Pressure relief valve

Through this page, I try to make a short description about pressure relief valve types although the subject is familiar. If google it sure it will find some good information about it.
Even though the subject is frequent meet it will be show more deeply information from source, where I learn and understand this hydraulic component.
I will present information about one of the common pressure control valves namely pressure relief valve.
It is a normally close valve and its function is to limit the pressure to a specific maximum value by diverting the pump flow back to the tank. I say maximum value because if the system working pressure is 1300 psi (90 bar), the pressure limiting valve should open 1375 psi (95). The valve passage should be as big as the maximum pump output.
In practice a pressure relief valve types you’ll come across the terms overflow valve, pressure regulating valve, safety valve.
Relief valve operation in open circuit diagram
The valve should not be used to direct excess pressure to the tank, as this may cause the system to overheat as shown in the hydraulic open circuit diagram

In system diagram shown all the excess oil is pumped at a pressure set of let’s say 1375 psi (95 bar) through the relief valve back to the tank. Therefore, result of this is enormous heat generation in the pressure limiting valve. In this case the 4/2 valve manually operated with spring return will be replaced by a 4/3 valve. When this valve is center the oil will circulate without pressure thorough the valve.
- It provides protection against any actuators overloads in the hydraulic system;
- It’s a normally closed valve and also limit the pressure to a specified maximum value;
- In practice a relief valve is also find under the terms of overflow valve, pressure regulating valve, safety valve.
[…] Pressure limiting valves in a hydraulic system opens when pressure set is reach or when pressure in the system increase over value set. This prevents the pressure in the system to become excessive. […]