Wednesday, 25 November 2015

A Little Arithmetic

In one of my previous articles, I showed the boiler having a leg to stand on. I remarked that the 'leg' would be made from red band steel pipe when complete. However, when I considered this further, it would have meant a fairly long section of pipe on the end of which would be the blow-down valve itself.

I concluded that the torque required to operate the valve repeatedly could potentially loosen the pipe where it screwed into the boiler. In the worst case, it could damage the boiler's thread.

I decided that a heavy duty steel nipple would do the job well and be much stronger as well as being shorter. However, when I came to try such a nipple, it went up to the end of its tapered thread in the boiler's hole. Thus, I was not confident it could seal properly.

The Heritage Railway Association (HRA) have published a document on boiler plugs. They are very concerned that the male and female threads for boiler plugs should be compatible and not a mixture of seemingly well fitting threads. Whilst this blow down valve is clearly not a boiler plug, it does fit into a boiler plug hole with a tapered thread and I have ensured that the threads will be the correct fit.

Sentinel used 1.25" tapered BSP threads for their boiler plugs although they made the taper longer to allow for wear due to regular removal and replacement. Now for the arithmetic:
Plug + Nipple = Plug-nipple!
I asked Justin Goold to make me a nipple with the boiler plug thread at one whilst being quite normal at the other.

I have yet to check the fit but I'm sure there will not be a problem initially. I say initially because if wear does take place, the handle of the blow down valve will rotate with each tightening and not so easy to operate. Some care will be required.

Monday, 23 November 2015

Cylinder Oil Reaches Regulator

On a Sentinel locomotive such as 7109, Steam or Cylinder oil is injected into the superheated steam supply as a means of lubricating the engines' cylinders.

As the steam supply is at boiler pressure, the oil needs to be injected under pressure and that pressure is generated by a mechanical lubricator. I've described much of its configuration in an earlier article.

Part of the pipe leading from the Mechanical Lubricator to the regulator was missing from 7109 and I decided that it would be simplest to replace it and fill the gap using PTFE lined flexible high-pressure hosing with integral fittings.

Initial efforts failed to pump any oil into the new pipe section so I had a think and came up with a Heath Robinson construction to cure the problem. It actually follows from an idea described in the Delvac Mechanical Lubricator's manual (courtesy of the National Library of Australia). The intention is to use a lever to operate an individual pump as shown below.
It operates like this (Also on YouTube):

The end result is shown below:
Oil Dribbles from the bleed valve outlet
The braided flexible hose is shown fixed below the bleed, check and oil regulation valve assembly.

Sunday, 22 November 2015

Chuff Proofing (3)

In Chuff Proofing (2), I showed the 'completed' superheater steady plates for both inlets and outlets. I later realised that one of the screw fixings was loose and would need to be enlarged from 3/8" BSW to M12 and the hole re-tapped for a secure fit.
M12 screw highlighted on plates at the rear
(i.e. nearer the regulator)
Having enlarged the one I knew about, when checking, I found two more loose ones on the plates towards the cab front.
M12 screws highlighted on the plates at the front
(i.e. superheater inlet)
Hopefully these will all be secure in the long term and rattle proof. (I hate rattling noises).

Saturday, 21 November 2015

Vacuum Braking (15) Implementation (8)

Working Under Less Pressure than the boiler, the vacuum brake ejector requires 60 psi to work most efficiently. I began to describe this in an earlier article.

The missing item was a gauge to measure the pressure entering the pressure reducing valve.
Ejector Pressure Gauge Mounting
The gauge is clamped to the upward tube and marked mid-way between 40 and 80 psi.

Steam gauges are always fed by a tube with a loop or dip before the gauge. It collects condensation and prevents the steam entering the gauge and melting the soft-soldered delicate parts inside.

Wednesday, 30 September 2015

Working Under Pressure?

I've been fitting the boiler pressure gauge lately. It's red lined at 275psi and we have an original Sentinel type.

When I came to fit it, it seemed a good idea initially to adopt the alfresco approach as in the photo below.
Visitor-friendly alfresco pressure reading
One bright spark suggested that I ought to add wing mirrors so that the driver and fireman could also share the experience!

This leads me onto the point that the gauge does have to be visible by both driver and fireman so this mounting position is as good as it gets - so long as it's mounted on the inside!
Driver's eye view
OK, so some daftness has crept in here. In actual fact, it's more sensible than you might think. To drill and tap the M6 fixing holes through the cab front from the inside is not easy at all as the boiler is in the way. However, if one small hole is drilled through, the rest of the drilling and tapping can be done much more easily from the outside.
Fireman's eye view
Bearing in mind that there is a top cover to add height to the boiler, the gauge is still visible from both sides of the cab.
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