Impurities in the hydraulic system usually enter along with the hydraulic oil. The hydraulic suction filter can filter the hydraulic oil before it enters the hydraulic pump, thus preventing the pump and other hydraulic components from being damaged by large particulate pollutants. Now, let me give you a comprehensive introduction to the hydraulic suction filter, so that you can make an appropriate choice.
What is a Hydraulic Suction Filter?
The hydraulic suction filter is a coarse filtration device installed on the suction side of the hydraulic pump. It can filter out large particles of impurities in the hydraulic fluid, such as metal shavings, welding slag, and dust, preventing these impurities from entering the pump body and causing wear on the internal components.
The Function of the Hydraulic Suction Filter
Purify Hydraulic Fluid
As the inlet filter component of the hydraulic system, the hydraulic suction filter can filter out suspended metal debris, rubber wear particles, welding slag and other solid impurities. It can intercept particles with a size ranging from 80 to 250 µm, preventing them from spreading along with the oil circulation.
Maintain the Stability of the System
When contaminants or air enter the suction port of the pump, it will cause the pump to operate unstably or result in cavitation. The hydraulic suction filter adopts a low flow resistance structure to keep a smooth oil flow while filtering.
Extend the Service life of the Equipment
A hydraulic pump is the power source of the hydraulic system. Its internal blades, gears, plungers, and other structures are precise and sensitive to impurities. The hydraulic suction filter can prevent impurities from entering the pump body, avoiding wear and jamming, thereby extending the service life of the hydraulic pump.
At the same time, it can also reduce the occurrence of wear and blockage of hydraulic valve groups, hydraulic cylinders, hydraulic motors and other downstream components. This has extended the lifespan of the entire hydraulic system.
Improve Work Accuracy
Clean oil can make hydraulic valve control more precise and hydraulic actuators more responsive. This avoids system pressure fluctuations, slow actuator actions, or positioning deviations caused by impurity jamming, allowing hydraulic equipment to maintain high-precision operation.
Reduce Operation and Maintenance Costs
By filtering pollutants, hydraulic suction filters can reduce hydraulic system failures caused by pollution. Then, this reduces maintenance time and component replacement costs. At the same time, clean oil can reduce the frictional resistance between hydraulic components and minimize energy loss.
Components of the Hydraulic Suction Filter
Filter Element
The hydraulic suction filter uses a wire mesh as the filter element. The wire mesh has a very low flow resistance coefficient, which allows high viscosity hydraulic oil to pass smoothly at low temperatures. The specifications of this wire mesh are between 60 mesh and 200 mesh.
The wire mesh is usually made of metals such as 304/316 stainless steel or brass, which have strong corrosion resistance. You can clean the wire mesh during maintenance, remove any attached contaminants, and reuse it.
Support Frame
There is a porous metal support frame inside the wire mesh. When the hydraulic pump is operating, a strong vacuum suction force will be generated on the oil suction side. If there is insufficient internal support, the external wire mesh will collapse and deform inward, causing the flow channel to be completely blocked.
This support frame can withstand sufficient negative pressure strength and reduce obstacles when oil passes through, maintaining smooth flow.
End Cap
The upper and lower ends of the wire mesh are sealed and fixed with end caps. The end caps are usually made of glass fiber reinforced nylon or die-cast aluminum alloy. And use industrial-grade epoxy resin to seal and bond the wire mesh with the end cap. If a two-part epoxy is supplied in a dual-cartridge format, a static mixing nozzle can combine the resin and hardener during dispensing.
This allows the hydraulic suction filter to maintain a stable structure even in oil temperature fluctuations ranging from -30 ℃ to 100 ℃.
Connection Interface
There are connectors at both ends of the hydraulic suction filter, which are used to connect the filter to the oil tank and pipeline. The interface is usually in the form of threads or flanges. And at the root of the threads, there is a sealing ring groove or sealing plane to keep a stable installation and prevent oil leakage.
Bypass Valve
The bypass valve is a safety device that prevents pump cavitation and is usually optional. It is integrated at the bottom of the filter element or on the connecting seat, set to low-pressure opening, usually at 2 to 5 psi.
When the filter is severely clogged, the hydraulic pump may experience insufficient oil suction or cavitation. The bypass valve automatically opens when the differential pressure reaches the set value, allowing the oil to flow directly to the pump inlet, so that the pump can continue to suction oil.
How does the Hydraulic Suction Filter Work?
When the hydraulic pump is started, the pressure inside the oil tank will be higher than the pressure at the pump outlet. This pressure difference forces the hydraulic oil to flow from the oil tank to the pump.
Hydraulic oil can pass through the wire mesh. And particles with a diameter larger than the mesh will be blocked outside the filter.
As the intercepted pollutants accumulate on the wire mesh, the resistance of the oil passing through the filter element will increase, resulting in a greater pressure difference between the inside and outside of the filter element. This high resistance will prevent the pump from sucking oil and cause cavitation.
When the pressure difference reaches the set value, the bypass valve will open and the oil can directly enter the hydraulic pump.
Types of Hydraulic Suction Filters
Internal Suction Filter
The internal suction filter is installed on the suction pipeline inside the oil tank, and the filter element is submerged below the oil. The submerged installation can minimize air infiltration into the oil circuit and keep the stability of the oil supply.
However, when the filter needs to be cleaned, you need to drain the hydraulic oil in the tank below the installation height of the filter before maintenance.
The internal suction filter has a lower cost and does not occupy space outside the oil tank. It is suitable for working conditions where the oil suction port needs to be tightly integrated with the oil tank and the external installation space is limited, such as fixed industrial hydraulic equipment and machine tool hydraulic systems.
External Suction Filter
The external suction filter is installed on the suction pipeline outside the hydraulic oil tank. It is rigidly connected to the suction pipeline through flanges, threads or quick connect fittings.
The advantage of an external suction filter is that it is easy to maintain. You don’t need to open the fuel tank access cover. You can directly remove the filter end cap to clean or replace the filter element, which greatly reduces maintenance downtime.
Meanwhile, the size of the external suction filter is not limited by the internal space of the fuel tank. You can choose a model with a larger sewage capacity according to your needs. And you can also equip auxiliary devices such as blockage status indicators.
The external suction filters are widely used in hydraulic systems of various scales. It is also very suitable for high-pollution conditions such as hydraulic systems in mines and hydraulic circuits of large metallurgical equipment.
Spin-On Suction Filter
The spin-on suction filter is fixed to the oil suction port through a threaded interface. Its installation and disassembly are very convenient. You can simply replace the filter element by rotating it.
The spin-on suction filter is compact in size and structure, with very low requirements for installation space. It is suitable for mobile hydraulic equipment such as excavators, loaders, agricultural machinery, and small hydraulic tools.
How to Choose a Hydraulic Suction Filter？
Understand the Flow and Pressure of the System
The flow rate of the hydraulic suction filter must be greater than the maximum working flow rate of the hydraulic pump. It is recommended that you select a hydraulic suction filter with a rated flow rate about 1.5 times the actual flow rate of the pump.
This is because the flow resistance of the hydraulic suction filter will increase as the flow rate increases. If the flow rate is insufficient, it will lead to excessive oil suction resistance of the pump body, causing cavitation.
At the same time, the housing and internal structure of the hydraulic suction filter should be able to withstand the actual pressure peak on the suction side.
Determine the Filtration Accuracy
The key component of the hydraulic suction filter is the filter element. Its aperture determines the range of pollutant particle sizes that can be blocked. Usually, the filtration accuracy of hydraulic suction filters is low.
You should note that high-precision filter elements of 10 µm or 25 µm cannot be used in the hydraulic suction filter. A too small aperture can generate great fluid resistance, leading to insufficient oil suction in the pump.
Consider the Installation Location and Size
The hydraulic suction filter should be able to be reliably installed in the system. You need to consider whether the size, interface specifications, and installation method of the hydraulic suction filter can be connected to the existing oil tank and suction pipeline. A suitable installation location can facilitate your daily maintenance.
Make Sure Compatibility between Materials and Media
You need to choose the material of the filter housing and filter element for the hydraulic suction filter according to the specific situation.
The material of the filter housing should be selected based on the working environment. Carbon steel is suitable for conventional drying conditions. The stainless steel material has strong corrosion resistance and is suitable for harsh environments such as high humidity and acidity or alkalinity. Aluminum alloy is lightweight and is commonly used in mobile hydraulic equipment.
The filter element material needs to match the hydraulic oil, and most of them are wire mesh such as stainless steel and brass.
Additional Auxiliary Components
Many hydraulic suction filters integrate bypass valves or differential pressure indication functions. They are used to open the bypass channel or give an alarm when the filter element gets clogged and the pressure rises.
You can also choose a hydraulic suction filter with a self-sealing valve. When you replace the filter element, the self-sealing valve will automatically close the oil suction channel, cut off the oil flow in the tank, and prevent leakage during maintenance.
FAQs
How should I Properly Clean the Suction Filter Element? Can I Use Paper Towels or Rags for Cleaning?
- The lint fiber in paper towels or rags is very difficult to filter out. It will get entangled in the gaps of hydraulic components along with the flow of hydraulic oil.
You can first soak the filter element in a cleaning solvent to dissolve the sludge. Then use compressed air to blow from the clean side to the dirty side. If possible, using an ultrasonic cleaning machine is the best option.
Can I Add a Magnet to the Hydraulic Suction Filter to Attract the Iron Filings?
You can use magnetic components to adsorb magnetic substances, but you cannot put ordinary magnets into the filter at will. This may alter the oil flow path or velocity, increasing the oil absorption resistance. Irregular magnetic fields may have an impact on components such as bypass valves and springs.
You can use dedicated magnetic filter elements in conjunction with regular filter elements.
How to Determine if the Hydraulic Suction Filter is Clogged?
If your system has a differential pressure gauge or blockage indicator, when the filter element is blocked by impurities, the pressure difference before and after filtration will abnormally increase or the indicator will give a warning signal.
In addition, problems such as poor oil suction by the oil pump, abnormal noises, and sluggish movement of the actuating elements are usually indications of blockage.
Can a Hydraulic Suction Filter be Used as the Only Filtering Component in the System?
- The hydraulic suction filter is used to initially intercept larger impurities. It cannot provide hydraulic oil that meets the final cleanliness requirements. In most hydraulic systems, you also need to use a hydraulic return filter or a pressure filter together to make the oil meet the cleanliness requirements.
When Installing or Replacing the Hydraulic Suction Filter, are there Any Other Things to Keep in Mind Besides the Filter Element?
You should inspect and make sure that all the seals are in good condition and properly installed. Before installation, you need to clean the old sealant, sludge, and other residues at the fuel tank or pipeline interface. These residues may become sources of pollution or cause leaks.
Final Thoughts
The hydraulic suction filter is the first line of defense for the hydraulic system. It keeps the cleanliness of the hydraulic oil at the pump inlet by blocking large particle impurities in the oil. This reduces component wear and lowers the risk of pump cavitation.
Target Hydraulics is a hydraulic component manufacturer with over 10 years of experience. If you have any further questions about the hydraulic suction filter, please feel free to contact us.
