Key points of selection of common hydraulic valves
The selection of proper hydraulic valve is an important condition to make the design of hydraulic system reasonable, the technical and economic performance excellent, the installation and maintenance simple, and to ensure the normal operation of the system. Because the selection of hydraulic valve is very important to the success of the system, it must be taken seriously.
General principles of type selection
① According to the drag and control function requirements of the system, the function and variety of the hydraulic valve are reasonably selected, and a complete hydraulic circuit and system schematic diagram are formed together with the hydraulic pump, actuator and hydraulic accessories.
② The existing standard shaped series products are preferred, unless it is necessary to design the special hydraulic control valve.
③ According to the working pressure and flow (working flow) of the system, and considering the type of valve, installation and connection mode, operation mode, working medium, size and quality, working life, economy, adaptability and maintenance convenience, source of goods and product history, it is selected from relevant design manuals or product samples.
Type selection of hydraulic valve
The performance requirements of hydraulic system are different, so are the performance requirements of the selected hydraulic valves, and many performances are affected by the structural characteristics. For example, for the system with fast reversing speed, AC electromagnetic reversing valve is generally selected; On the contrary, for the system with slow commutation speed, DC electromagnetic directional valve can be selected; For example, in the hydraulic system, the requirements for valve core reset and neutral energy are particularly strict, and the medium-sized hydraulic structure can be selected; If the hydraulic control check valve is used, and the back pressure of reverse oil outlet is high, but the control pressure cannot be raised very high, the leakage type or pilot type structure should be selected; For the pressure valve to protect the safety of the system, it is required to be sensitive and the pressure overshoot is small, so as to avoid the large impact pressure and absorb the impact of the reversing valve, so the components that can meet the above performance requirements must be selected; If the general flow valve can not meet the accuracy requirements of actuator movement due to the change of pressure or temperature, the speed control valve with pressure compensation device or temperature compensation device should be selected
Selection of nominal pressure and rated flow
(1) Selection of nominal pressure (rated pressure)
The hydraulic valve of 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 properly lower than the nominal pressure value indicated on the product. High pressure series of hydraulic valves are generally applicable to all working pressure ranges below the rated pressure. However, some technical indexes of high-pressure hydraulic components under rated pressure will be different under different working pressure, and some indexes 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 and some performance indexes of the product.
(2) Selection of rated flow
The rated flow of each hydraulic control valve should be close to its working flow, which is the most economical and reasonable match. The valve can also be used under the condition of short-term over flow, but if the valve works under the condition of long-term working flow greater than the rated flow, it is easy to cause hydraulic clamping and hydrodynamic force, and have adverse effects on the working quality of the valve.
In a hydraulic system, the flow of each oil circuit can not be the same, so the flow parameters of the valve can not be selected simply according to the maximum output flow of the hydraulic source, but should consider the maximum flow of each valve in all design states of the hydraulic system, for example, the flow of each oil circuit in series is equal; The flow of parallel oil circuit working at the same time is equal to the sum of the flow of each oil circuit; For the directional valve of differential hydraulic cylinder, its flow selection should take into account that when the hydraulic cylinder changes direction, the flow discharged from the non rod chamber is much larger than that discharged from the rod chamber, and may even be larger than the maximum flow output from the hydraulic pump; For the sequence valve and pressure reducing valve in the system, the working flow should not be far less than the rated flow, otherwise it is easy to produce vibration or other instability; For throttle valve and governor valve, the minimum steady flow should be paid attention to.
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