Friday, 21 December 2012

Remote Control - 1927 Style

Starting from cold, Sentinel 7109, like any other steam loco, has many cold parts which cause the passing steam to condense until warmed-up. There are automatic drain cocks at top and bottom of each cylinder that open to release collected water. However, 7109 has pipework between the boiler and engines which also accumulate condensation.
Exhaust Condensate Valve
The picture above shows a white insulated pipe underneath the water tank that feeds the steam to the engines at the front from the boiler behind in the cab. Either side of it are two very dark coloured pipes which take the exhaust steam from each engine to the blast nozzles in the chimneys.

Running across the white pipe is another pipe which links the two exhaust pipes and includes a valve for releasing the condensate. If the condensate is left in the exhaust pipes, it has to go somewhere so every time there is a decent chuff from the chimneys, there is an accompanying decent hot shower for anyone nearby! So it's a good idea to keep the exhaust dry.

As the condensate valve is underneath the water tank, it's not very accessible for the driver in the cab. So a remote control mechanism is required.
Restored Condensate Valve
The above photo shows that the valve is spring-closed. Pulling on the handle on the right opens the valve against the spring compression.

The top photo shows a wire cable going off upwards to the right that is used to operate the valve. It has to pass around a couple of pulleys to a friction-loaded operating handle.
Pulley and handle mounts darkened
The handle is mounted on the cab's right hand side using two bolts. From the handle, the cable extends downwards to a pulley mounted below on the cab floor and then diagonally to another pulley just by the cross member (used for linking the sander operating levers from the right to left hand side).

I'm having to remake one of the pulley mounts as the original has been lost; the other and the operating handle have now been restored.
Pulley (not rocket science!)
The handle assembled with hardwood mounting block (1)
The handle assembled with hardwood mounting block (2)
I had to take this handle mechanism apart to find out how it worked and clean it up. Effectively, it is a sticky movement which, if set correctly, will hold the condensate valve open itself rather than the driver having to hold it.

In the above photo, there is a dark layer between the top of the base plate and the handle's cable drum. It is a friction pad made of either hardened leather or 1927-style plastic (which I guess would be Bakelite). There is a spring in the centre of the handle which holds the handle against the pad. For it to work effectively, the spring has to be tensioned correctly. I wonder if I've got it right? Time will tell.
Component parts
The friction can be set by tightening the bolt to compress the tapered spring.
DG Sentinel Waggon Parts Manual diagram
The above diagram is is from a DG (Double-Geared) waggon parts manual. Sentinel used standard parts all over the place.

It would be nice to be able to show the whole mechanism in place; however, it's not helpful to have a trip wire in the cab whilst there is still so much to do there! I'll include a final photo later.

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