Poor mans one-squeeze miniature pump

While the main project is still suffering from some alignment problems I thought I'd build a quick and dirty pump with valve set up inspired by the Stuart Turner pumps.

Here's the completed engine side of things as it stands. For info, it has a 5mm bore with a 14mm stroke. It purrs along nicely on about 5psi and will run for some time one one squeeze of a footpump (thats the creaky noise in the video...must oil that one day )

Don't suppose it'll pump much although there's enough poke in it to wobble a finger when you stick it on the business end.

[ame]http://www.youtube.com/watch?v=y0_k2-Z0Qes[/ame]

Very neat little project. Love the video

Nice little project! Looks like you are missing the pump part...?

Chuck

G'day Paul

Lovely little job.

Now the questions.

Is the valve slide connected directly to the spindle with the stops on it?
Is there a valve which separately a controls the pilot piston for the main valve?
Will it self start?

How about a sketch!

The reason for my question comes from having looked in to Westinghouse air compressors and some Weir feed pumps. On these pumps/compressors the main piston actuates stops on a pilot valve spindle. The pilot valve controls the steam to a shuttle which pushes the main valve back and forth to control steam to the power cylinder. This makes the pump/compressor self starting.

Others familair with the Stuart pump may be able to help.

Regards
Ian

Thanks Herbie. Chuck, hehe you spotted the glaring omission :big: - should be along shortly along with steam instead of air.

Ian, its a simple piston or spool valve, the brass bit on the piston rod whacks the 'stops' moving each valve either side of the hole between the valve chamber and the cylinder - nothing complicated!

It will self-start provided the piston is at one end or the other of it's travel, if it's mid-stroke the inlets will be occluded so air can't get to the cylinder.

Sketch attached ;D

Here's the lowdown on the Stuart although that uses a slide valve. Can't see why they're described as 'not forgiving' though...

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

Paul,
When I first go into building model engines all I made was steam and steam related items. I built a setup with several Stuart engines, one of their pumps, a hand pump, boiler, supply tank and dynamo. It makes a nice operating display. As for the 'not forgiving' part I don't know exactly what that refers to but I can tell you this, they are a pain to use. First of all you can't or don't need to run them continually so between cycles they cool down. As soon as you reapply steam to them it condenses so you need to open the drain cocks to let the water out. With this design once they are free of water and working they cycle oddly. By that I mean the piston will run at 2 different speeds, fast when it's returning and slowly when it's pumping. When you're trying to fill a boiler you open up the steam valve and the pump will try to force water into the boiler and the pump will move very slowly so the first thing that you do is open the steam valve a little to speed it up. This works fine but on the return stroke it comes back so fast (because there is no load) that it will cavitate (lose prime). So now it has no water in the pump to push into the boiler so it speeds in both directions (goes into wild oscillations). To correct this you close down the steam valve a little and it will draw in some water and then start the whole cycle all over again.
The cure for this is to build a duplex pump where the load is always constant.
gbritnell

Thanks for that info. The uneven load had crossed my mind before I started on the other project (another simplex pump).

The cure for this is to build a duplex pump where the load is always constant.

Click to expand...

:big: Hehe, got to start somewhere though!

Paul

G'day Paul

Thanks for advice, very useful.

Regarding the uneven strokes with a single acting pump. A solution would be double porting, that is separate inlet and exhaust ports at each end. By reducing the exhaust port diameter at the top end the speed of the returm stroke could be inpeeded.

I have seen a similar design with a latching mechanism on the valve spindle and springs against the stops. The piston has to travel to the full stroke before the spindle is released with spring pressure driving it over. This method makes the pumps self starting.

Regards
Ian

Hi Paul,
Here's a short video of a scratch built duplex pump that I built many years ago. The drawings were presented in one of the home machinist's magazines, live steam etc. This type of pump maintains constant output pressure so it can be regulated down quite slowly and still work properly.
gbritnell
[ame]http://youtu.be/r9FxfK_ZikE[/ame]

:bow: Excellent... if only I had the time, equipment and expertise! :big: