Dayton Speedaire 3Z784 compressor won't fill beyond 30 PSI

by Paul Morley
(Denton Tx USA)

Dayton Speedaire 3Z784

Dayton Speedaire 3Z784

Dayton Speedaire 3Z784

Dayton Speedaire 3Z784
Dayton Speedaire 3Z784

This Speedaire is new to me but older (not sure how old). The Dayton motor is a 2HP 9K457A single phase. see pics. It runs smoothly but will only fill to about 30 psi. There are no noticeable leaking sounds after I turn it off. I'm really hoping I can replace the gaskets on the 2 cylinders.

Does anyone have any info on this model or what the equivalent model would be. I can't find any references to this one on Grainger's site or any other on google.

There is one more number on the plate on the compressor pump body that says "When ordering parts give this number - 35089"

Any info would be greatly appreciated.

Comments for Dayton Speedaire 3Z784 compressor won't fill beyond 30 PSI

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Mar 18, 2018
Amazing indeed. Help from a compressor manufacturer.
by: Doug in

Looking pretty good now.

Good luck with the gaskets - are they not available or are you just giving it a shot for kicks?

Mar 17, 2018
New details from grainger about 3Z784
by: paul morley

So grainger got back to me with a schematic and parts list. Amazing. Turns out that even though the compressor was manufactured by Florida Pneumatic, the pump was made by Champion and parts are still available for it.

At this point, i'm going to try my hand at making the gaskets for the valve plate and head. I've cleaned up the pistons and the valve plates and heads and other than some fairly bad pitting in one of the valve plates, everything else looks good. None of the reeds are broken/bent so I may be in luck. I'll post more pics and results in the same album.

Mar 15, 2018
re: update Dayton Speedaire 3Z784
by: Doug in

That's pretty ugly.

In the sixth to the last pic, the gasket is broken, and it looks like it was blown before you lifted it.

Looks like it mostly will clean up nicely, and if you can't buy, you can always make gaskets.

Thanks for the update - keep 'em coming!

Mar 14, 2018
by: Paul Morley

The motor runs fine. It doesn't bog down. I don't believe it's a pressure cutoff problem as it won't ever pressurize beyond about 30 psi. IE, the motor keeps running. At this point, i believe it's a valve problem. I've taken the cylinder heads off and have exposed VERY dirty valve plates and piston heads. See pics here.

I've contacted grainger (2nd level tech support) and they said this model was manufactured by a company called Florida Pneumatic which got out of the compressor business in the 90's. They're not optimistic about finding parts for it any longer but are doing an investigation and will get back to me.

Any comments or thoughts? Thank you

Mar 13, 2018
Dayton Speedaire 3Z784 won't fill...
by: Mark

Paul , if the tank is not filling to more than 30psi its more than likely the pressure switch that's the problem.

It might be that the switch has been set to switch off the compressor at 30psi or it might be sticking.

If you take the cover off the switch there should be a screw with a + and - symbol turn the screw one full turn to the + symbol and turn the compressor on it should now fill to more than 30psi, If it still fills to only 30psi get a new pressure switch they are very cheap.

You will need to find out what the correct shut off pressure should be, it will be on the compressor somewhere and adjust the pressure switch to the correct pressure with the screw.

Mar 13, 2018
What happens at 30 PSI?
by: Doug in

Does it bog down at all?

Did you check belt tension?

Is there pressure in the crankcase?

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