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Unloader Valves On Twin V Piston Compressor Guide

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This page covers information about twin cylinder reciprocating compressor unloader valves and how they function in this configuration. For a more in depth guide on unloader valves take a look at my guide to air compressor unloader valves.

About unloaders for a twin V compressor.

by chuck
(Rockford ILLINOIS)

I am having no luck figuring this out. Hope you can help.

I bought a new v-twin compressor with head unloaders.

I know what unloaders do but I am faced with two types (I think). Check valve w/unloader port and switch with unloader.

I have both available.

Does the check valve unloader port go to the heads and that’s it?

Do the unloader heads need pressure in the 1/4″ line to unload?

Or is the switch unloader only used to dump the line between the tank check valve and head?

Ideally I would like to be able to switch between continuous run to start/stop mode.

Thanks in advance. Chuck B.


Hello Chuck B.

In every case the unloader is used to dump the air over the piston to ease the compressor start up.

In a two stage compressor air is compressed from one cylinder to the other, pre-compressing it, and allowing the second cylinder to compress it further into the tank.

Both pistons need to be unloaded to allow the compressor easier re-start.

There’s usually a check valve in the line between the pistons, and on the secondary piston side, an unloader to allow that higher pressure piston to unload too.

Something must operate the unloader valves. In a single piston compressor, that unloader valve is usually located in or as part of the pressure switch.

You’ll have to check your manual to see which goes where. I can’t determine it with the info provided.

Additional valve reading:

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By Bill Wade

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