Small air compressor sufficient to run a Potty Mill

This topic has 16 replies, 14 voices, and was last updated 2 June 2019 at 18:09 by John Duncker 1.

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31 May 2019 at 20:50 #411993
John Duncker 1
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@johnduncker1
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.
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31 May 2019 at 20:50 #26647
John Duncker 1
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@johnduncker1
31 May 2019 at 22:45 #412005
Malc
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@malc
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.
31 May 2019 at 22:49 #412006
Paul Lousick
Participant
@paullousick59116
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.
31 May 2019 at 23:05 #412008
Bazyle
Participant
@bazyle
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.
31 May 2019 at 23:16 #412011
Neil Wyatt
Moderator
@neilwyatt
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
1 June 2019 at 00:45 #412018
Hopper
Participant
@hopper
I've seen similar engines run on an airbrush compressor.
1 June 2019 at 02:21 #412023
John Duncker 1
Participant
@johnduncker1
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.
1 June 2019 at 06:49 #412027
Stewart Hart
Participant
@stewarthart90345
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

Stew
1 June 2019 at 08:57 #412037
Dalboy
Participant
@dalboy
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.
1 June 2019 at 09:37 #412044
Howi
Participant
@howi
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.
1 June 2019 at 11:04 #412057
BOB BLACKSHAW 1
Participant
@bobblackshaw1
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
1 June 2019 at 12:51 #412073
Ian S C
Participant
@iansc
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
1 June 2019 at 13:14 #412075
Gas_mantle.
Participant
@gas_mantle
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
1 June 2019 at 13:27 #412076
Jon Lawes
Participant
@jonlawes51698
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.
1 June 2019 at 14:25 #412081
duncan webster 1
Participant
@duncanwebster1
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
2 June 2019 at 18:09 #412267
John Duncker 1
Participant
@johnduncker1
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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