The difference between balancing valve and two-way hydraulic lock
2024-02-06Overview
Bi-directional hydraulic locks and balancing valves can be used as locking components in certain situations to ensure that the working device will not slide, overspeed or move due to external reasons such as its own weight.
However, under some specific speed load conditions, they cannot be used interchangeably. Let’s talk about some of the author’s views on the structural forms of the two products.
The two-way hydraulic lock is the No. 2 component on the right of two hydraulically controlled one-way valves used together (see Figure 1). It is usually used in load-bearing hydraulic cylinders or motor oil circuits to prevent the hydraulic cylinder or motor from sliding down under the action of heavy objects. When action is required, oil must be supplied to another circuit, and the one-way valve must be opened through the internal control oil circuit to allow the oil circuit to Only when it is connected can the hydraulic cylinder or motor operate.
Due to the mechanical structure itself, during the movement of the hydraulic cylinder, the dead weight of the load often causes an instantaneous loss of pressure in the main working chamber, resulting in a vacuum. This situation often occurs on the following common machines:
A vertically placed cylinder in a four-column hydraulic press;
Upper mold cylinder of brick making machinery;
The oil cylinder that swings back and forth in the glass machinery;
Swing cylinder of construction machinery;
winch motor for hydraulic crane;
The more commonly used hydraulic lock is the stacked check valve. Let's look at its cross-section and a typical application.
When the weight falls by its own weight, if the control oil side is not replenished in time, a vacuum will be generated on the B side, causing the control piston to retract under the action of the spring, which will close the one-way valve, and then continue to supply oil, making the working chamber The pressure rises and then opens the one-way valve. Such frequent opening and closing actions will cause the load to advance intermittently during the falling process, resulting in greater impact and vibration. Therefore, two-way hydraulic locks are usually not recommended for high-speed and heavy-load conditions, but are commonly used. It is suitable for closed loops with long support time and low movement speed.
In addition, if you want to solve this problem, you can add a throttle valve on the oil return side to control the falling speed so that the flow rate of the oil pump can fully meet the pressure needs of the control oil.
Structural features of balancing valve:
Counterbalance valve, also called speed limit lock (see Figure 3), is an externally controlled and internally leaking one-way sequence valve. It consists of a one-way valve and a sequence valve used together. In the hydraulic circuit, it can block the hydraulic cylinder or motor. The oil in the oil circuit causes the hydraulic cylinder to
1-end cover; 2, 6, 7-spring seat; 3, 4, 8, 21-spring;
5, 9, 13, 16, 17, 20 - sealing ring 10 - poppet valve; 11 - valve core;
- 14-valve sleeve; 15-control piston; 18-control port cover 19-head;
22-One-way valve core; 23-Valve body
Figure 3 Structural diagram of balancing valve
Or the motor will not slide down due to the weight of the load, and it will act as a lock at this time. When the hydraulic cylinder or motor needs to move, fluid is passed to another oil circuit, and at the same time, the internal oil circuit of the balance valve controls the opening of the sequence valve to connect the circuit and realize its movement. Since the structure of the sequence valve itself is different from that of the two-way hydraulic lock, a certain back pressure is generally established in the working circuit when working, so that the main work of the hydraulic cylinder or motor will not generate negative pressure due to its own weight and overspeed sliding, so no forward movement will occur. Shock and vibration like a two-way hydraulic lock.
Therefore, balance valves are generally used in circuits with high speed and heavy load and certain requirements for speed stability.
Figure 3 is a counterbalance valve with a plate structure, and below is a cross-sectional view of a plug-in counterbalance valve.
Conclusion
Combining the structural analysis of the balance valve and the two-way hydraulic lock, the author recommends:
In the case of low speed and light load with low requirements on speed stability, in order to reduce costs, a two-way hydraulic lock can be used as a circuit lock. However, in cases of high speed and heavy load, especially where high speed stability requirements are required, a two-way hydraulic lock must be used. When using a balance valve as a locking component, you must not blindly pursue cost reduction and choose a two-way hydraulic lock, otherwise it will cause greater losses.
