Engine Air Compressor?

AKwelder · Feb 4, 2009

There have been several of these rigs on spread that i worked over the years, and they all have one thing in common, different heads. Some had special pistons in the compressor cylinders. They all were used in high flow applications. But by having more compressor than we needed we got high PSI.

I am sure that you could modify a cylinder head to work, but you might want to sure that the engine you are using has good cooling, not an engine that has a history of over heating.

The unloader is a big deal, make sure you have a large enough one.

running of a belt sounds like less work, yet may still be exspensive

Redneck in training · Feb 4, 2009

Iplayfarmer said:
I guess one of the things I'm shooting for is to lower the power consumption. I was guessing that if each of the pistons were only compressing the air halfway (i.e pistons 1 and 2 are taking it from 0 to 50 psi and piston 3 is taking it from 50 to 100) it would lower the power consumption. It would also lower the output, but it seems pretty well accepted amongst us that for the task at hand this setup would be more than sufficient.

By increasing the dead space to change the compression ratio like you suggest would it also decrease the amount of heat created? Even if it didn't would the heat created be more that normal operating temperatures of an engine. You'd have the radiator and engine cooling system there that could be used to cool.

It will not decrease power consumption. The power equals to mass flow of air times head. You can substitute pressure ratio for head to see that doubling pressure ratio will approximately double the power consumption (Ignoring effect of temperature). The power consumption will go actually up due to higher mechanical losses. High pressure ratio compressors have to be multistage exactly due to temperature control. If we would have materials that can handle high temperatures theoretically we could build single stage compressor for any pressure ratio.

Iplayfarmer · Feb 4, 2009

Redneck in training said:
It will not decrease power consumption. The power equals to mass flow of air times head. You can substitute pressure ratio for head to see that doubling pressure ratio will approximately double the power consumption (Ignoring effect of temperature). The power consumption will go actually up due to higher mechanical losses. High pressure ratio compressors have to be multistage exactly due to temperature control. If we would have materials that can handle high temperatures theoretically we could build single stage compressor for any pressure ratio.

I'm thinking you'd aim for 120 PSI vs. the 100 that we've all been talking as a theoretical limit of a single stage in this system.

The reason I was thinking that power consumption would go down is exactly because of that head that you are talking about. What the trade off would be is giving up volume for a little more pressure and less power consumption. My approach is that none of the pistons in a two stage setup would work as hard as they would have to in a single stage setup.

Of course another option for trading volume for power consumption would be to just run the engine slower.

Egon · Feb 4, 2009

Rod loading.

bobodu · Feb 4, 2009

It's a simple matter of physics...storing energy requires energy.
Lessay you wanna lift a ten ton truck.You can use this jack and give it ten hard pumps or you can use that jack and give it fifty easy pumps....at the end of the day you still would have exerted the same amount of energy....

CCWKen · Feb 5, 2009

I was lucky and found a used Sullair 160 for less than a 1/3 of what I paid for the shop compressor. All it needed was a few adjustments, the cover assembled and a new thermostat. I use it for sand blasting. It outputs 160cfm @ 125psi. The twin screw compressor is powered by a GM 4-cylinder industrial engine. More than enough for even the largest shop and plenty for my blasting needs. The only time it hits full throttle is when I open the air valve to fill my blasting tanks. It can fill an 80 gallon air tank in about 4 seconds.

Bishop · Feb 5, 2009

The Reciprocating Compressor Division is involved with the design, development and manufacture of single and two stage reciprocating compressors. The following are the range of compressors developed at the Reciprocating Compressor Division.

Iplayfarmer · Feb 5, 2009

bobodu said:
It's a simple matter of physics...storing energy requires energy.
Lessay you wanna lift a ten ton truck.You can use this jack and give it ten hard pumps or you can use that jack and give it fifty easy pumps....at the end of the day you still would have exerted the same amount of energy....

Understood. I'm using physics too in that if you do less work (i.e. less volume) you use less energy.

BrentD · Feb 5, 2009

Maybe I'm just being thick, or maybe my brain has just decided to burn out from the monotony of my day job, but I keep coming back to the pressure question. I sort of understand what you guys are saying about the 100psi not being realistic, and until this morning I was pretty much sold on the argument. Then I thought about the compression test again.

A compression tester is just a pressure gauge with a schrader valve that you thread into the spark plug hole. The engine cranks a few times and the gauge goes up until it hits a point where the engine can no longer generate enough pressure to open the schrader valve. On the particular 4-cylinder engine I was testing each cylinder tested between 150 and 170 psi.

In the compressor application I understand that the engine would lose a little bit of compression based on the amount of pipe between the spark plug hole and the check valve, but surely it won't be that much.... And the pressure in the line and tank will be cumulative. Shouldn't you be able to achieve a tank pressure equal to at least the compression of the weakest cylinder?