Physical photo of air-cooled hydraulic pump station for hydraulic press

One feature of the air-cooled hydraulic pump station used in hydraulic presses/hydraulic transmission is that it can easily achieve overload protection, which is achieved by the relief valve. It works by opening the valve port to release pressure, keeping the system pressure constant or limiting the maximum pressure. The following figure shows some common overflow valves.
Overflow valves can not only function as safety valves, but also serve as pressure regulating valves, unloading valves, back pressure valves, balance valves, and other applications. When used as a safety valve in the system, the relief valve is in a normally closed state and only opens when the system is overloaded to limit the maximum pressure of the hydraulic system and protect the hydraulic system or mechanical structure; In the throttle valve speed control system, the relief valve is in a normally open state, and at this time, the relief valve is a pressure regulating valve or a constant pressure valve to maintain a constant pressure in the system.

According to different structures, relief valves are divided into two types: direct acting and pilot operated. The combination of a pilot operated relief valve and an electromagnetic directional valve can form an electromagnetic relief valve, while the combination of a pilot operated relief valve and a one-way valve can form an unloading relief valve. Below are separate introductions.

1. Direct acting overflow valve

Direct acting relief valves have three structures: cone valve, ball valve, and slide valve. The following figure shows the working principle of a direct acting relief valve with a slide valve structure.
Pressure oil enters the bottom of the valve core through the damping hole. When the force acting on the valve core is greater than the spring force, the valve port opens, allowing the oil to overflow. By turning the handwheel, the spring preload can be adjusted to regulate the opening pressure of the relief valve. By replacing springs with different stiffness, the pressure regulating range of the relief valve can be adjusted. The direct acting overflow valve has a simple structure and high sensitivity, but it is not suitable for high-pressure and high flow situations. The following figure is a cross-sectional view of the Rexroth DBD relief valve, with the same principle as the above figure. Please refer to the Rexroth sample for details. Physical photo of air-cooled hydraulic pump station for hydraulic press