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Uniflow Engine

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PaulR:
Actually not sure whether these are call uniflow or unaflow engines but...

I bought Stan Bray's book when it came out in 2005 and tried to make his uber-simple 'Clapper' engine but it completely failed to run. I don't have the engine or the book any more but I thought it was time to revisit the idea. I know there's a thread on here about a large scale and moire elaborate version and that there's a double acting version in Elmer's repertoire but I want to keep it as simple as possible.

From what I remember the basic principle is like the attached, where a pin on the piston lifts a ball to admit air which is exhausted when the piston passes holes in the sides of the cylinder. I'm not sure if the piston should go further than the exhaust ports, allowing more time for the air to be squeezed out on the upstroke or whether the air in the cylinder will already be at atmospheric pressure by the time the piston has just passed the ports?

If I thread the 'retainer' above the ball it could be adjusted to see the effect on performance. Also, it seems like the vertical orientation shown would naturally work better as far as the valve is concerned rather than the engine being horizontal.

Any advice please?

Jasonb:
The piston on the Husky that I made drops about 1mm below the holes (18mm bore) These engines always run a bit differently on air as you are compressing any that is left in the cylinder as the piston goes up rather than any remaining steam condensing.

In this case I don't think adjustable bal lift will do much as the flow of air will be pushing the ball down onto the actuator. unlike a non return valve where there is only the liquid pushing it off the seat. But as you need to get the ball in somehow may as well thread it and have a bit of adjustment. Probably better to make the actuating rod adjustable then you can alter when air starts to enter.

AVTUR:
I am not sure whether I can really help.

Back in the 1960s the Science Museum, London, published a booklet, price 20p, titled "The Steam Engine". In it there is a short piece on the Uniflow engine with a diagram and photograph of a model. The first attempt at making such an engine was in 1827. Its steam working pressure was 1400psi! By 1908 the problems with such an engine had been over come and engines were manufactured for about twenty years.

I would like to put the image of the two pages in this reply but copyright applies. If anyone wants to hunt down a copy it was published by Her Majesty's Stationery Office in 1965 with a third impression in 1972.

AVTUR

Jasonb:
The model boating fraternity sorted out uniflows, popular engine type when combined with a flash steam boiler.

PaulR:

--- Quote from: Jasonb on September 20, 2025, 10:08:12 AM ---The piston on the Husky that I made drops about 1mm below the holes (18mm bore) These engines always run a bit differently on air as you are compressing any that is left in the cylinder as the piston goes up rather than any remaining steam condensing.

In this case I don't think adjustable bal lift will do much as the flow of air will be pushing the ball down onto the actuator. unlike a non return valve where there is only the liquid pushing it off the seat. But as you need to get the ball in somehow may as well thread it and have a bit of adjustment. Probably better to make the actuating rod adjustable then you can alter when air starts to enter.

--- End quote ---
Thanks for this. I'm thinking of using a piece of hex for the cylinder with supporting columns attached to one pair of sides and decent sized exhaust ports on the other four.

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