I have a very old compressor (areograph) that I’m trying to restore. It has no check valve and the main compressed air outlet from the pump goes straight into the tank. There are a couple of small pipes coming off the piston head, looks like on top of the inlet valve side of the pistons, they are broken off and do not connect anywhere. From old photos on the internet of similar compressors, it looks like these used to connect into the tank too via a separate connection. In which case I don’t understand what they’re for, and also how pressure from the cylinders is released when the motor stops...? Looks like this is designed to add pressure to the cylinder head (on the inlet side) rather than take it away? Can anyone advise?
- Thread starter simpjd
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the snooper
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It should have four valves in the head so you will need to remove the big nuts on the head, probably have disc valves in there, the pressure in the delivery pipe is released via the on off switch when it reaches pressure, they're not fitted to the pump
Thanks! I assume the 2 big nuts on the side where the big outlet pipes (delivery pipes) into the tank are, are the outlet valves (agree probably disc/diaphragm valves). This is presumably where the pressure needs to be released from. However, there is no check value on the outlet/delivery pipe (goes straight into tank) and it looks pretty original and untouched! This makes me think these old compressors work a different way.... (see link below which makes me think this).
https://www.mig-welding.co.uk/forum/threads/does-this-old-compressor-need-an-unloader-valve.91253/
I think this also due to the fact that there is a small pipe coming off the other side of the head, presumably the inlet side....what is this little pipe for! It still links the two cylinders together on the inlet side, however has an empty thread showing it also used to go somewhere else after linking the two cylinders....
https://www.mig-welding.co.uk/forum/threads/does-this-old-compressor-need-an-unloader-valve.91253/
I think this also due to the fact that there is a small pipe coming off the other side of the head, presumably the inlet side....what is this little pipe for! It still links the two cylinders together on the inlet side, however has an empty thread showing it also used to go somewhere else after linking the two cylinders....
the snooper
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The delivery pipe would go to a non return valve on the receiver which is where the pressure release pipe would also connected and go back to the pressure switch which vents the delivery when pressure is reached, the pumps don't have a valve to vent the delivery pipe, as it would be a headache having to get it exactly set to the on off pressure switch
Yeah, agree this is how a modern compressor would work. However I "think" this old compressor works differently. This is because:
1. no non return value on the delivery pipe (possible this could have been removed, however pipes look pretty untouched to me)
2. the small pipe linking the two cylinder heads on the inlet side (rather than the outlet/delivery side), which also used to connect to somewhere else (direct to the receiver via a value?), however this pipe has been removed.....
Surely if it worked the same as a modern compressor, the small pipe would be on the delivery/outlet side? Or is the small pipe which used to connect to somewhere else for something else?
The links I posted above are interesting and are what is making me think this old compressor might be different....
If you pressurised the inlet side to the same as the outlet side, would the pistons just free spin with no load under a balanced pressure on both sides? Maybe this is an old way of regulating pressure in the tank? However if so wouldn't the pressure to the inlet inlet side just escape?
...or am I just completely misunderstanding this?!
1. no non return value on the delivery pipe (possible this could have been removed, however pipes look pretty untouched to me)
2. the small pipe linking the two cylinder heads on the inlet side (rather than the outlet/delivery side), which also used to connect to somewhere else (direct to the receiver via a value?), however this pipe has been removed.....
Surely if it worked the same as a modern compressor, the small pipe would be on the delivery/outlet side? Or is the small pipe which used to connect to somewhere else for something else?
The links I posted above are interesting and are what is making me think this old compressor might be different....
If you pressurised the inlet side to the same as the outlet side, would the pistons just free spin with no load under a balanced pressure on both sides? Maybe this is an old way of regulating pressure in the tank? However if so wouldn't the pressure to the inlet inlet side just escape?
...or am I just completely misunderstanding this?!
the snooper
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You wouldn't want a nrv on the delivery pipe near to the pump otherwise the delivery pipe would have constant pressure in it and no room for the pump to get upto speed before building pressure, the small pipes probably went to the unloader valve
brightspark
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this is the sort of pressure switch that would have been fitted only this is a modern version. it fits in the air tank and a small pipe goes from it to the top of the valves . the motor would run permanently and filled the tank with air when up to pressure set by the switch it would open and decompress the inlet valves stopping the air compressing when pressure drops it closes letting the inlet valves suck in air . now u would just fit an electrical one and stop and start the motor https://www.zoro.com/westward-unloading-valve-pn2407017g/i/G8303145/
Thanks brightspark, this is really interesting. Apologies for the basic questions, however still trying to 100% get my head around this:
So it looks like my compressor was originally designed for continuous motor operation.
1. So the "pressure switch" on these old compressors would have its own connection to the air tank (not connect through the main outlet/delivery pipe)?
2. The pressure switch allows the motor run continuously, simply because its venting back out of the air tank, as well as decompressing the inlet side of the piston?
3. Does decompressing the inlet side of the piston mean that the pistons and motor continue running with no load? If you decompress the inlet side, does it not also decompress the outlet?
Many thanks!
brightspark
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the 2 inlet valves normaly open and close and suck in air then compress it. the unloader valve is set to required pressure and normaly closed. its fed of the main tank . when up to pressure it opens and the air pressure in the small outlet pipe operates the 2 decompressors on the top of the valves a small rod presses the valves open stopping them from operating when pressure drops the small pipe empties and the decompressors retract and alow the valves to work compressing the air it only decompresses the inlets as the outlet valves will stay shut holding the air in the tank . modern comps use a none return valve on the tank which takes the pressure of the valves and when used with a modern switch empties the pipe of air when up to pressure .when air drops in pressure the motor cuts in the pipe fills and away it goes it gives the motor chance to build up speed before compressing the air. other members may explain it better or add to it 
