I have a old Speedaire compressor driven by a 1/2 hp electric motor and want to convert to a 2hp briggs and straton gas motor. What do I need to control the compressor on/off cycle other the a adjustable relief valve. I'm retired so cheap is good.
any help would be great!

 

An adjustable relief is about the only way you can do it with a gas engine with no on-off control. I would use two pressure relief valves tho with slightly different settings.

You could make some sort of throttle down setup when it reached pressure with an air cylinder and some pressure controls but unless you had access to that stuff in your junk box it would get $$$.

 

All,
A centrifugal clutch similiar to a go kart clutch would probably be a great place to start. The next idea would be to control the throttle somehow? Your signal to throttle down would have to come from a pressure transducing sensor. this should be adjustable to your specific needs and have some sort of electrical contacts. This should be applicable voltage to whatever your motor is making (i.e. 12VDC?) Use a airconditioning solenoid similiar to those found on most automotive projects to go from idle to wide open throttle (WOT). You may have to rig some sort of lever to get the ratio correct. When the pressure transducer closes due to high pressure the actuating solenoid will retract and bring the motor to idle.
KingFisher
Easier said, than done.

 

The clutch would give an on-off control, -good idea!

-That is why I made the junk box comment. I could probably rig it from my junk box but the average guy would be out of luck. Most of those small engines do not have a source of 12VDC either.

 

All,
Most compressors already have a pressure switch. This would be the device to actuate either a throttle actuator or, possibly, an electric clutch (not go-kart type). My rider mower has a 12VDC system. Most small mowers have a coil which means there is some voltage source. What's the potential? I don't know off hand, but I'd assume its 12VDC?
Consider it,
KingFisher

 

The coil in most small engines is for the magneto ignition, mega volts...

 

Couldn't a small AC to DC inverter be used to get the 12 v? Of course, that means having a 110v cord involved, somewhat defeating the purpose of going to gas.

How do those old, inline gas engined welders control the throttle? I've seen some built back in the '60's that would idle down until you struck an arc....

 

Why reinvent the wheel. You have got to approach this from the correct angle.

So we assume you have no electricity on this machine. What other utility is there? Compressed air of course. So what you need is an unloader valve that works when compressed air is applied and a throttle control actuator to push the throttle to idle when the pressure is high enough. And you need an air governor. It sends pressure down a control line when the main line gets to the cutoff pressure and relieves the control line when the mainline drops. The air governor and unloader valve I imagine you might find on a Mack Midliner or other European truck in a junk yard. The throttle control might be a little trickier but shouldn't be that hard to find at all.

Birken

 

At the compressor store the throttle control isnt bad but the unloader is pricey. Sounds like Birken worked on one or 2. Electric and gas systems opertate totally different. I have a Mack Midliner by the way. I wouldnt mind finding a real service manual if there was one floating around.

 

Contact someone at the California Department of Forestry shop in Davis, they have a ton of Midliners and ought to be able to help you find a manual.

Birken