Steam Pump

[SignalFailure]

I'd like to make a steam-powered water pump and I've been studying Elmer's Vauxhall donkey pump but I think it's a little beyond my abilities/equipment at present, mostly because of the precision required in the valve area (a total travel of 2.5mm doesn't leave a lot of margin!)

It occured to me that I could re-arrange my last project to provide a 'direct drive' pump by putting the crank/valve rod on the opposite side of the cylinder to the piston rod/plunger something like this schematic...

Can anyone tell me if there is any inherent defect in such an idea before I waste time in a CAD program? Ta muchly!

 

[tel]

Nothing wrong with that scheme mate, been done plenty of times in model and full size - go for it.

 

[SignalFailure]

Cheers Tel... I'll think on the detail a bit more now

 

[tel]

Another scheme - available as castings.

Cylinder goes on the 'empty' end - the red bit in the middle is a scotch yoke connection. Must get and finish that one day!

 

[mklotz]

I guess I'm missing something. To my eye, what you've drawn is exactly the arrangment employed in Elmer's donkey pump with the slight difference that he puts the valve chest on the side opposite the flywheel.

Go for it. (After looking at your website, I don't think you'd have a problem with the donkey pump.)

I built the donkey and it works nicely. Rather than pumping water, I use mineral oil for demonstration purposes because it self-lubricates.

 

[kf2qd]

Don't need the flywheel. Let the piston rod bump the valve back and forth - does run away if it runs out of water...

Used them on lots of steam locomotives.

 

[SignalFailure]

Tel, is there an eccentric and that shaft to control the valve? Is that one of the Stuart pumps?

Marv, sorry I didn't make it quite clear, I wanted to eliminate two things from Elmer's design - the awkward top cylinder head/bearing and the slide valve mechanism. I thought I could rotate the crankshaft through 90 degrees and put the flywheel on the side of the engine rather than the front, extend the backplate (column) and put some standards at the top. That would give me room to use a simpler piston valve powered by a crank.

As a test I made the crankshaft as per Elmer's design but I've no way of accurately measuring the offset of the pin from the centre of the shaft once made (it should be 1.2mm - oh did I mention I'm converting it to metric too to match my equipment? ) If it's 0.1mm out that means a 10% change in valve travel which given the size of the valve/ports could be a killer.

Must admit that compact design that Tel posted suddenly looks appealing!

kf2qd: I was wondering about the flywheel but I guess it smooths things out when there's a variable load on the pump end??

Thanks for the input all.

 

[tel]

Tel, is there an eccentric and that shaft to control the valve? Is that one of the Stuart pumps?

Yes, there's a 'normal' eccentric and slide valve. And no, not a Stuart - it's actually an O.B.Bolton design from Ernie Winter.

The castings aren't really needed, Jessie Livingston, in beautiful downtown Tennessee, built a very credible one from barstock 2 or 3 years ago.

PM me if you want, erm, more info

 

[mklotz]

As a test I made the crankshaft as per Elmer's design but I've no way of accurately measuring the offset of the pin from the centre of the shaft once made (it should be 1.2mm - oh did I mention I'm converting it to metric too to match my equipment? Cheesy ) If it's 0.1mm out that means a 10% change in valve travel which given the size of the valve/ports could be a killer.

When I have to accurately offset a drive pin like this, I first turn the piece to size in the lathe. Then I mount it in a collet holder held vertically in the milling machine vise and use a DTI to center the part under the spindle. At that point you can dial/DRO in the required offset and drill the hole in the part for the pin. Your placement accuracy is then as good as your mill's accuracy.

 

[SignalFailure]

Thanks Marv... trouble is I don't yet have all that 'fancy' gear (collets, DTI... the good lady is still reeling from the purchase of the micro mill!).

I centre drilled the turned piece in the lathe, put it in the mill vice and used the finest point I could find to get it centred using a magnifier, then used the feedscrews to get the offset. By eye the final result looks about right although I'm pretty sure there's the tiniest of curves in the 1/16" pin, so the end may not be exactly in line with the hole anyway! It's all a learning curve...

 

[SignalFailure]

The layout of the Stuart pump looks as though it could be emulated using bar stock but the comments on this page are a bit of a concern...

http://www.stationroadsteam.co.uk/Stuart/steam pump.htm

 

[mklotz]

Thanks Marv... trouble is I don't yet have all that 'fancy' gear (collets, DTI... the good lady is still reeling from the purchase of the micro mill!).

I didn't mean to imply that any of that gear was essential to the task. Hold the part any way that's convenient. Accurate centering of a cylindrical part can be done with an edge finder (yes, that tool IS essential with a mill) and the Osborne maneuver. The "fancy" gear may make the job easier but there is always a work-around when you don't have it.

 

[tel]

The layout of the Stuart pump looks as though it could be emulated using bar stock but the comments on this page are a bit of a concern...

http://www.stationroadsteam.co.uk/Stuart/steam pump.htm

Yep, another doable one - somewhere here I do have at least part of John Bertinant's coverage of his build in the old SIMEC mag.

 

[tel]

... and for the uninitiated, here's some shots of Jesse's version of the Bolton P/8