Sunday, 1 May 2016

An Inconvenient Truth....

Progress in the last week hasn't been as straightforward as hoped.....! We decided to complete preparations for the forthcoming boiler hydraulic test by filling the boiler with water and pressurising it gently to check for leaks ahead of the formal inspection by the Boiler Inspector.

Filling the boiler was no problem after the two missing washout plugs were identified by a cascade of water from underneath the cab floor and refitted. It was very encouraging to watch the boiler responding to the increasing water level and showing no sign whatsoever of seeps or weeps from riveted joints or tubes. Cold water is very very pervasive and will find any weakness even at atmospheric pressure plus a low head. So it was good to get the boiler filled up to the top of the safety valve mounting flange and see everything 100% dry. The next step was to apply some pressure and hope that the regulator valve in the dome was holding tightly shut...and also that the blower valve was holding tightly...and that was when the problems started.

Once the dome filled above the blower take-off pipe we started to get water leaking from the blower ring in the smokebox on top of the blastpipe. Disappointing - but hopefully the regulator valve would be tight......and then water started running out of the steam chest. No tight shut-off at the regulator then! To every leak there is a solution. The blower valve can be removed in the cab and a blank fitted. The regulator valve can be accessed by removing the dome cover and replacing the valve with a blank flange. We started at the easy bit - the blower valve. The valve assembly (blower and steam sanding valve) was easily removed by taking out four 5/8" nuts and lifting the assembly clear and fitting a blank flange. Unfortunately this gave no improvement so the problem must be at the joint against the boiler itself (the blower valve is connected to the boiler by a swan neck casting). Removal of the swan neck proved to be anything but simple - all four mounting studs sheared during removal leaving us with four broken 5/8" studs to remove from the mounting pad on the boiler backhead. Fortunately at this point Colin Vaughan stepped in and used his engineering skill and strength to get the broken studs safely removed. Inspection of the joint faces between the swan neck and the mounting pad confirmed that this was where the leakage was occurring. The blower pad is riveted directly onto the firebox outer wrapper and is only fully accessible when all tubes and longitudinal stays are removed. As a result of the effort put into removing the broken studs two of the six rivets began to weep. This was the moment when our in-house riveting expert Calum Titley joined the fray and successfully caulked the rivets and stopped the leakage. New studs were fitted, the joint face cleaned up and a furmanite (high temperature jointing compound) repair applied and the swan neck bolted back in position ready for another attempt during w/c 1st May. And we still have the dome cover to remove.....!

The filling hose inserted into the boiler via the forward safety valve mounting 

Oops..! Who would have thought there were washout plugs down here....(the picture is taken from the pit looking up at the rear of the firebox outer wrapper. The clevis joint with the split cotter is part of the ashpan attachment.

Washout plug in place = no more leakage...!

A boiler full of water....

The swan neck casting for the blower & sanding valve. Looks like it dates from 1932..

The four broken studs after removing the swan neck...!

Arrival of the 5th Cavalry in the form of Colin Vaughan rescuing the situation..!

The broken studs safely removed thanks to Colin Vaughan

The blower mounting pad and the two leaking rivets. The large holes have internal copper pipes swaged into them to carry steam from the dome through the blower valve and forward to the blower ring on top of the blast pipe in the smokebox.

Calum Titley practising the art of rivet caulking (using a shaped chisel-like tool to gently upset the steel around the leaking  rivets) to achieve a water and steam tight seal

Everything tight now and new studs fitted

The swan neck bolted back in position and waiting for the furmanite repair to cure

Not 828 but a cab view of CR123 with the Mason valve for carriage warming pressure control just above the firebox door. CR828 has an identical valve offset to the right hand side of the cab.

Details of the Mason Valve - for some reason the one on CR828 is missing the main spring shown at Part 15 in the illustration. This explains why Nick Thomson and I had trouble working out how the valve operated when it was reassembled a couple of weeks back...

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