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Old 07-05-16, 08:52 PM   #1
oil pan 4
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Default More eco gasoline powered air compressor

My beat up old 8 gallon wheelbarrow type air compressor was a scrap yard rescue. It has a steel tank that is on its way out, needs to be replaced and had seized Honda GX160 engine that some one decided to run with no air filter and got rained on and full of water. What can I say there are a lot of idiots where I live.
I sold the GX160 carb, gas tank and cylinder head on ebay for way more than what the whole compressor cost me to buy.
The compressor was and still is good. And it didn't have an unloader valve.
I took a 30 or 40 year old 5hp briggs and Stratton engine and put it on there, with a new unloader valve and it works.
But those air tanks have had it, they need to be chopped up and taken back to the scrap yard.
I have 2 refillable R-134a cylinders that I have been using as extra air tanks, Filled with water they hold right about 5 gallons of volume.
The plan is to use these to make a base for the motor and compressor, weld in bungs to the under side of the tanks so the there will be a drain for water build up.
Then get it hydrostatic tested.

The challenge to make something seemingly inefficient more efficient across a wide operational range, while doing everything from providing air for sand blasting, painting, carbon arc gouging, plasma cutting all the way down to driving wire nails.
First step to make it more economical I am going to replace the very old 5hp briggs and Stratton with a new 5.5hp Honda GX200. Honda claims 25% fuel efficiency increase over the old side valve design.
To make the engine to compressor system as a whole more efficient I am going to put a larger pulley on the engine compared to what I had on the briggs, to drive the compressor close to its 1250rpm limit, producing more air faster, running the engine wide open and more efficiently.
Then to make it highly efficient during low air use add a kill switch to the engine unloader, so if I am only using a little air intermittently say like with a nail gun or need to remove one thing with an impact wrench the engine will shut off once unloader pressure is reached. That way I can start it and walk away.
Normal unloader mode for heavy use will keep the engine running at reduced speed.
I see people run gasoline powered compressors like this to operate a single nail gun and think how wasteful that is. On my 10 gallon electric compressor my nailer can shoot about 40 or 50 full size framing nails 3 inches long at 90psi before kicking on, over 100 shorter 2.5 inch frame nails at 60psi, the roofing nailer only needs 40psi does well over 200 hundred roof nails and finish nailer will shoot what seems like unlimited wire finishing nails before it kicks on again. No reason to run the engine "unloaded" when driving some nails.

Then I will turn the old briggs and Stratton into a water pump, alternator generator or something, not just going to throw it away.
Projected start date is this august.

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Old 07-05-16, 09:53 PM   #2
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Sounds like fun. There are more than a few morons in New Mexico.
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Old 07-08-16, 06:07 AM   #3
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Hydro testing your R-134a tanks is being extra thorough, maybe overkill.

According to the PT chart for 134a, if the tank ever got to over 100 degrees (for instance, sitting in a parked HVAC service truck) then it was holding over 120 psi already. Do you have reason to suspect the tanks have suffered damage?

Granted, if it's going to rupture you want to do it while it's filled with water, not air.

I remember reading, years ago, about a shadetree tinkerer building his own hydro testing rig. It was pretty straightforward as I recall but I can't remember where I read it or even what kind of system he was testing. Knowing your other projects I reckon that would be completely within your capability.

Whoops, just realized your start date is looming. Getting it done is faster than building it done, never mind my last suggestion!

According to Honda's small engines web page, the torque peak on the GX200 engine is right around 2600 psi. It'd be pretty sweet if the compressor's power requirements for your projected operating range lined up with that torque peak; small engines get a lot less obnoxious when you can run them just a little slower.
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Old 07-08-16, 01:47 PM   #4
oil pan 4
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I may test them at work if the hydrostatic tester is back from being repaired, if not I will take it the fire safety supply shop.
At 2,600RPM the engine produces around half the rated horsepower, so it will not be able to run the high demand items.
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Old 07-11-16, 04:10 AM   #5
oil pan 4
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Actually I thought about what you said about running the engine at a slower speed.
Running that Honda engine at a slower speed wont work.
But then I got to thinking if I had a bigger engine it would.
So I found an air cooled 10hp diesel engine, its most fuel efficient at 2500rpm and it makes about 5hp at 2500 RPM.
Only problems is I already bought the Honda engine to build this air compressor and the diesel engine is $800.
The diesel engine also weighs over 100lb and the Honda GX200 weighs about 35lb.
As far as I can tell the diesel engine would burn about half as much fuel as the gas motor.

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air compressor, gas powered, homemade, off grid, roof

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