Building a compressor pump

[Aled Owen]

I've had the idea for some time of building an air compressor, the pump would be belt driven and would be built from a small engine (this model) and would have copper piping to pipe it up to a large calor gas bottle, which would be the reciever.

I've got a small 24 litre Stanley air compressor which I could take the pressure gauge and switches from, rather than buying (because I'm poor) new ones.

I can adapt the engine so air is delivered every two strokes, by blocking the exhaust valve off and running the intake through the spark plug hole, and the pipe to the reciever runs through the intake valve (this can be the other way round), with the valve stuck open all the time.

The pump can be belt driven from some single phase motor (about 3hp) I'd look around for, I'm just wondering if anybody has done this before, and how successful they've been with it. It's main use over my existing compressor would be spray painting, which my current compressor is capable of doing just not very well.

 

[Shox Dr]

Yes it's been done before, on multi cylinder engines, there's a thread no here somewhere. Have you worked out the CFM it will produce?

 

[rtbcomp]

You'll get delivery every stroke if you make the both valves permanently closed and use a couple of non return valves connected to the plug hole for inlet & outlet.

Make sure you keep the oil pump working though.

 

[tigler]

Compressors made from converted engines are a common project, I've seen quite a few on youtube. Just reading your proposal throws up a problem, unless I'm missing something. Intake through the spark plug hole and exhaust through a stuck open inlet valve won't work, unless, a valve is incorporated on the intake. If not, air cannot be pumped as it will just exit the plug hole intake.

 

[Aled Owen]

Compressors made from converted engines are a common project, I've seen quite a few on youtube. Just reading your proposal throws up a problem, unless I'm missing something. Intake through the spark plug hole and exhaust through a stuck open inlet valve won't work, unless, a valve is incorporated on the intake. If not, air cannot be pumped as it will just exit the plug hole intake.

hehe, forgot to mention I'd be using no-return valves on the intake port and on the port to the reciever. Should that fix the problem?

 

[tigler]

As long as the one in the outlet can withstand the temperature.

 

[rtbcomp]

It would still be easier to use both the NRVs on the plug hole rather than connect one to the inlet.

 

[Aled Owen]

It would still be easier to use both the NRVs on the plug hole rather than connect one to the inlet.

And use something like this to connect the two no return valves up to the plug hole with?

 

[rtbcomp]

Yes. IIRC the thread on 15mm compression fittings is 1/2 inch BSP, so you need NRVs with 1/2 BSP female threads.

 

[Aled Owen]

I've got a potential pump for the compressor, is there a way to roughly work out the CFM of the pump based on the bore and stroke?

Cheers

 

[rtbcomp]

Cross sectional area in feet² of the bore multiplied by the stroke in feet gives swept volume per revolution in cubic feet. Multiply this by rpm to get the FAD in cubic feet per minute.

 

[eil]

Aled, have you thought of a way to get rid of the engine`s combustion chamber, as with the combustion chamber and the space up to your T piece there will be a lot of room for compressed air to be left in the cylinder and when a certain pressure is reached the suction and discharge valves wont open, as you will have too much pressure in the cylinder on the down stroke for the suction to be kept closed and not enough pressure on the up stroke to open the discharge. Compressors need the valves as near as possible to the top of the piston and the least room as possible between piston and valve plate or you will have poor free air delivery.

 

[Lawnmowerboy]

What's the cc and compression ratio?

 

[Aled Owen]

Aled, have you thought of a way to get rid of the engine`s combustion chamber, as with the combustion chamber and the space up to your T piece there will be a lot of room for compressed air to be left in the cylinder and when a certain pressure is reached the suction and discharge valves wont open, as you will have too much pressure in the cylinder on the down stroke for the suction to be kept closed and not enough pressure on the up stroke to open the discharge. Compressors need the valves as near as possible to the top of the piston and the least room as possible between piston and valve plate or you will have poor free air delivery.

Yeah that's one of the problems I've been thinking about, I was thinking of modifying the cylinder head but I don't want to ruin the engine, incase I want to turn it back into an engine in future, a solution will come, damn these side-valve engines haha.

There's always the slim possiblity of building a special cylinder head for this purpose from plate mild steel on a milling machine but I'm not sure how reliable it'd be.

 

[Aled Owen]

What's the cc and compression ratio?

170cc and I'm not sure of the compression ratio, the engine is a Tecumseh H50, just trying to do a bit of research into it now.

Cross sectional area in feet² of the bore multiplied by the stroke in feet gives swept volume per revolution in cubic feet. Multiply this by rpm to get the FAD in cubic feet per minute.

About 11.8cfm at 2000rpm if I'm right, the bore and stroke are 60mm each.

 

[shenion]

Cross sectional area in feet² of the bore multiplied by the stroke in feet gives swept volume per revolution in cubic feet. Multiply this by rpm to get the FAD in cubic feet per minute.

That will be the displacement, not FAD.

FAD is the actual output after losses due to volume of chamber and blow by the rings..

170cc gives displacement of 12CFM.

The smaller volume you can make the chamber, the more efficient it is and the higher PSI it will support. The piston must compress the air in the chamber up to the tank pressure before any air will flow out.

 

[Aled Owen]

The smaller volume you can make the chamber, the more efficient it is and the higher PSI it will support. The piston must compress the air in the chamber up to the tank pressure before any air will flow out.

Well in that case I'll build a custom cylinder head, I've got access to a Milling Machine at college, but it'll be Mild Steel, whether or not it'll be able to to withstand much use or not is a different question, one shouldn't be too expensive to build though.

What sort of speed does the pump run at?

 

[rtbcomp]

Few hundred rpm

 

[eil]

Well in that case I'll build a custom cylinder head, I've got access to a Milling Machine at college, but it'll be Mild Steel, whether or not it'll be able to to withstand much use or not is a different question, one shouldn't be too expensive to build though.

What sort of speed does the pump run at?

The speed will be determined by the power of your electric motor and what pressure you expect it to go up to and the pumps CFM