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Reversing a Piston Valve Engine

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As you have two passages into the cylinder that is what makes it double acting - steam pushes on one side of the piston and then the other.

It would be a single acting engine if you only had a connection at one end eg steam pushes the piston in a single direction and then the momentum of the flywheel exhausts the steam through the same single connection.

Right - it will still be double acting, the steam will just take an alternating path from the ends of the valve.

There were locomotives that were set up this way, they refered to them as either inside admission or outside admission piston valves, depending which way the steam/exhaust was hooked up. The original diagram you showed was inside admission, what you are proposing would be outside admission.

The more common way to reverse a double-acting engine is through a second set of eccentrics and a reverse linkage to select one or the other.

Thank you for your replies. I think that I need to do another set of drawings and try again. The sketch was done in Word. When I moved the valve in a second drawing using the same sizes, I found that both end inlet pipes were allowing steam in at the same time. I need to have a another look.

Thank you.


If you compare them, an outside admission piston valve is basically the same thing as a slide valve (D-valve) with steam on the outside and exhaust on the inside portion. The oly difference is that for the piston valve you have to route the steam to both ends seperately, and with the slide valve the steam can flow around the valve by itself.

Charles Lamont:
To make it run double acting, you need both the outer connections to be connected to steam.

Probably an easier way to make a reversible engine, without using a normal reversing gear, is to use a 'slip' eccentric. The eccentric driving the valve is free to rotate on the crankshaft. Beside the eccentric is a disk that is fixed to the crankshaft. The disc has an arc cut away, or a crescent shaped slot. The eccentic has a peg sticking out of the side that engages with the slot, so limiting the free rotation of the eccentric relative to the crank to 180.* The only thing is that it does not reverse automatically. To change direction you have to turn the flywheel half a turn in the desired direction to slip the eccentric round to its other stop.

* Not necessarily 180, but I don't think you are ready for that yet.   


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