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Old 09-04-2020, 05:24 PM
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Default Underhood rotary air compressor

I ran into a very nice VMAC air underhood 70cfm compressor that I decided I couldn’t live without. It is just the air end, none of the accessory parts. In order to install it I would need a bracket, oil/air separator with coalescing filter, oil cooler, and throttle control.

If I buy all the manufacturers parts new it is somewhere in the 4 grand neighborhood. None of the items frighten me to make them except for the electronic controls. The oil/air separator is marginally confusing as far as how it filters, returns, and scavenges oil, but a unit from any rotary screw compressor would likely work fine, though size and space to install would be a consideration.

The unit is originally set up with lots of electronic controls to raise engine speed, shut off engine when not using air, over temp shut off, cab air temp monitoring, etc. this unit makes enough air at idle for most of my needs, and with the addition of a storage tank would likely be cycled off more than on, so I am not sure that I would even require all the electronic gizmos.

Has anyone ever monkeyed around with these? Installed or operated? Can they be wired with a simple pressure switch through the clutch like an a/c system?

I have attached a picture I stole from the internet of the compressor.

Thanks
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Last edited by Walker; 09-05-2020 at 09:22 AM. Reason: Spelling
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Old 09-04-2020, 07:22 PM
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Whitetrash Whitetrash is offline
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I think it can be done in a even more simple fashion. Rotary compressors aren't really meant to be cycled in and out. They are either on or off. Wire the clutch with a main power switch and employ a pop-off valve to vent excess air while you are using it. Just for safety's sake I would use a tee fitting with 2 pop-offs with slightly different cracking pressures to guarantee system safety.
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Old 09-04-2020, 08:35 PM
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Sounds like a spot for an unloader valve.
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Old 09-04-2020, 10:03 PM
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Quote:
Originally Posted by Norm W View Post
Sounds like a spot for an unloader valve.
A D-2 governor for an air brake system would probably work awesome it would keep system pressure 125 Lbs. Max. All truck air brake compressors run all day long and the D-2 cycles them in and out. They are all old school piston compressors with fairly low CFM. I really think a high capacity rotary will work way better with a K.I.S.S. Pop-off system. Let it run at it's most efficient RPM/ workload and just piss off excess air.
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Old 09-05-2020, 09:20 AM
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Good ideas. I found a regular compressor unloaded that had the cam capacity, haven’t found the capacity of the D-2. Most of the pop offs I have dealt with (mostly Fisher natural gas service) are fairly crude and loud.
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Old 09-05-2020, 09:56 AM
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Quote:
Originally Posted by Walker View Post
Good ideas. I found a regular compressor unloaded that had the cam capacity, haven’t found the capacity of the D-2. Most of the pop offs I have dealt with (mostly Fisher natural gas service) are fairly crude and loud.
They are loud. Sound like a kid with a fart can muffler on his Honda.
A D2 governor is a good idea, and the compressor can be 1200 cfm or 2cfm. All it does is shunt air from tank pressure to lift the intake valves at the pressure set for.

All rotary compressors I have used have a butterfly on the intake to control the air volume pumped. A large throttle plate from a vehicle can be mounted and a little air cylinder controlled by the D2 will open and close it as needed.

Of more concern is the oil separator. I would buy a separator screen, and go look at a VMAC unit and copy the case that the separator sits in.

Also you need to look at the oil injection metering from the reservoir tank to the compressor intake.
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Old 09-08-2020, 06:46 PM
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Well, I was able to find the oil tank with the oil filter, the coalescing filter, blow down cap, etc. for a price I was willing to pay.

The compressor should be here in the next day or two, so I should be able to figure out how the inlet control valve is controlled. I don’t see any mechanical controls on the parts diagrams, so I am guessing it is a pneumatic feedback to open and close the valve.

Need to start looking for a brazed plate oil cooler and decide where and how to mount that. Shouldnt be any big problem due to all the oil cooler failures on the power stroke and duramax engines I am sure there is bound to be aftermarket support there. Then the Engine mount bracket. It looks like they have been mounted in front of the belt drive using a larger crank pulley and an 8 groove belt, or mounted inline with the factory belt drive, add a couple idlers. I think I will likely look at using the factory belt as I don’t need as much air as this can produce, so a slightly lower speed shouldn’t hurt me. So long as I can put on an original length belt if the special order pulley pooched I don’t see any big issues.
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Old 09-08-2020, 07:24 PM
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Quote:
Originally Posted by Walker View Post
Well, I was able to find the oil tank with the oil filter, the coalescing filter, blow down cap, etc. for a price I was willing to pay.

The compressor should be here in the next day or two, so I should be able to figure out how the inlet control valve is controlled. I don’t see any mechanical controls on the parts diagrams, so I am guessing it is a pneumatic feedback to open and close the valve.

Need to start looking for a brazed plate oil cooler and decide where and how to mount that. Shouldnt be any big problem due to all the oil cooler failures on the power stroke and duramax engines I am sure there is bound to be aftermarket support there. Then the Engine mount bracket. It looks like they have been mounted in front of the belt drive using a larger crank pulley and an 8 groove belt, or mounted inline with the factory belt drive, add a couple idlers. I think I will likely look at using the factory belt as I don’t need as much air as this can produce, so a slightly lower speed shouldn’t hurt me. So long as I can put on an original length belt if the special order pulley pooched I don’t see any big issues.
That'll be a great unit for you once it gets running.
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Old 09-09-2020, 09:36 AM
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The York a/c compressor is real popular with the 4x4 crowd. I believe it has an actual crankcase so the oil is not mixed with the refridgerant or air being compressed, although a filter is still recommended.

http://www.offroaders.com/info/tech-...nboard-air.htm

Last edited by NOBLNG; 09-09-2020 at 09:41 AM.
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Old 09-09-2020, 05:08 PM
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Yeah, those York’s are fine for a couple CFm at 80 psi with a 15% duty cycleI already make 24 CFM, and his rotary screw will make 70cfm at 175 at 100% duty cycle.
A lot of guys in four wheel drive clubs will run one to fill up tires in about 10 minutes. I should be able to air up tires for the entire club in about 45 seconds.
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