Working principle of superimposed relief valve

The superimposed relief valve is a hydraulic control element that integrates the overflow function and modular design characteristics. It is widely used in hydraulic systems to achieve pressure regulation, overload protection and system pressure stabilization. Its working principle combines the core mechanism of the pilot relief valve with the compact structural advantages of the superimposed valve. The following details are explained in detail from four aspects: structural composition, working process, characteristic analysis and typical applications:

1. Structural composition: modular layered design

The superimposed relief valve is made up of multiple functional modules superimposed by bolts, each module undertakes a specific function, and a typical structure includes:

Main valve module:

Main valve core: conical or spherical structure, which cooperates with the valve seat to control the main oil passage opening and breakage.

Spring chamber: Built-in pressure regulating spring to provide the preload force required for the main valve core to close.

Pilot valve module:

Pilot valve core: small conical valve, controlling the pressure of the pilot oil circuit.

Pressure regulating screw: Change the compression amount of the pilot spring by rotation to set the system pressure.

Superimposed base plate:

Provides standard installation interfaces (such as ISO 4401 standard) and can be connected in series with other superimposed valves (such as directional valves, pressure reducing valves) to simplify pipeline connections.

Advantages: Modular design reduces installation space, reduces leakage risk, and facilitates system expansion and maintenance.

2. Working principle: Two-level pressure control mechanism

The superimposed relief valve realizes pressure regulation through the linkage between the pilot valve and the main valve. The working process is divided into two stages: steady-state operation and dynamic response:

1. Steady state operation: pressure setting and balance

Pressure setting:

Rotate the pressure regulating screw to compress the pilot spring and set the pilot valve opening pressure (i.e. the system set pressure).

For example: When the pressure regulating screw is rotated to a certain position, the corresponding pressure of the pilot spring preload is 10MPa.

Pressure balance:

When the system pressure is lower than the set value, the pilot valve is closed, the main valve core is close to the valve seat under the action of the pressure regulating spring, the main oil circuit is closed, and all hydraulic oil flows to the actuator (such as hydraulic cylinder).

When the system pressure reaches the set value, the pilot valve core opens against the spring force, the pilot oil circuit is turned on, and the high-pressure oil enters the main valve spring cavity through the damping hole.

2. Dynamic response: overflow voltage stabilization

Main valve open:

The pilot oil circuit pressure acts on the upper end surface of the main valve core and forms a combined force with the main valve spring force.

When the combined force exceeds the hydraulic force on the lower end surface of the main valve core, the main valve core moves upward, the main oil circuit communicates with the return oil chamber, and overflow begins.

Stable pressure:

During the overflow process, the system pressure drops due to oil leakage, and the pilot valve core gradually closes under the action of a spring to reduce the flow of the pilot oil circuit.

The main valve core maintains a slight opening under the dynamic balance of spring force and hydraulic pressure, so that the system pressure is stable near the set value (usually fluctuating ≤±0.5MPa).

Key point: The function of the damping hole is to delay the pressure change of the main valve spring cavity and avoid pressure oscillation caused by frequent opening and closing of the main valve core.