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Small air compressor sufficient to run a Potty Mill

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John Duncker 131/05/2019 20:50:07
32 forum posts

I need a small air compressor sufficient to run a Potty Mill 16 mm bore 32 mm stroke

Will this sort of thing do do ?

LINK TO COMPRESSOR

I suspect not.

I guess I can use it to build up some pressure in an air reservoir [ plastic coke bottle ] then use that.

Space and weight matters as my workshop is a tiny cubbyhole on a boat.

Malc31/05/2019 22:45:06
60 forum posts
5 photos

Hi John, I have just finished building a beam engine the bore of the piston is 30mm and the stroke is about the same. I was faced with the same question of how small a compressor could I use to test run it. I only had one of those tyre inflation jobs so I tried it plugged into the 12 volt car supply but it was not quite keeping the engine running - almost but not quite! I have a PSU which I made up to run a cordless drill which had a dead battery it produces about 18 volts. I hooked up the tyre compressor to the PSU and it increased the speed sufficiently to test run the beam engine. A bit cruel on the tyre compressor but it was only for a test run. It was suggested by someone on this forum that a tank such as a plastic bottle would help. Don’t know how your Potty Mill compares to a beam engine? But I thought this little tale might be of interest. Good luck with it,

Malc.

Paul Lousick31/05/2019 22:49:01
1151 forum posts
492 photos

You need a compressor that delivers a high volume of air at a lower pressure. These are the opposite. 300 psi in a coke bottle ! (wear safety glasses when it goes boom).

Do a search om MEW. Lots of previous posts about the same thing.

Paul.

Bazyle31/05/2019 23:05:49
avatar
4686 forum posts
186 photos

An ebay compressor actually delivering the advertised pressure?
What you can do is pump up your spare tyre to the safe pressure of course and then use that as the reservoir for a minute or two. I remember my badger airbrush came with an adaptor for just that. Lasted about long enough to paint one wing.

Neil Wyatt31/05/2019 23:16:36
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Moderator
16435 forum posts
685 photos
74 articles

I suspect it will, because they go round at about 4,000 rpm and the Potty Mouth Engine will go round at about 180rpm on a few PSI.

But it will probably wear out in twenty minutes. In my experience they have about one tyre's worth of inflation in them.

Even 'quality' inflators (I had a Michelin among others) don't have much of a lifetime unless used for light topping up. They overheat and soften the plastic then things just go downhill.

Neil

Hopper01/06/2019 00:45:45
avatar
3657 forum posts
72 photos

I've seen similar engines run on an airbrush compressor.

John Duncker 101/06/2019 02:21:56
32 forum posts
Posted by Malc on 31/05/2019 22:45:06:

Hi John, I have just finished building a beam engine the bore of the piston is 30mm and the stroke is about the same. I was faced with the same question of how small a compressor could I use to test run it. I only had one of those tyre inflation jobs so I tried it plugged into the 12 volt car supply but it was not quite keeping the engine running - almost but not quite! I have a PSU which I made up to run a cordless drill which had a dead battery it produces about 18 volts. I hooked up the tyre compressor to the PSU and it increased the speed sufficiently to test run the beam engine. A bit cruel on the tyre compressor but it was only for a test run. It was suggested by someone on this forum that a tank such as a plastic bottle would help. Don’t know how your Potty Mill compares to a beam engine? But I thought this little tale might be of interest. Good luck with it,

Malc.

Thank you for confirming that it is possible. I have a PSU that delivers 17 volts and I can try that.

I only want to run it for a couple of minutes at a time just long enough to enjoy the fruits of my labors.

I will probably charge a pop bottle up to 30 - 40 psi and shut the compressor off as they are noisy little suckers and that way I can listen to my running engine.

Stewart Hart01/06/2019 06:49:34
avatar
Moderator
602 forum posts
301 photos
Posted by John Duncker 1 on 31/05/2019 20:50:07:

I need a small air compressor sufficient to run a Potty Mill 16 mm bore 32 mm stroke

Will this sort of thing do do ?

LINK TO COMPRESSOR

I suspect not.

I guess I can use it to build up some pressure in an air reservoir [ plastic coke bottle ] then use that.

Space and weight matters as my workshop is a tiny cubbyhole on a boat.

Yes it should I've run my engine on one. also used it to run my twin cylinder over crank engine that has a far greater cylinder volume.

Try inflating a child frog hopper bouncer and couple it up:- to increase pressure just get some one to sit on it smiley

Stew

Derek Lane01/06/2019 08:57:22
avatar
200 forum posts
48 photos

You will find that most compressors(not all) will deliver 100psi but can be reduced using the regulator.

I personally would look for one that has a reservoir if you are looking for something quite how about something like the compressors for air brushing, depending on what is needed.

Howi01/06/2019 09:37:49
avatar
257 forum posts
15 photos

if you do not want the expense of a suitable compressor (best is low pressure high volume type about £50) you might want to try a fence paint sprayer from such as ALDI for < £10, pumps up by hand up to 3 bar or 40-50psi and more air volume than a coke bottle.

BOB BLACKSHAW01/06/2019 11:04:31
192 forum posts
35 photos

I have made two potty mll engines and have had both running together on a nebuliser. I have found that the nebuliser has the pressure to run the engines at a gentle speed.

Bob

Ian S C01/06/2019 12:51:11
avatar
7444 forum posts
230 photos

I have a Nebuliser compressor, it will pump up about 30 psi, the volume is not great, I know that it is not quite up to running a Stewart Turner S9, niether is a 12v tire pump run on 18v.

Ian S C

Gas_mantle.01/06/2019 13:14:33
avatar
359 forum posts
269 photos

A lot is going to depend on how accurately machined your engine is, provided it turns over freely and has decent compression the compressor you mention should run it for short demo purposes under no load. I suspect at that price the compressor will be poorly made and probably prove unreliable for anything more than a few minutes light running though.

I built a potty mill a few years ago, mine isn't the most accurately machined engine in the land but it turns over freely and does have a piston ring, gaskets etc. It easily runs on one of these, admittedly they are a bit more expensive but that compressor will run the engine indefinitely and at a fairly high speed under a light load if need be

Jon Lawes01/06/2019 13:27:41
avatar
318 forum posts

To think outside the box a little, what sort of boat? Is it a narrowboat or similar? Does the engine of the boat already have some sort of compressor for running other components? Could you find something that would run off of there? Or even have an engine driven compressor feed an accumulator? The compressor doesn't need to be where it is being used, and a pipeline between the compressor and point of use just serves as extra pressure storage if the regulator is done at point of use...

I know its all a bit random, just trying to look at other options for you.

duncan webster01/06/2019 14:25:31
avatar
2201 forum posts
32 photos
Posted by Bazyle on 31/05/2019 23:05:49:

An ebay compressor actually delivering the advertised pressure?
What you can do is pump up your spare tyre to the safe pressure of course and then use that as the reservoir for a minute or two. I remember my badger airbrush came with an adaptor for just that. Lasted about long enough to paint one wing.

My VW beetle (old style air cooled monstrosity) ran it's windscreen washer off the spare tyre, as Baz says pump it up to max rated and check it every time you fill up

John Duncker 102/06/2019 18:09:51
32 forum posts

Thank you for the out of the box thinking. The boat is a 44 ft cutter with a venerable Japanese built Perkins 4-154. Alas there is no engine driven compressor.

My boat does not have a spare wheel. It does have an inflateable dinghy and pump, however the max tube pressure is around 5 psi.

In the past I have used plastic bottles to store compressed air. A typical 2 liter pop bottle bursts at around 120 psi so keeping to about 30 psi is usually safe.

I will probably make a first run directly off the little EBAY pump and only go down the silent pop bottle route later. I can make a widget to vary the air supply from the bottle.

I am in the West Indies and it is easier and cheaper to buy stuff in the USA and ship it down as one consolidated load all marked spares for yacht in transit. This gets me a much lower import tax band.of 2 or 2.5 %

Also some sellers refuse to ship outside the lower 48 states of the USA.

So I am doing some careful planning

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