Thursday, 28 March 2013

A Nice (Replacement) Pair!

Those of you who have been following the 'blog for a while will know that the restoration started out with a number of original bits missing. One by one, I've been acquiring or making replacements, sometimes authentic to the originals but not always. One example of the latter is the safety valves.

A typical Sentinel safety valve assembly is shown in the picture below which belongs to Isebrook at Quainton Road. It is very much an integrated assembly with the lower casting having the valve seats. Unless all the parts are present, this is not going to be an easy reconstruction - particularly as it needs to be accurately calibrated for the release pressure.
Isebrook's (6515) Safety Valves
Long ago, I concluded that this approach belonged in the 'too difficult pile' and that modern items should be used instead. (Later, if suitable authentic items become available, who knows what may happen but at least I know that the safety system will be reliable and accurately calibrated).

So these are the new devices: Bailey Birkett type 716SSL, size DN20 with the inlet below (3/4" BSP) and outlet to the side (1 1/4" BSP). One is set at 275 psi (18.97 bar) and the other at 280 psi (19.31 bar). The SSL part of the type indicates that the valve seats are made of stainless steel to handle the elevated boiling point found at 275 psi. Many thanks to South West Engineering Supplies of Chippenham for obtaining these.
Joyce's (7109) Brand New Safety Valves (1)
Each has the capacity to release the entire boiler steam output alone (4600 lbs/hours or 2087 kgs/hour).
Joyce's (7109) Brand New Safety Valves (2)
Now for the plumbing! Again, as the pressure is 275 psi, malleable iron pipe fittings are just able to withstand the working pressure but without a good enough safety margin. As a result, mild steel fittings and pipe work will be used.

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