Head Unloader setup of 3Z180

by Lloyd
(Florence KY )

Hello, I recently acquired a SPEEDAIRE Model 3z181 pump to use in my shop. I plan to run it with a 10 hp Dayton that I have and mount on 120 gallon tank.

I am not a pump expert by any means but usually figure out or can find information on what I need but I am perplexed here.

At first sight, this pump would appear to have a centrifugal unloader but in cleaning and getting ready to install it, I discovered that there is no valve mechanism in the housing and the housing has a plug in the fitting, all looks original.

I am sure this is normal but I have not seen it and help would be appreciated.


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May 06, 2016

by: Bill

Lloyd, if you haven't got the manual for your 3Z180, it's here:


Page 4 of the manual provides this information, along with much more:

This compressor is equipped with head
valve unloaders. The pilot valve is
designed to act as an automatic ON and
OFF air switch. When in the ON
position it allows air to flow from the tank
through the valve to the compressor
head unloader mechanism, thus
actuating it. In the OFF position this
valve stops the flow of air through the
valve and releases the pressure in the
line to the head unloader.
The pilot valve works as follows: Tank
air pressure acts on the bottom of the
valve. When pressure is great enough to
overcome spring force holding valve
down on lower seat, it lifts off seat and
allows air to flow around valve and out
through side opening in pilot valve.
When valve lifts off lower seat it moves
up and seats on upper seat where it is
held by tank pressure. When pressure in
tank and on valve drops, spring forces
valve back down on lower seat. Air in
line to device being actuated can then
escape through upper seat and out vent
hole. The pressure at which the pilot
valve is ON or OFF is controlled by the
spring which has been installed at the
factory. A small adjustment can be made
in the field by changing the spring force
by compressing the sp
ring more or less
with the adjusting screw provided on the
pilot valve. "

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