Saturday, 7 March 2015

Boiler Plugs & Clamps

Friday 6th March was a day to complete a couple of small tasks. Some time ago, I'd been concerned about a rather inadequate looking boiler plug as in the photo below.
Boiler Plug?
The 'plug' blocked a hole in the steam space on the right near the safety valve mounting. This little item has been with the boiler since it arrived and was used during the initial hydraulic test of the boiler.

What concerned me was that the main part of the 'plug' consisted of a malleable iron socket. As a material, malleable iron is definitely not recommended for use with steam at 275psi!

The Heritage Railway Association (HRA) has produced a report on boiler washout plugs and go to great length to ensure that the correct tapered threads are used on the plug to match that of the tapered hole. Here, Sentinel have not used a tapered thread at all; it is a parallel thread (1/2" BSPP)!

After much searching, I found a source of suitable parallel plugs made from 316 stainless steel. Peter Hawkins, our boiler inspector, is happy with this as a strong enough material for the plug although he pointed out that it may be difficult to remove in future. Stainless steel tends to snag against stainless steel; however, the boiler itself is not stainless and so I have decided to take the risk. (I hope I'm right as this is a useful hole for putting water into the boiler!).

The plug is now tightened to 50Nm torque on to an annealed copper washer with Steamseal in all the right places to prevent any leaks.
Boiler Plugged!
In fact, two holes have been plugged in this manner. The other is also in the steam space but on the left hand side and was originally used to supply a steam lance (long before the invention of pressure washers for cleaning purposes).

The new and the old:
And the new one doesn't rip your clothes as you squeeze past!
The second task was to fit six [ shaped clamps to hold the boiler top plate in place. These I had made after my welding course about three years ago.
One of the six
(with lashings of graphite grease!)
This week I also spent much time (and money) obtaining the pipework and fittings to construct the vacuum braking system. The other little task on this date was transporting the steel vacuum pipe to Midsomer Norton station as below.
Have Pipe will Travel!
There's a lot of vacuum fitting ahead in the next few weeks!

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