1950's Greiff compressor - no unloading/checkvalve?

by Bengt Nyberg
(Stockholm, Sweden)

1950's Greiff compressor

1950's Greiff compressor

1950's Greiff compressor
1950's Greiff compressor motor


The other day I bought an old 2 cylinder, one stage compressor.
The brand is Greiff (Swedish) and it's belt driven by a 4.5 Hp 3-phase motor, controlled by a Danfoss MP-15 pressure switch via a Y/D-coupler.

At the moment, I only have a couple of - not so good - Pictures for you but I can get plenty more if needed.

The seller told me that the compressor had been running fine till one day when it wouldn't restart again, once there was pressure in the tank.

Both the seller and I figured that there must be a broken check valve somewhere.

My problems are two:
1. I can't find a check valve or unloading mechanism anywhere.
2. I can't find any information on Greiff compressors anywhere.

So, I'm now confused and full of questions.

What I know / have done so far:

- From empty tank, the compressor runs just fine and happily builds up pressure till the pressure switch shuts it off. Once the pressure switch turns the motor on again, it can't get the pump going.

- I've looked through every part between the exhaust port of the pump and the tank and have not found any check valve. (In the Pictures you will see a big piece of iron bolted to the exhaust port. This is the lower half of a very robust cyclone water separator that I have thoroughly inspected to make sure there are no valves in that).

- Turning to the internet for information, I can't find any on this compressor, so now I turn to you.

- Are there head designs that incorporate check valve/unloader?

- If so, is it likely that this is one of them?

- Do you have any information on these compressors?
- Can you Point me in the right direction to find any information on this thing?

More info:
- There is a rigid tube going from the crank case to the air cleaner (almost visible in one of the Pictures). I figure this is just crank case ventilation but have not examined it further.

- I popped one of the caps on the top of the heads. This revealed a very large "slotted screw" (huge slot) - I've found other valve mechanism designs that looks similar - e.g. Devilbiss 330.

- The pressure switch takes it's Control pressure from the tank via a small tube.

If there is any more info on this thing that you would like - just ask!


Comments for 1950's Greiff compressor - no unloading/checkvalve?

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Feb 05, 2015
unloader check valve
by: Doug in s.d.ca

Looks nice.

And yes, some compressors do have the unloader built in. If you're lucky, there's a plate or whatever near the crank for access.

Can't say I know how they work, but I've seen a few pumps that say "with unloader".

Feb 05, 2015
Correction: no Y/D coupler
by: Bengt Nyberg

Just a correction. There is no Y/D coupler, just a 3-phase contactor between the motor and the pressure switch.


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