Working principle of Counterbalance Valves

In order to improve the balance valve's shortcomings of heavy-load low-frequency vibration and reciprocating stall and overspeed in actual projects, this article introduces the Counterbalance valve, analyzes its working principle from the perspective of dynamic balance and hydraulic lock functions, lists specific engineering examples, and provides two-way balance valves. The application and development of balancing valves provide a certain reference.

introduction

Engineering machinery has complex working conditions. In its hydraulic transmission system, in order to avoid stalling or overspeeding, balance valves are often used to solve this problem. However, low-frequency vibration will occur when the load is heavy, and it cannot solve the problem of reciprocating or rotating motion. stalling and overspeeding issues. Therefore, this article introduces a two-way balancing valve to improve the shortcomings of the balancing valve.
1. Working principle of Counterbalance valve
The Counterbalance valve is composed of a pair of identical balancing valves connected in parallel. The graphic symbol is as shown in Figure 1. The control oil port is connected to the oil inlet of the branch on the other side. The Counterbalance valve is composed of a main valve core and a one-way valve sleeve, a main valve core spring and a one-way valve spring. The throttling control port is composed of the balance valve main valve core and the one-way valve sleeve.

The Counterbalance valve mainly has two functions: hydraulic lock function and dynamic balancing function. The working principle of these two functions is mainly analyzed.

Dynamic balance function:

Assuming that pressure oil flows from C1 to the actuator, the pressure oil overcomes the spring force of the one-way valve in this branch, causing the throttle valve control port to open, and the pressure oil flows into the actuator. The return oil acts on the main valve core of this branch from C2, and together with the pressure oil in the control port, drives the movement of the main valve core. Due to the force of the main valve core spring, the oil return chamber of the actuator has back pressure, thereby ensuring smooth movement of the actuator. When the pressure oil flows from C2 into the actuator, the Check Valve at C2 and the main valve core at C1 act, which is the same as the above working principle.

Hydraulic lock function:

When there is no pressure oil at V1 and V2, the oil pressure at the control port of the two-way balance valve is very small, almost 0MPa, and the oil pressure in the actuator cannot overcome the spring force of the main valve core, so the main valve core cannot If the valve moves, and the one-way valve cannot conduct, the throttle control port is in a closed state, and the two chambers of the actuator are locked and can stay in any position.

Through the above analysis, the Counterbalance valve not only makes the hydraulic actuator move smoothly, but also has the performance of hydraulic lock, so it is widely used. This article mainly introduces specific engineering examples of heavy load and reciprocating motion.

The application of the hydraulic principle in the main girder legs of the high-speed railway bridge erecting machine is shown in Figure 2. The main girder legs of the high-speed railway bridge erecting machine are at rest. It not only supports the weight of the bridge erecting machine itself, but also includes the weight of the concrete beams. The load is large and the support time is long. At this time, the hydraulic locking function of the two-way balance valve is used. When the bridge erecting machine moves up and down, due to its heavy weight, it needs to move smoothly. At this time, the dynamic balance of the two-way balance valve is used. There is also a One-Way Throttle Valve in the system, which increases the back pressure of the actuator and further improves the movement. stability.

In the application of aerial work platform booms, the hydraulic schematic diagram is shown in Figure 3. When the luffing angle of the boom increases or decreases, the movement is required to be smooth, and the two-way balance valve prevents stalling or overspeeding during its reciprocating motion, thus avoiding certain dangers.