Hydraulic system filter introduction – Manifold blockS


1. Filter definitions – Manifold blockS


The process of removing contaminants from a fluid (liquid or gas) using a porous medium.


When the fluid (liquid or gas) into a certain specification of the filter, the impurities are blocked, and the clean filtrate is discharged from the filter outlet, when the need to clean, as long as the removable filter element is removed, cleaning or replacement after reloading can be, use and maintenance is very convenient.



Filter structure diagram


2. Filter principle – Manifold blockS


Surface filtration


The filtered particulate contaminants are almost all trapped on the upstream side of the filter element surface. The filter element material has uniform calibration holes, which can filter out solid particles larger than the calibration holes. Specific divide into line gap type, net type and piece type.


Deep filter – Manifold blockS


The filter core of the depth filter is porous and permeable material, and the internal channel is tortuous and circuitous. The pollution particles larger than the pore size are directly intercepted on the outer surface near the upstream of the oil, while the smaller particles enter the inner channel of the filter element, deviate from the flow beam due to the action of surface tension (molecular adsorption force, electrostatic force, etc.), and are absorbed on the inner wall of the filter channel. Therefore, the filtering principle of depth filter has both direct interception and adsorption. The filter material includes paper core, sintered metal, felt and various fibers.


Manifold blockS – Adsorption filtration


Mainly refers to the magnetic filter, rely on magnetic material magnetic force to attract iron filings and magnetic abrasive. Filter element is made of permanent magnet, can absorb iron filings in the oil, iron powder or magnetic grinding powder, often made with other forms of filter element compound filter, the scope of application will be limited.


3. Installation position of filter in hydraulic system


The manifold blockS are installed in the pump


Filter is required to have a large flow capacity and small resistance, the flow should be more than twice the pump flow, to prevent cavitation phenomenon. Mainly used to protect the hydraulic pump, but the wear products generated in the hydraulic pump will still enter the system. Generally, a filter with lower filtering accuracy is used.


Manifold blockS are installed at the oil outlet of the pump


The filter should be able to withstand the working pressure and impact pressure on the oil road; In order to prevent the filter blockage caused by hydraulic pump overload or damage to the filter element, the pressure oil road should be parallel side valve or series one indicating device. This method is often used for filtering precision requirements of the system and servo valve and speed control valve, in order to ensure their normal work.


Install on manifold blockS


These are called return oil filters, which remove metal and rubber particles from the worn hydraulic components to protect the cleanliness of the fluid flowing back to the tank. Allow the use of lower strength and stiffness of the filter filter; In order to prevent the system pressure rise caused by the blockage of the filter element, a one-way valve in parallel with the filter is required to act as a bypass valve.


Standalone bypass filter – Manifold blockS


In the hydraulic system of large machinery, independent filtration system composed of hydraulic pump and filter can be specially set up, which can continuously remove impurities in the system and improve the cleanliness of oil. Such as oil filter car.


4. Filter selection steps – Manifold blockS


Clear design requirements: clear system pressure, flow, hydraulic oil grade, working temperature;


Determine the filtration accuracy level required by the system;


According to the filter in the hydraulic circuit installation position and the use of pressure to determine the type of filter;


Determine the size of the specification: pre-select according to experience or pre-selected line chart, and then calculate its initial pressure drop. If the value is greater than the recommended value above, it is necessary to select a filter with a larger flow specification.


Determine the filter pollution signal mode, bypass, etc.


5. Cautions during using – Manifold blockS


Filters should not reverse oil flow, reliable measures should be in place to ensure workers do not misconnect.


After the filter element is polluted, the pressure difference flowing through the filter may open the bypass valve, resulting in incomplete flow filtration of oil, or even collapse of the filter screen. Therefore, the filter must be set up with visual or electrical alarm. Provide accurate and reliable indication as to whether the filter element needs to be replaced. For the filter whose installation position is not convenient for the operator to observe, electric alarm is preferred.


Because the filter element is a wearing part, the design should be set aside to repair the replacement of the filter element space.


Stainless steel filter element can be reused, but considering that the cleanliness of the filter element after cleaning is difficult to reach the standard, it is recommended to choose disposable paper filter element.