Selection points of common hydraulic valves

Choosing the right hydraulic valve is an important condition to make the hydraulic system reasonable in design, excellent in technical and economic performance, easy to install and maintain, and to ensure the normal operation of the system. Because the selection of hydraulic valve is correct or not, it has a great relationship with the success or failure of the system, so it must be taken seriously.

General principles of selection

1. According to the requirements of the driving and control functions of the system, reasonably select the function and variety of the hydraulic valve, and form a complete hydraulic circuit and system schematic diagram together with the hydraulic pump, actuator and hydraulic accessories.

2. The existing standard series products are preferred, and special hydraulic control valves are designed by themselves unless necessary.

3. According to the system working pressure and through flow (working flow) and consider the type of valve, installation and connection method, operation method, working medium, size and quality, working life, economy, adaptability and maintenance convenience, supply and product history etc. are selected from relevant design manuals or product samples.

Type selection of hydraulic valve

The performance requirements of the hydraulic system are different, and the performance requirements of the selected hydraulic valve are also different, and many performances are affected by the structural characteristics. For example, for a system that requires fast reversing speed, an AC electromagnetic reversing valve is generally selected; on the contrary, for a system that requires a slow reversing speed, a DC electromagnetic reversing valve can be selected; for example, in the hydraulic system, the spool reset and centering performance If the requirements are particularly strict, the hydraulic centering structure can be selected; if a hydraulically controlled check valve is used, and the back pressure of the reverse oil outlet is high, but the control pressure cannot be raised very high, the external leakage type or pilot type should be selected. Structure: For the pressure valve to protect the safety of the system, it is required to have a sensitive response, a small pressure overshoot, to avoid large impact pressure, and to absorb the impact generated when the reversing valve is reversed, so it is necessary to select components that can meet the above performance requirements. ;If the general flow valve cannot meet the accuracy requirements of the actuator movement due to changes in pressure or temperature, a speed regulating valve with a pressure compensation device or a temperature compensation device should be selected

Selection of Nominal Pressure and Rated Flow

(1) Selection of nominal pressure (rated pressure)

The hydraulic valve of the corresponding pressure level can be selected according to the working pressure determined in the system design, and the working pressure of the system should be appropriately lower than the nominal pressure value indicated on the product. The hydraulic valves of the high pressure series are generally applicable to all working pressure ranges below the rated pressure. However, some technical indicators formulated for high-pressure hydraulic components under rated pressure conditions will be somewhat different under different working pressures, and some indicators will become better. If the actual working pressure of the hydraulic system is slightly higher than the rated pressure value indicated by the hydraulic valve in a short period of time, it is generally allowed. But it is not allowed to work in this state for a long time, otherwise it will affect the normal life of the product and some performance indicators.

(2) Selection of rated flow

The rated flow of each hydraulic control valve should generally be close to its working flow, which is the most economical and reasonable match. It is also possible to use the valve in a short-term over-flow state, but if the valve works with a working flow greater than the rated flow for a long time, it is easy to cause hydraulic clamping and hydraulic power and adversely affect the working quality of the valve.

The flow of each oil circuit in a hydraulic system cannot be the same, so the flow parameters of the valve cannot be selected simply according to the maximum output flow of the hydraulic source, but the possible flow of each valve through the hydraulic system under all design states should be considered. The maximum flow rate, for example, the flow rate of the series oil circuit is equal; the flow rate of the parallel oil circuit working at the same time is equal to the sum of the flow rates of each oil circuit; for the reversing valve of the differential hydraulic cylinder, the flow selection should take into account the reversing action of the hydraulic cylinder. , The flow rate discharged from the rodless cavity is much larger than that of the rod cavity, and may even be larger than the maximum flow output by the hydraulic pump; for the sequence valve and pressure reducing valve in the system, the working flow should not be much smaller than the rated flow. Otherwise, vibration or other unstable phenomena will easily occur; for throttle valves and speed control valves, attention should be paid to the minimum stable flow.

Post time: May-30-2022