What is a Hydraulic Filter? How to Choose a Hydraulic Filter?

What is a Hydraulic Filter? How to Choose a Hydraulic Filter?

Hydraulic filters are an important component used in hydraulic systems. These filters remove solid particles and other contaminants in the hydraulic fluid, ensuring longer life and safer operation of the components in the system.

Hydraulic filters are designed to remove various types of contaminants. These may include solid particles, water, oxidation products of oil and other contaminants. Filters help protect pumps, valves, cylinders and other sensitive components in hydraulic systems.

Hydraulic filters usually contain a pressurized cartridge or element. Cartridge type filters contain pre-installed filter elements and are generally easy to replace. Element type filters, on the other hand, have a body to which the filter element is directly mounted.

Filter selection is critical to the performance and reliability of hydraulic systems. Choosing the right filter type ensures effective removal of contaminants from the system. Additionally, regular maintenance and replacement of filters ensures long life of the hydraulic system and maximum performance.

Various types of filters are available for hydraulic systems, each designed for a specific application or requirement. Here are some commonly used types of hydraulic filters:

1. **Pressure Filters**: These filters are used in high pressure lines in the hydraulic system. They are made of high pressure resistant materials and can usually be cartridge type or element type.

2. **Suction Filters**: Suction filters ensure that hydraulic fluid is cleared of contaminants before entering the system. These are installed in the suction line of the hydraulic pump and usually capture large particles and other large contaminants.

3. **Return Filters**: Return filters filter the line where hydraulic fluid returns to the hydraulic tank. These filters capture contaminants that may occur in the system and ensure the cleaning of the liquid.

4. **High Pressure Filters**: High pressure filters are specially designed filters that can withstand very high pressures in hydraulic systems. These filters are used in high pressure lines and are important to ensure the reliability of the system.

5. **Air Filters**: In hydraulic systems, air can come into contact with the liquid in the system and cause contamination. Air filters trap air bubbles and other airborne contaminants in the system.

6. **Water Filters**: In some hydraulic systems, water can be an undesirable component in the system. Water filters increase the performance of the system by removing the water in the hydraulic fluid.

These filter types are selected and used in accordance with the specific needs and operating conditions of hydraulic systems. It should be noted that each filter type serves a specific purpose and needs to be taken into account in system design.

There are three types of filters in hydraulic circuits: pressure, return and storage (suction) filters, which ensure the cleanliness of the fluid in order to protect the system elements from wear and prevent the failure of the machines from starting.

Hydraulic filters are an important component used in hydraulic systems. These are designed to filter and remove contaminants (such as particles, water, etc.) and other contamination from hydraulic oil. Cleanliness is very important in hydraulic systems because contamination can cause wear, damage and performance degradation in the system.

There are various types of hydraulic filters and they are based on different filtering principles. Some use mechanical filtration to filter out solid particles, while others use the principles of adsorption or chemical reaction to remove chemical contaminants in the liquid.

The basic components of hydraulic filters are:

1. Filter body: The structure where the pollutants are kept and the filter elements are located.
2. Filter element: A filter material designed according to particle sizes. This element retains contaminants in the oil and allows clean oil to pass.
3. Filter head: The structure that connects to the filter body and provides support for the filter element.
4. Pressure drop indicator: A device that measures flow resistance in the filter and indicates filter blockage.

Hydraulic filters are important to ensure that hydraulic systems operate efficiently and reliably. Regular maintenance and replacement of filters is critical to maintaining system performance.

Pressure line filters are examined in 2 main groups. The filters on the system at high pressure (420bar) and low pressure (21bar) have sensitive filtration capabilities at levels of 3µ, 6µ, 10µ, 20µ, 25µ. The material required for such sensitive filtration is obtained by using laminated products based on Defender Fiberglass (Defender microglass). While 25µ filtration is performed on the system returns, chrome (mesh) filters are used in the suction line.
According to scientific studies on hydraulic systems, 70% of the problems in the systems are caused by wear (50% mechanical wear, 20% corrosion), 15% are caused by accidents and the last 15% are caused by exceeding the service life. With the quality standard achieved thanks to the high dirt holding capacity of the raw materials used in our products, it increases the performance and lifespan of large cylinders, servo valves, hydraulic motors and other machines and parts, which are the most important elements of the system, and ensures uninterrupted operation of the hydraulic system.

POLLUTION, POLLUTION TYPES AND SOURCES
1.1. Pollution Definition
More than 75% of the malfunctions in hydraulic systems are caused by oil contamination.
It is a fact determined as a result of many years of statistics.

Pollution;
• Production losses
• Component replacement costs
• Oil change costs
• High stopping rate
It produces results such as.

Hydraulic Oils,
• Energy transfer
• Lubrication of moving parts
• Heat transfer
• They have basic functions such as providing sealing between moving parts.
Failure to provide one of these may cause a large production line to stop working and thus cause large production losses.
• Clogging of orifices
• Wear and rust of parts
• Deterioration of the chemical properties of the oil
• Oil additives lose their properties
• Results such as deterioration of viscosity properties prevent the ideal oil from fulfilling the tasks listed above to the desired extent. We call this phenomenon oil contamination, oil pollution.

1.2. Pollution Types and Sources
1.2.1. Particle Pollution, Sources and Precautions Hydraulic system fluid coming from the refinery, new oil is not suitable for the hydraulic system.
This needs to be filtered and made suitable for use. Particles in the oil are collected in 2 groups. Particles smaller than 5 microns and particles larger than 5 microns; Pieces smaller than 5 microns cause long-term corrosion damage to hydraulic system components. Figure 1-a shows how the particles flowing in the system along with the oil erode the surfaces over time. Pieces larger than 5 microns cause immediate damage. Figure 1-b shows how a piece stuck between the valve slide and the body renders the valve unusable.

Particle, particles into oil;
1. Hydraulic system during manufacturing and assembly
2. With new fluid
3. Extern during operation
4. From inside during work (Intern)
are added.

1.2.2. Water Pollution, Sources and Precautions
Just because the hydraulic fluid is free of particles does not mean that it is clean. The water in the oil creates pollution, just like the particle, and must be removed from the fluid. Water is either free or bound in the oil. The amount of water allowed in oil is given in Table 1 according to fluid types. Table 1. Permissible amounts of water in oil

In hydraulic systems operating with fluid contaminated with water
• Corrosion on metal surfaces
• Wear
• Shortening of bearing life
• Reduced effect of additives
• Change of viscosity
• Negative results such as increased electrical conductivity are observed.

Sources of water pollution are;
• Defective cylinder seals
• Tank leak
• Condensation-condensation
• Water coolant leaks may occur.
Various methods are used to purify oil from water. Due to the specific gravity difference, the free water in the oil will sink to the bottom. The water collected here is discharged through the drain valves in the tank. Apart from this, Absorption is obtained from oil water by using centrifuge and vacuum dewatering methods.
is separated. In the absorption method, gel-based chemicals are used as filter elements and bind the free water present in the hydraulic fluid. This method is suitable for low flow systems. In the centrifuge method, it is possible to separate only free water from oil thanks to centrifugal forces and specific gravity difference. This is mostly applied for high volume systems. Their efficiency is not high.
Water extraction method under vacuum; Water, which boils and evaporates at 100°C under normal conditions, evaporates at lower temperatures under low pressures, that is, under vacuum. Free or bound water present in the fluid sent to the vacuum chamber at a certain temperature is removed from the fluid.
It is separated and evaporated from the oil. This method is used for high flow systems and the efficiency is high.

1.2.3. Air Pollution Sources and Precautions
There may be free or bound air in the fluid. Especially the free air in the fluid must be reduced. With the pressure applied on the air in the fluid, the local temperature rises excessively, thus the additives in the oil burn and even the chemical structure of the oil deteriorates. The air in the oil causes the oil to lose its incompressibility feature, so the fluid used in a high-performance hydraulic system must be incompressible.

Air in the fluid;
• Decrease in lubrication properties
• Increase in oil temperature
• Efficiency decrease in power transmission
• Foaming of the oil in the tank
• Undergoing chemical change
• Faster oxidation of metal parts
• It creates negative effects such as increasing the wear rate with oxidation.
Air to the system;
• From existing leaks in the system
• From the tank vent

3. FILTER ELEMENT TYPES AND SELECTION CRITERIA
3.1. Filter Element, Material
Filter elements are produced by shaping materials such as metal, wire, paper, fiberglass or synthetic fiber. These elements are generally examined in two categories.

1. Surface filtration
2. Deep filtration

The elements that filter the surface are produced as wire mesh or metal. It is possible for particles to pass through certain gaps created on the filter surface, and all particles above the size are captured on the surface. See Figure 3 deep filtration elements cellulose
and is produced from fiberglass based materials. The filtering process is done at a certain depth as seen in Figure 4.

3.2. Filter Element Cleaning Degree Particle Separation Efficiency from the Fluid β Value The quality of the filter element is determined by the β value of that element. In order to determine the β value, a test known as the multipass test must be applied to the filter element. Multipass test filter
It is a standard used to determine element performance.

3.1. Filter Element Life
Filter element life is proportional to its dirt holding capacity. When the element begins to become dirty, the passages through which the fluid passes are clogged with particles. However, the blockage in the first period occurs because there are enough other transition points for fluid passage.
It does not cause any pressure loss. During filtration for a long time, the Δp pressure difference will increase very slowly. The pressure increase rate at points close to the filter element's maximum life is very high. Figure 7 conveys the pressure increase over time. Δp
When the pressure difference reaches a certain point, the filter prevents the passage of heavily contaminated fluid. This element needs to be replaced. The lifespan of filter elements varies depending on the material they are manufactured from. Life of paper fiberglass and multi-layer fiberglass elements in Figure 8
is shown

3.2. Filter Body Selection
The filter body is the component that contains the filter element and connects it to the hydraulic system. Thanks to the inlet and outlet connections on the body, the filter element is connected to the hydraulic system, and in addition, it undertakes additional functions such as mechanical assembly of the filter, providing by-pass opportunity and pollution indicator. First of all, pressure plays an important role in the selection of the body. In addition, mounting method and connection dimensions are filter design criteria. Filters are generally designed for suction, pressure and return lines. Suction and return filters are designed for pressures lower than 34 bar, while pressure filters are designed for the pressure range of 100-420 bar.
is done. By pass valves open when the filter is clogged and allow the oil to flow under a certain pressure. This filter prevents the element from disintegrating at high pressures and protects the pumps from the danger of cavitation when used in suction. The by pass valve is blocked or
When not in use, the filter element must be strong enough to withstand the system pressure. The Δp pressure loss criterion is one of the important ones when choosing a filter. When the filter element is clean, a ratio of 1/2 or 1/3 must be established between the Δp1 measured during flow and the Bypass opening Δp2 pressures. For example, if the by pass pressure is determined as 3.6 bar for the hydraulic system flow rate of 50lt/min; The total pressure loss of the filter (body + element) that should be used in the system should not exceed the limit of 1.2 bar and 2.4 bar.

3.3. Filter Types
Filters are examined in 4 groups according to their location on the system: suction, return, pressure and Off-Line.

3.3.1. Suction Filters
They are located in pump suction lines and undertake the task of protecting the pumps from pollution. They can be mounted inside the tank or even outside the tank with a body. There is a danger of cavitation in pumps due to high Δp due to contamination of suction filters and flow limitation. This
For this reason, it is necessary to follow the recommendations of pump manufacturing companies.

3.3.2. Pressure Filters

They are placed between the pump and the system, and a pressure filter suitable for the pressure and flow rate of the flowing oil must be selected. Pressure filters can be used for the entire system as well as to protect sensitive components such as proportional and servo valves.

3.3.3. Return Line Filters
It is the most suitable filter type for hydraulic systems. Its function is to keep the oil returning to the tank clean. In the system, the pollution that occurs during operation is retained by the return filter, which is the last component in the tank return. Since it is in the return line, the pressure is quite low. Return filters can be used as twins, and when one gets dirty, the other one is activated, and maintenance operations such as dirty element cleaning or element replacement can be easily carried out. Return filters can be used with or without By pass.

1-Microscopic Analysis
In this method, after the fluid is passed through a clean filter, the filter element is examined under a microscope. Pollution is attempted to be determined visually using human initiative. This is a method with a high error rate and low expression ability. 2- Analysis with laser particle counter In this method, while the fluid passes through a pipe, both the number and size of all particles up to 2 microns in it are determined with the help of laser. With this method, highly accurate and precise measurements in accordance with ISONAS standards regarding part contamination can be made.

RESOURCES
[1] The Handbook of Filtration Parker Hannifin Hydraulic Filtration Division
[2] Filtration Technology, Bulletin 0241-B1, Parker Filtration Division
[3] Hydraulic and Lube Filtration, 2300-000-8 USA, Global Filtration Technology, PH Hydraulic Filter
Division