearance fit in the corresponding hole drilled in the gunmetal plug. Solder, perhaps comsol, gets the highest temp.

All the posts I have read in the past on traction engine forums say solder is a NO NO. The Aussie code is tin for presures upto 150psi and pure lead over 150psi.

J

Extract from Australian model code for boilers. (max. pressure for models is 100 psi)

Tin melts at 232 °C (450 °F) ,    Lead melts at 327.5 °C (621.5 °F)

Paul.

Edited By Paul Lousick on 15/04/2015 13:19:45

Thanks Paul, I do have a copy of the Au code but wondered where tin could actually be sourced. Thats why i was also thinking solder with high tin content.

My comment earlier about comsol is certainly incorrect, melting temp too high