As we all know, most of the failures of the hydraulic system are caused by oil pollution, so the filter plays an important role in the hydraulic system. As a hydraulic designer, choosing a filter is sometimes a headache. Because, no matter what brand of filter, there are many kinds, and the various parameters and curves on the sample are confusing. Today, Xiaobian share a little experience in the selection of filters.
Let's figure out where you need a filter in your hydraulic system.
l pump outlet high pressure filter
l Bypass filter
l Special filter for key parts
picture
The above filters are not necessarily used at the same time, and different industries may choose different options.
Oil suction filter: Generally a very low precision filter, can directly protect the pump. In general, unless the oil accuracy management is poor, it will be used, because, normally, the oil in the protective tank with the return Oil Filter will never have too much impurities, unless the tank is open. Oil suction filter is not recommended now, because it has a great impact on the suction of the pump, and it is completely unnecessary.
Pump outlet high pressure filter: High pressure is a major feature, here the filter must be resistant to high pressure, and should be higher than the system pressure a grade. The oil pumped out is directly into each control valve, so the cleanliness of the oil must be able to ensure the needs of the system, so the filter here is very important.
Oil Return Filter: oil cylinder, motor, valve, etc. will produce wear impurities in the work, as well as maintenance, pipeline reconnection and other external impurities. The return oil filter is to filter out these impurities. It is characterized by low pressure, large flow and low filtration accuracy.
Bypass filter: Independent filtration system, specially used for cleaning or cooling oil. Generally, the filtration accuracy is relatively high.
Special filter for key parts: Generally, the filter is added separately before the valve or actuator with higher cleanliness requirements, and the accuracy is higher.
Filter selection procedure
1. First determine the filter form and pressure level according to the use position.
Use location
Pump outlet
Oil return
by-pass
Key position
Pressure rating
1.5 times the working pressure
1.6MPa, 2.5MPa
1.5 times the working pressure
1.5 times the working pressure
type
Pipeline type, side plate, top plate. monocular
Insert type, floor type. Single or double barrel
Insert type, floor type. Single or double barrel
Pipeline type, side plate, top plate. monocular
2. Select the appropriate filtration accuracy according to the cleanliness required by the system. This depends on the type of filter configured for the specific system.
For example, the cleanliness of the rolling hydraulic system requires NAS6, and the pump outlet + oil return + by-pass filter combination can be selected. Pump outlet 10 microns, oil return 20 microns, bypass 3 microns.
3. Then it is time to select the specific model with the manufacturer's sample.
There are many models of each manufacturer, and the specific choice should refer to the experience of predecessors and the technical support of manufacturers.
Almost every manufacturer will give the pressure difference curve of the filter, which will always make people confused. Here are some lessons to share. picture
When you determine which type of filter to use, then determine the maximum flow rate of the filter in the system, and then find out in the curve how much is the pressure difference of the different specifications of the filter under this flow rate, and then find out the pressure difference of the filter housing, the two sum is the overall maximum pressure difference of the filter.
△P total =△P shell +△P filter element
Of course, there is also a relationship between viscosity, so the real pressure difference should be multiplied by a coefficient, which is the viscosity of the oil used in the system divided by the viscosity of the sample curve.
In what range is this total pressure difference appropriate:
Pump outlet/bypass/Key position filter: △P total ≤1bar;
Others: △P total ≤0.05bar;
4. Some auxiliary functions should be selected according to the specific situation.
Blocking alarm: mechanical visual, light visual, signal remote transmission and so on.
Bypass check valve opening pressure.
