By Julius de Waal

I heard from Bob Middleton about a design problem for a model steam ships capstan. The problem was how to achieve reverse rotation. His research online took him to the Markham Grange Steam Museum which has a website showing the restoration of a capstan. The engine has two cylinders with a common steam chest. There is just one eccentric driving the valve per cylinder.

The website quotes the following: " Reversing is achieved  by making both cylinder valves work as either inside or outside admission using suitable steam and exhaust passages in the base of the steam chest casting. The engine is reversed by a lever and cam in the top cover of the valve chest, which moves the control valve forward or back"

Bob explained: “I have not come across this before, and do not fully understand how this works. As we have pretty much a full covid lockdown at present in UK, with museums all shut down, I have been unable to get in touch with the museum staff who did the work on this capstan, so I am a bit stuck, and hope that you might be able to help me.”

So, I had a little think and had a fair idea how it worked.  I produced a drawing which is just an animated sketch of how it could work.

To understand the drawing a little more I have made some movie clips.

Please carefully note the position of the reversing handle.

After this exercise, I produced a designing a model two cylinder engine which employs the slide valves as reversers. See part two.

Click on drawings to download.

For personal use only.

Although drawings reproduce well on this website, they are even better as saved downloads.



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