Very Old Curtis Air Compressor Control
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  1. #1
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    Default Very Old Curtis Air Compressor Control

    My project to set-up overhead shaft driven machines in my garage is ever changing. I started with a Universal Tool and Cutter Grinder and bench grinder, but I now have a 14" lathe that will be on the same shafting, so my power source is growing. While I'm at it, I found a very old Curtis air compressor that is, you guessed it, flat belt drive. It has a newer Barber Coleman tank and newer motor, so it's really just the compressor head itself that's the jem. I'd like to power it from the same overhead shafting and could use some help.

    The compressor head has two side-by-side flat belt flywheels, one idle and one driven. The original owner says it originally had a hit-n-miss motor to run it and that the operator would manually switch the flat belt on and off of the driven wheel. I'm wondering if there would be a way to automate that process without too much risk or modern technology, and do so mechanically without any electricity. The reason for this is that the overhead shafting is always spinning and without an electric motor that can be easily turned on and off, I need a way to turn off the compressor when the tank gets up to pressure.

    I could do it with a double acting pneumatic cylinder, but each action would need to happen only at the set pressure and not gradually so I'm thinking I need an air activated two way valve with one or two regulators that only let air by at a set PSI.

    The easiest way would of course be to skip the Rube Goldberg show and keep the control in the hands of the operator, I'm just looking at options that would keep it working like a normal compressor.... but mechanically....

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    not rube goldberg at all, you need a pilot valve from a gas compressor and a spring return single acting cylinder. plumb the idle control port of the pilot valve to your cylinder to flip the belt.

    good article by rolair:

    How It Works: Piloted Unloader Valve - Rolair

    as with any compressor be sure your safety valve is tested and in good repair.

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    use one of these to push the belt over to the free wheel when the pilot trips, the spring will pull it back.

    McMaster-Carr

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    Clutched pulleys on the line shaft were common (Images at line shaft clutched pulley at DuckDuckGo ). While not authentic in terms of a loose pulley, it could be done with minimal modern technology. I think you could use a piloted unloader valve and a spring loaded cylinder on the clutch lever. You'd have to investigate further to be sure.

    I see I type too slowly.

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    Great! So I'm not crazy! I had been sketching out pneumatic concepts thinking "it shouldn't be this complicated."

    I'll order a piloted unloader valve and we have several pneumatic cylinders that should work for this project. The main motor and overhead shafting is still being put together, so I'm going to use the compressors electric motor to prove the concept first. I imagine that the most complicated parts will be the bracket to hold the cylinder and the belt fork.

    Since there may be little to no pressure to activate the belt control, I'll set-up the cylinder to at rest have the belt on the driven pulley, and at high pressure it will activate the shift the belt off.

    The tank is a horizontal 20 gal. and does have a bit of rust on the bottom with a pin hole in one spot, so I'm looking for a replacement and I will likely use a vertical tank since I don't need a place for a motor. The tank will likely anchor onto the same platform that my tool and cutter grinder sits on.

    I'll get some pictures of everything as it comes together.
    Last edited by M.B. Naegle; 11-18-2020 at 03:15 PM.

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    yep. at zero pressure the belt should be on the driven pulley (the spring in the cylinder or an external spring should have the belt mechanism pulley to that side). Should be simple and reliable. I would possibly have a lever with a catch on the belt shift fork so you can turn the compressor "off" by manually latching the belt over there.

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    For reference, this is the style of valve I'm ordering:
    Gas Air Compressor Pilot Unloader Check Valve Combo 95 - 125 PSI 3/4" X 1/2" 685650074085 | eBay

    It looks like the main variables are the unload pressure, and the connection fittings. 95-125lbs. works for my generic uses, and I take it to mean that the valve will open somewhere within that range (not certain if it's adjustable?), and the valve will be closed at any pressure under the range. This one vents to the atmosphere, which is fine, but I'll probably put an elbow behind the vent since the compressor head will be at chest or head level once it's on a vertical tank and I don't want to blast anyone in the face. I can get smaller/cheaper valves that will likely work fine for this project, but I opted for the 3/4" inlet size as that's what the compressor head measures and I like to avoid adapters where possible.

    How fast do these valves move? If it's more-or-less "instant", I'd like to add an adjustable regulator on the other side of the valve to fine tune the cylinder motion. If it's more of a gradual opening, then perhaps I'm better off with a direct connection.

    Do you think the built in pop-off valve in this combo-assembly is enough, or should I still keep a safety valve on the tank?

    My compressor is also missing the air intake filter. I can always get a modern one, but I found an old intake breather from a hit-n-miss washing machine motor that I think would look better.

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    Why shift the belt ?

    Those controls without the cylinder simply open a port upstream of the tank check valve,
    and let the compressor pump with no resistance.

    Much easier & simpler system.

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    Quote Originally Posted by digger doug View Post
    Why shift the belt ?

    Those controls without the cylinder simply open a port upstream of the tank check valve,
    and let the compressor pump with no resistance.

    Much easier & simpler system.
    True, but then the compressor head will be running(/wearing) continuously so long as the shop and overhead shafting is active. My current compressor use is much more on-demand than continuous.

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    Quote Originally Posted by M.B. Naegle View Post
    For reference, this is the style of valve I'm ordering:
    Gas Air Compressor Pilot Unloader Check Valve Combo 95 - 125 PSI 3/4" X 1/2" 685650074085 | eBay

    It looks like the main variables are the unload pressure, and the connection fittings. 95-125lbs. works for my generic uses, and I take it to mean that the valve will open somewhere within that range (not certain if it's adjustable?), and the valve will be closed at any pressure under the range. This one vents to the atmosphere, which is fine, but I'll probably put an elbow behind the vent since the compressor head will be at chest or head level once it's on a vertical tank and I don't want to blast anyone in the face. I can get smaller/cheaper valves that will likely work fine for this project, but I opted for the 3/4" inlet size as that's what the compressor head measures and I like to avoid adapters where possible.

    How fast do these valves move? If it's more-or-less "instant", I'd like to add an adjustable regulator on the other side of the valve to fine tune the cylinder motion. If it's more of a gradual opening, then perhaps I'm better off with a direct connection.

    Do you think the built in pop-off valve in this combo-assembly is enough, or should I still keep a safety valve on the tank?

    My compressor is also missing the air intake filter. I can always get a modern one, but I found an old intake breather from a hit-n-miss washing machine motor that I think would look better.
    Yes they are instant. All you need inline is a small valve, maybe even a aquarium valve to throttle the cylinder action. Yes to a safety valve as unloaders sometimes stick. Not sure how big your pump is, but if you want a super quiet intake filter/silencer find an old oil bath air cleaner from a tractor. If you don't have intake unloaders for continous running you can keep the oil in it and use that as filtering, mine I have to run empty and use a paper filter on top instead of the cool curved rain cap.001.jpg

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