By the end of this lesson, you will be able to explain how unloading valves function.
And list common uses of unloading valves.
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.
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).
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.
Become a member to get immediate access to the rest of this lesson, and all the other great content on LunchBox Sessions.