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1/12 scale beam engine

Compressor power

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Roy Thompson 205/03/2022 14:37:18
2 forum posts

I am not an engineer of any kind just a complete novice but the proud owner of a beam engine that has been gifted and sent to me by my Australian model engineer friend. All I want to know is how can I demonstrate this beautiful model to my friends?

Obviously I realise I need a compressor and so far I’ve tried tyre pressure pumps plus a twin piston engine. I have had it running with the kindness of my neighbour who brought his 11/2 hp machine over and it worked - but of course I only want a small portable pump and his is much too big and heavy.

I have seen a lot 1/6th hp machines on eBay made for airbrushing - these have a storage tank, twin pistons, and are supposed to keep the pressure constant in the tank. I’ve written to one of manufacturers but they said it was only meant for airbrush work? My Australian friend thinks it maybe powerful enough?

So I’m now in a world I know nothing about really and have come to you for hopefully some good advice on a light and portable pump to get my engine running and I can get my bragging rights operating!!

Regards Roy Thompson

Bob Unitt 106/03/2022 12:22:40
222 forum posts
33 photos

I used to use the spare wheel of my car - pump it up at the garage, make an adaptor with a tap on it  to go on the tyre valve, and use a bit of hose to connect the adaptor to the model. Not sure if it would give enough pressure to run your model for a reasonable time, but it worked for me before I got a compressor.

Pro-tip - don't get a puncture on your way back to the garage to refill your tyre... wink

Edited By Bob Unitt 1 on 06/03/2022 12:25:06

Former Member06/03/2022 12:43:54
1085 forum posts

[This posting has been removed]

SillyOldDuffer06/03/2022 13:10:15
8906 forum posts
1999 photos

Hi Roy and welcome to the forum.

There's a bit of an awkward gap in the world of air pumps. Engines need a good volume of medium pressure air. Unfortunately car pumps produce low volumes of high-pressure air, and fans produce large volumes of low volume air. Aquarium pumps are a bit low on pressure and volume.

Bob recommends using a car tyre as a reservoir. The pressure is a bit high and unregulated, but there's a reasonable amount air available. I've used a plastic lemonade bottle and car foot-pump to prove an engine will turn: not ideal!

These days I use a small electric workshop air compressor similar to this one:

These have a largish reservoir tank and a pressure regulated output that can be set to suit the engine. Start at about 5psi and work up for reasonable running. Note a car tyre starts at about 30psi and comes down, unregulated.

The downside of workshop compressors is cost, noise and space! Quiet domestic demonstrations of an engine really need something quieter. A spray paint compressor might do the job, but I've never tried one. Perhaps someone else has a suitable recommendation.


JasonB06/03/2022 13:16:09
23076 forum posts
2771 photos
1 articles

So much will depend on the individual model. A well made one with no tight spots will happily tick over at 30-40rpm on just a couple of psi for display purposes so will not need much in the way of a compressor. On the other hand one that is tight, has the odd leak and needs to run fast so there is enough momentum to carry it over TDC and the tight spots will need higher pressure and the increased revs will mean you also need more volume of air

Something the size of the Stuart beam if made reasonably well will run off a diaphram type airbrush compressor but they tend not to have storage tanks so run all the time and are also noisy. one of the "quiet" ones that are about these days with a small tank would be a better bet provided the engine is built reasonably well.

Saxalby06/03/2022 14:35:58
182 forum posts
26 photos

I run my Stuart Beam engine, and all my other little engines, from a Revell air brush compressor (quite running with a reservoir tank). Can get it going nice and slow at about 5 psi.


Jim Nic06/03/2022 15:04:02
388 forum posts
220 photos


Perhaps a good place to start would be to try and estimate what your model needs for it to run. You have already had it running so you know what pressure it requires to run to your satisfaction.

The other thing you need to know is what volume of air you need. You can work this out if you know the dimensions of the model's cylinder; from this you can work out the volume of air you need per revolution (twice the volume of the cylinder) and from this and the speed you wish it to run at the amount of air you need. Compressors normally have what is known as Free Air Delivery in their specification which is the amount of air it is capable of giving you.

From all this, you can look again at available compressors.

Hope this helps


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