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Unloading Valves

By the end of this lesson, you will be able to explain how unloading valves function.

And list common uses of unloading valves.

What is It?

Unloading valves are very similar to balanced, pilot-operated relief valves. The only difference is where the pilot pressure comes from.

In unloading valves when external pressure is applied to Port X that is greater than the pilot setting, the pilot poppet will crack open, allowing the main poppet to open. System flow will then unload from Port P to Port T.

Port X
Port P
Port T
Pilot Poppet
Main Poppet

As you can see by comparing the balanced, pilot-operated relief and unloading valve cutaways below, the only difference is the plug in the unloading valve that is blocking Port P from the pilot section. Therefore, the pilot pressure must come from an external source (Port X).

Port P
Port T
Pilot Section
Main Section
Balanced, Pilot-Operated Relief Valve Cutaway
Port X
Port P
Port T
Pilot Section
Main Section
Plug
Unloading Valve Cutaway

Schematic Symbols

Unloading valve symbols are also drawn in a very similar way as some other types of valves.

The function of many pressure valves on a schematic can be clarified by their location within the hydraulic system.

Port X
Port P
Port T
Pilot Section
Main Section
X
P
T
Basic Unloading Valve Symbol
X
P
T
Pilot Section
Main Section
Denison Unloading Valve Symbol

Build It!

Drag and drop the pieces to build the unloading valve. Not all pieces will be used.

This is just a preview!

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We hope you enjoyed Unloading Valves

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