Sunday, 29 September 2013

Maintenance Update

Weds 25th
Bruce decided to tackle the leaking steam heat valve.  This is an on/off valve that admits steam into the Mason's Valve.  The latter adjusts the steam pressure, taking it down from 225 psi to 40 psi max, to feed this steam into the coaching stock.  Because the on/off valve was leaking slightly, the pressure was gradually building up in the Mason's Valve.  It didn't matter when steam heating was in use.

So, Bruce removed the handle and plunger part and cleaned up the face of the plunger.

Then he examined the seat inside the valve body and discovered that it was this that was pitted.  To re-grind the face, the valve would have to come off.  It was a challenge to get a (large) spanner onto the retaining nut in a confined space near the cab roof!

Also, it was a double-threaded nut, and we didn't know for sure which way to turn it to undo it. Nevertheless, the two of us managed to persuade it to come off.  Bruce was then contemplating how best to hold the body and tidy up the seat.

Most of the time, I was fiddling around with boot scrapers.  Three immediate (staff) sales; plus: two to top up the trolley in the F&W and 4 to top up the trolley at Winchcombe!

Gil was floating about, too, though I'm not at all sure what he was up to!  I think he was cleaning up the thread on a bolt for the Siphon van.  He also arranged for Neil to fit a hose connector to the ash pan sprinkler system, so that we can hook up a hose and observe the spray pattern.  Crews do not use it, because water pours out of the ash pan when they do!  It might be a tad over enthusiastic in its spraying!  Fred plus Colin & Ann Bennett were all working on the Siphon.

Saturday 28th
Although I went to Todders, my state of unwellness caused me to to have to abandon it.  At that stage, Bruce had spoken with Carpo about the steam safety valves, and Carpo agreed to let Bruce do some lapping on them.  At best, this would show that no cutting was necessary; at worst it would highlight where cutting was needed.  Gilbert supplied the folowing:

Bruce got Rod to machine the seat of the steam heat valve to Carpo's satisfaction, The valve was then re-assembled and re-fitted to the locomotive.

He then got Carpo to let him have a look at the safety valve seats. He gave them a light clean-up and could not see any obvious fault which required them to be re-cut.  Carpo took a further look at them, and agreed that there was no obvious fault.

The concern had been that one of the valves feathers a lot more easily than the other one suggesting that it is not correctly seated. Because of this the valve plugs have been interchanged, and the problem has persisted.  (The valve plug is a loose piece that goes into the orifice of the valve and is held down by the spring and the spindle against the fixed seat)

Since the seats were considered satisfactory the valve plugs were scrutinised carefully and compared against the spare units. It was found that one of the existing plugs had been machined eccentric. This was seen by examination of the top of the plug where the land on the top surface appeared uneven at opposite sides of the plug.

Further scrutiny revealed that the centre bore which locates the bottom of the valve spindle was off-centre by approx. 1/16". The plug and spindle were set up in a lathe and the eccentricity was confirmed. The four guide vanes on the underside showed rub marks on two but not on the others, indicating that the plug was not lifting vertically. The conclusion was that the machining error was causing the plug to tilt when it tried to lift.

After discussions with Carpo, Bruce made arrangements with Rod to re-drill the centre in the top of the plug in its correct alignment.

On completion of this work it should be possible to re-assemble the safety valves.


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