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The Monoblock Air Compressor Resource Thread

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OccupantRJ

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This thread will be similar in function to my Abrasive Blasting thread in the sense that it will be a repository for information on a specific tool, the monoblock air compressor.

For the uninitiated, a monoblock compressor is made from a standard automobile engine, usually a flathead or overhead valve engine. One of the cylinder heads is replaced with a special air compressor style head usually with valves of the concentric plate valve design.

The engine runs as normal on half the cylinders and the other half is used as a high volume air compressor.

I have one of the Gordon Smith 302 Ford V8 compressors which I will provide a link to. Feel free to add your own pictures, experience, and other tidbits of information relative to this type of compressor.

I have been doing patent research to garner information, and will be adding that along the way as time allows.

Enjoy, and I hope this thread provides some good information that someone may be able to use to upkeep, repair, or build their own unit.
 
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OccupantRJ

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This is the link to when I bought my monoblock compressor. This one is the second unit I have owned. The previous unit was a 6 cylinder Chrysler inline monoblock, and as I remember was about 75 CFM. I did quite a bit of blasting on automotive projects for my self and others during that time period.

I eventually sold the unit, and have mentally kicked my self ever since. That was the reason for the acquisition of the 302 unit. I have started posting facts and observations about the compressor in the link below to hopefully help others with the same unit.

http://www.garagejournal.com/forum/showthread.php?t=322952
 
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Al Borland

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a buddy has one with a generator attached on what would be the transmission end.
 
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MacMcMacmac

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There are also the LeRoi Tract-Air and Schramm Pneumatractor compressors.

I have also seen one made from a CAT V8 good to 1500psi.

And these old IR radials:

 
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OccupantRJ

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The Smith 100D monoblock compressor uses a Clippard 3SS-1/2T miniature air cylinder as the throttle actuator. 3/8" bore, 1/2" stroke, 10-32 threaded rod. Took a bit of research to get the identification figured out.
 
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OccupantRJ

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This is information on the operation of the monoblock compressor written by David Smith, grandson of Gordon Smith, originator of the Gordon Smith air compressor.

The compressor is designed to build pressure to 100-105 psi and then unload. When the pressure drops to 80-85 psi the system should start producing air again.


How it should work:


The Pilot valve (air pressure adjust) controls when the system loads and unloads. The two steel lines coming from it go to the carb air cylinder and the compressor valve unloader pistons. Be sure the sintered bronze air filter (located on the end of the pilot valve that screws into the head) is not clogged. When the pressure builds to 100-105 psi the pilot valve directs some air to the carb cylinder to shut it down to an idle (approx. 800 rpm).

Air is also directed through the Flow Control Valve (bleed down speed) to the unloader pistons above each compressor valve causing them to hold the intake disk open.With the intake disks held open the system is unloaded and will not produce more air. When the pressure has dropped to 80-85 psi the pilot valve vents the air from the unloader circuit. This allows the carb cylinder to open the throttle (to approx. 1600 rpm).

The air from the unloader pistons is retarded by the Flow Control Valve to allow the engine to get a head start before the system starts building air pressure again. There is not a precise setting to the FCV, adjust the screw in to allow more engine head start and out if the engine seems to over rev.

From your description of the system you are working on I would say that the pilot valve is out of adjustment and that your flow control valve is not working. Replace the FCV and adjust the pilot valve to unload at 100-105 psi and load at 80-85 psi.




David L. Smith
 
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OccupantRJ

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My compressor was shutting down after the flow was shut off instead of unloading. I turned the bleed down flow adjuster valve a half turn to the right to slow it down a bit, and the unit started unloading properly. I had previously removed the air pressure adjust and set it to the desired operation point by cleaning it and setting it using the shop air with a regulator to get it dialed in to trip at the desired setting. The valves are labeled in the picture above. The bleed down valve is a commonly used pneumatic valve that free flows in one direction and slows flow in the other.
 
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