Fusable plug for 5″ gauge

Fusable plug for 5″ gauge

This topic has 9 replies, 6 voices, and was last updated 15 April 2015 at 13:26 by andrew winks.

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15 April 2015 at 07:21 #186440
andrew winks
Participant
@andrewwinks64215
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.
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15 April 2015 at 07:21 #1392
andrew winks
Participant
@andrewwinks64215
15 April 2015 at 10:21 #186451
Dave Bond 1
Participant
@davebond1
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.
15 April 2015 at 10:30 #186453
Steambuff
Participant
@steambuff
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
15 April 2015 at 11:34 #186460
Neil Wyatt
Moderator
@neilwyatt
I think the head of the rivet inside the firebox is stop stop the fire eroding away the plug.
15 April 2015 at 12:39 #186468
andrew winks
Participant
@andrewwinks64215
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.
15 April 2015 at 12:58 #186471
JasonB
Moderator
@jasonb
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
15 April 2015 at 13:15 #186477
Paul Lousick
Participant
@paullousick59116
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
15 April 2015 at 13:24 #186478
andrew winks
Participant
@andrewwinks64215
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.
15 April 2015 at 13:26 #186479
andrew winks
Participant
@andrewwinks64215
My comment earlier about comsol is certainly incorrect, melting temp too high
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