The role and type of the hydraulic filter

Hydraulic filters are used to filter out debris from hydraulic oil in equipment circuits. Different types of filters must be used depending on the location in the circuit, and each type of filter has its own purpose.

What is the role of a hydraulic filter?

Hydraulic systems are the heart of construction and industrial machinery. Hydraulic filters play an important role in removing dust from the hydraulic oil that flows inside the circuits of hydraulic equipment. The reason why it is so important to remove dust is that oil contamination directly leads to machine failure. In fact, it is estimated that 70% of hydraulic equipment failures are caused by foreign substances in the hydraulic oil.

As machines are operated on a daily basis, the oil becomes increasingly contaminated by dust and sand from the outside and metal fragments due to wear of the metal. These particles are micron-sized, but if they get between metal parts, they can cause malfunctions. First, small cracks will appear, which will gradually spread as a result of repeated strain. Eventually the parts will be destroyed. In addition to failures, the efficiency of the machine itself is reduced due to the accelerated wearing out of its parts

Therefore, it is important to use filters to keep the  oil clean and protect the equipment. In other words, hydraulic filters are necessary to extend the life of hydraulic equipment and increase operating efficiency.

However, hydraulic filters are not just about removing dust. It is also important not to block the flow of hydraulic fluid. For example, a filter placed just in front of the pump has the role of keeping debris out of the pump, but if the mesh is too fine, the absorption resistance of the pump will increase, and cavitation will cause the pump to fail. Therefore, it is important to use an appropriate filter depending on the location in the hydraulic system.

Types of hydraulic filters

In the circuit of a hydraulic system, dust is generated everywhere such as in  the breather, tank, and pump. That is why multiple filters are installed for each location to protect the circuit. So what exactly are hydraulic filters? Let's understand the types and their roles, and install the appropriate filter for your machine.

(1)Suction line filter

This filter is installed on the line from the reservoir tank to the pump. Installed in front of the pump, it prevents dust from mixing into the pump and protects it. Various materials and shapes are available.

(2) In-line filter

This filter is installed on the discharge side of the pump. Installed in the line (delivery circuit) from the pump to the operating unit, it cleans up the oil before operation and protects the operating units such as control valves and cylinders. There is also a last chance filter installed just before the equipment to be protected.

(3)Return line filter

This filter is installed on the line returning from the moving section to the reservoir tank. It removes dusts generated by hydraulic components and external dusts mixed in from the cylinder lot to prevent debris from entering the tank.

(4) Off-line filter

This is an independent filter installed outside the hydraulic circuit with a pump motor. It removes dust inside the tank. When using it, there are cases when the cleaning on the line is insufficient, or when it is difficult to install a filter on the line. 

(5) Suction strainer

This filter is installed at the suction port of the pump in the reservoir tank. It protects the pump by preventing the suction of dusts into the tank. To prevent cavitation, the filter is characterized by a relatively coarse mesh filter such as wire mesh.

(6) Breather

This is installed at the air inlet (air breather) or refueling port (refueling port breather) of the reservoir tank. It prevents dust, dirt, and foreign matters from entering the tank during intake and exhaust or refueling. Some types are designed for dual use.


Hydraulic filters need to be replaced depending on where they are used and the type of oil, but each one has an important meaning to protect the machine. Use the most appropriate filter, keep the oil clean, and protect your hydraulic equipment from damage.