Tuesday, 19 June 2012

Steam Brake Cylinder Completed (Again!)

In my previous article about the steam brake cylinder, I claimed the cylinder was complete and ready for installation. Honest, I thought it was but then I found that it really needed some tidying up and finishing off.

The previous paint used on the cylinder had been a type of red oxide but it is not specified to be able to stand up to the high temperatures encountered when pressurised steam is involved. I thus did some investigation and found a coating made by T&R Williamson Ltd who for many, many years have specialised in supporting the railway and other industries. They come well recommended and were very helpful on the phone.

New finish with the piston retaining ring in place
The chosen coating was a siliconised paint capable of withstanding 350DegC and able to be applied directly to metal. Its ability to iron out all brush marks and set with a silky smooth finish is amazing. I'll not mention the price!
Side view with condensate drain valve disassembled
I also mentioned previously the condensate drain valve which had had to be unblocked before it could perform its job again.
Valve ball and housing...
...with a view into the valve chamber
The appendage at the bottom of the cylinder body (it is normally mounted on a vertical surface) has a hole from the bottom of the cylinder into its chamber. A ball sits in the chamber and is held in slackly by a tapered screw-in plug with a small hole through it.
Screw-in plug with hole through it
When there is no pressure in the cylinder, the ball sits at the bottom of the chamber so that steam or air can pass by it and out through the hole in the screw-in plug. Excess condensation is blown out.

When steam or air is allowed into the cylinder under pressure, the ball is blown on to the tapered hole in the plug and prevents the steam or air from escaping. This maximises the force on the cylinder's piston and the loco's brake. (Also on YouTube).

video
Listen carefully to the video clip; when the piston is pushed fully out, the hissing through the condensate valve increases until the ball clicks over the hole. I hope this will work satisfactorily; it may need tuning with a different size of ball in practice.

When the pressure is released again the ball drops back into the chamber to open the hole again and allow condensate to drain.
 (Also on YouTube).
video
Again listen carefully; as the pressure falls, there is a pronounced Tick as the ball falls back into the chamber.

So that's how it works, I hear you say!

Post script 22nd June 2012: I tried a 0.75" ball instead of the 0.625" ball used in the videos. 0.75" is too large such that it blocks the outlet when the screw-in plug is tightened. I don't have a smaller ball to try so 0.625" it is. In this case, clearly, size matters!

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