Demon water motor (OT?)

I managed to get the side cover off of my Astle purchase during my lunch hour today and it contains a pelton wheel of about 8" diameter. I recalled seeing something similar in SEM not too long ago and a little searching turned up a query from David Edgington in Engine Torque together with a reply a couple of issues later. The device there shown appears to be somewhat smaller and cruder (a plain paddle wheel rather than properly shaped buckets) and was apparently intended to be powered from the water mains for light duties such as charging ones wireless accumulators. I wonder what you can do with an 8" pelton?

Due to the state of the fixing bolts I thought I was in for a long fight, a combination of rust and abuse meant that they barely boasted a good flat among them and certainly no longer fitted any standard spanner. A couple came out with an adjustable, but most were very reluctant to move and I gave up at the first sign of slipping not wanting to risk my knuckles or make the bolt heads any worse. Then my eyes alighted on one of those one-size-fits-all things, the sort which look like a deep socket full off spring loaded rods, lying unused in the bottom of the tool box. I don't even know why I own such a thing after all these catch-penny devices never actually work, but I tried it more in hope than expectation and blow me if it didn't get a really good grip on all but one of the bolts, again I gave up at the first sign of slipping. The last one was finally persuaded to give up by clamping it in the vice and rotating the casing. No swearing, loss of blood or broken metal, why can't all rusty iron come apart like this - or would that be too boring?

Reply to
Nick H
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I have put a few pics of the beastie on webshots (other stuff album).

BTW gasket between two halves appears to be lino with pattern still just about visible in places!

Reply to
Nick H

You can generate electricity. I know where a hill farm in Mid Wales has one in use powered by the local stream. Not sure of the size or electrical output. I last saw it only a couple of years ago and it was running well then.

John

Reply to
John Manders

Anybody like to hazard a guess at the age of the device? I found the website of a guy in the 'States who collects antique Pelton wheels

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we thought our hobby was obscure!) which states that Lester Pelton patented his split-bucket wheel in 1889. So I guess it could be any time after that, but probably after the patent expired (25 years?).

Reply to
Nick H

Just ran it up on the end of the garden hose - made 1200 rpm, a fair bit of torque (judged by grasping shaft) and a pleasant low humming noise. A quick bucket test showed that it was flowing just over 2 gals/min - don't tell the water company;-) With nozzle diameter of just over 1/8" (number 30 drill possibly?) I'm sure I should be able to calculate the velocity head and hence available power in jet - I'll work on that one.

Got to go and dy out my pocket tacho now!

Reply to
Nick H
2 gals/min = 9.25 cubic inches per sec. Which, through a 0.1285 in hole (No 30 drill, area 0.01297 square inches) equates to a nozzle velocity of 713.26 inches per sec. Velocity head = velocity squared / 2g = 659 inches = 55 feet. (g = 386 inches per second per second. One horse power is 33,000 foot pounds per minute and 1 gal of water weighs 10 pounds so power in jet = 20 x 55 / 33,000 = 0.03333hp

Told you it was powerful - and that's assuming 100% nozzle and turbine efficiency!

I am open to correction on the above (it's been some time since I attempted 'ard sums) and indebted to

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the various conversion factors.

Reply to
Nick H

Nick,

You sad individual :-))definitely got time on your hands :-))

Martin P

Reply to
Campingstoveman

OK. I'll shut up now, it may be stationary and a sort of engine (and fun), but I guess it is a bit OT.

Reply to
Nick H

Don't see why and in any case it is, like tractors, well within the wide interests of most of this group. ttfn Roland

Reply to
Roland and Celia Craven

Nick there were smileys on the previous post.

I for one find all posts on early power generation interesting (tractors too!). If the sums had been in SI units I may have been sad enough to check them.

This is why i liked the theme Paul Evans has the germ of in his engine museum.

BTW Paul thanks for the time you spent with me when I visited. I was particularly pleased with the "surface ignition" engine and the novel starting method, and what a lovely sound.

AJH

Reply to
sylva

Don't worry, I know Mr. P and no offence was taken ;-) You'll have to try harder Martin!

Reply to
Nick H

Now where shall I start, having just been handed the loaded weapon :-)) Off to the rally for the weekend Bye Bye.

Martin P

Reply to
Campingstoveman

That equates to 24 Watts. That doesn't sound a lot from a 8" turbine. Then again, 2 GPM is not a lot of water.

Also, one of the design features of the Pelton wheel is that it returns the water in the opposite direction to the jet thus gaining more power. Your calculation hasn't allowed for the energy in the exhaust water. This isn't double as the wheel is moving but a significant increase can result. The bucket speed is 1200 RPMx8x3.142/60 = 502 in per sec Therefore (ignoring friction) the water jet has +713 in per sec out of the jet and -(713-502=212) in per sec in the exhaust stream. The change in water velocity is therefore 713+212 = 925 in per sec. Feeding that into your calculation gives a theoretical power of .0432 HP or a whole 32 Watts. That's a 30% increase. Thinking further, Power = pounds force x velocity change Force = weight x gravity Power = mass of water per sec x g x velocity change (feet per sec) Power = 20/60 x 32 x 925/12 = 822lbf ft/sec = 1.5 HP As with you, It's been a long time since I did these sorts of sums so I could be totally wrong. Please feel free to correct me. Having made my brain hurt I shall go and lie in a darkened room.

John

Reply to
John Manders

Any energy remaining in the exhaust water is wasted. Maximum power transfer occurs when peripheral velocity of the wheel is half that of the water jet so, from the frame of reference of a bucket, the water jet hits it at half the jet speed and is indeed turned around to leave in the opposite direction at the same speed. But, from the frame of reference of the rest of the world, the velocity of the water is now zero hence no wasted energy. It's like throwing yourself off the back of a slow moving train - if you can jump backwards at the same speed that the train is moving forwards you will hit the ground vertically (don't try this at home!)

Here endeth the first lesson ;-)

Reply to
Nick H

I think with a suitable head an 8" (200mm) turbine will do a small number of kW. They are also made with more than one nozzle and cast in plastic nowadays (though I see some bronzeish ones are available also).

Sort of but the whole point of the Pelton wheel is that the cups turn the water jet through 180 degrees, this is to extract all its momentum. So the ideal is to have the water drop off the wheel at zero velocity, this it can only do if the bucket is moving at half the speed of the water jet, so ideal power matching is at this speed and is a function of nozzle, head and torque of output (which is also power as torque times revs is power and revs is set by this velocity relationship).

Pelton wheels reach remarkable efficiency of conversion and the story of there uptake is over simple wheels is testimony to this.

AJH

Reply to
sylva

volume flow rate = 0.000152 m^3/s

mass flow rate = 0.152 Kg/s (density of water = 1000kg/m^2)

nozzle dia = 0.003264m, area = 0.000008366m^2

nozzle velocity = vol flow/area = 18.167 m/s

velocity head = v^2/2g = 16.82m (g = 9.81m/s^2)

power = mass flow rate x g x head = 25.08w

Again many thanks to

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Reply to
Nick H

wrote (snip):-

Hooray, the result will still be valid on Venus then ;-)

Seriously though, yes looking at it you are quite right, maths never was my strong point, I just tend to knife and fork my way through things in an vaguely intuitive fashion, and the intermediate result of velocity head gave me some sort of handle on how much shove was coming out of our water main.

Useful, though overall dia is actually about 7 1/2" and pcd of buckets around 7" (0.558m circ). Does show how much below expected free speed wheel was running though - bearing friction, windage etc etc?

I believe such a sytem has been used to match relatively constant generating capacity to demand with a high peak to mean ratio, though on much larger plant.

Reply to
Nick H

Probably hard to tell once everything has been mixed up in the national grid. I'm always amazed when I get offered the opportunity to purchase my electricity from a sustainable supplier - I would want little labels on all the electrons to prove where they had come from! Having said that, I am a bit of a closet greeny in that I do think out profligate use of energy can't go on for ever. How you square that with a load of engines sitting in a field burning fuel to do nothing at all I don't know, but I never said I was constant ;-)

Reply to
Nick H

gravity term not needed as it cancels through, your head term was a derivation from the equation 1/2*m*v^2=m*g*h.

unit volume flow rate 0.000152 m^3/s mass flow rate 0.152 kg/sec nozzle dia 0.003264 m nozzle area 8.36739E-06m^2 nozzle velocity 18.16575307 m/sec energy/sec 25.07958842 W pelton circ 0.62831853 m pelton rpm 867.3508187 rpm

cut from excel

Now how about a ball park estimate of whether it would ever be worth using the difference in specific fuel consumption of our stationary lister genset at low demand to more fully optimising its generating efficiency by pumped storing water and then using a pelton wheel to fill in whilst the engine is idle? I've already done the calculations for a battery and inverter and it pays to keep the generator running, simply because the storage cost exceeds the generation cost.

AJH

Reply to
sylva

Yes but the head would be different to achieve the same velocity.

Yes Dinorwic but does this use baseload electricity from nukes? Or is it fed by windpower?

In our case we should have specified two gensets as we only average

2kW and should not really run the 10kVA set so lightly loaded.

AJH

Reply to
sylva

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