Core differences between overflow valves, pressure reducing valves, and sequence valves.

Hydraulic valves are components used in hydraulic transmission to control liquid pressure, flow, and direction. Among them, pressure control valves alone can be categorized into several types, such as overflow valves, pressure reducing valves, sequence valves, and unloading valves. This article shares the similarities and differences among three types of pressure valves to help you quickly distinguish them.

1. Overflow Valve
   An overflow valve is a type of hydraulic pressure control valve. In hydraulic equipment, it primarily serves functions such as pressure regulation and overflow, pressure stabilization, system unloading, and safety protection.
2. Pressure Reducing Valve
   A pressure reducing valve reduces the inlet pressure to a required outlet pressure through adjustment. It relies on the energy of the medium itself to automatically maintain a stable outlet pressure.
3. Sequence Valve
   A sequence valve is used in systems with two or more branch circuits to control the action sequence of multiple actuators based on circuit pressure. Depending on its function and assembly structure, it can achieve various circuit functions, such as those of an overflow valve, sequence valve, backpressure valve, unloading valve, or counterbalance valve.

Similarities
As pressure control valves, their working principles are fundamentally the same. They all use the control pressure of the pressure oil to open or close the valve port.

Differences
The pressure reducing valve is mainly used to lower the pressure in a specific branch circuit of a hydraulic system, ensuring that the branch pressure is lower and more stable than the main circuit pressure. Within the set pressure range, the pressure reducing valve remains closed, similar to an overflow valve. However, as the system pressure rises and reaches the set pressure of the pressure reducing valve, it opens, allowing some oil to return to the tank (this raises the oil temperature in the tank as pressurized oil returns). The pressure in this branch circuit will not increase further. The pressure reducing valve provides pressure reduction and stabilization for its branch circuit.

In contrast, the overflow valve is installed at the pump outlet to ensure the overall system pressure remains stable and does not exceed safe limits. It can be said that the overflow valve operates passively, while the pressure reducing valve operates actively.

Slight Differences in the Roles of the Three Valves in Hydraulic Systems

· The overflow valve provides pressure regulation and overflow, stabilization, system unloading, and safety protection.
· The pressure reducing valve provides pressure reduction and stabilization.
· The main functions of the sequence valve include:

1. Controlling the sequential action of multiple components;
2. Used in pressure-holding circuits;
3. Acting as a counterbalance valve to prevent the free fall of a cylinder piston due to its own weight;
4. Using an externally controlled sequence valve as an unloading valve to unload the pump;
5. Using an internally controlled sequence valve as a backpressure valve.

Summary of the Differences Among the Three Valves

1. Controlled Pressure:
   · Pressure reducing valve: Controlled by outlet pressure to ensure a constant outlet pressure.
   · Overflow valve: Controlled by inlet pressure to ensure a constant inlet pressure.
   · Sequence valve: Can be controlled by inlet pressure or external pressure.
2. Valve Port State When Not Operating:
   · Pressure reducing valve: Valve port is normally open.
   · Overflow valve: Valve port is normally closed.
   · Sequence valve: Valve port is normally closed.
3. Valve Port State During Operation:
   · Pressure reducing valve: Valve port narrows.
   · Overflow valve: Valve port opens.
   · Sequence valve: Valve port opens.
4. Oil Drain Port:
   · Pressure reducing valve: Has a separate oil drain port.
   · Sequence valve: Typically has a separate oil drain port.
   · Overflow valve: Leakage oil from the spring chamber is internally drained to the outlet through the valve body flow path.