Hydraulic filters are integral parts of systems using hydraulic power. A clean hydraulic system is crucial in guaranteeing that oil retains its qualities and performance over time. This is necessary as hydraulic systems are at risk of contamination from low-quality liquid, wear of components or ingression from seals. A hydraulic filter is designed to filter oils and other hydraulic fluids to keep the system clean. Furthermore, hydraulic filters prevent hydraulic installation applications from increased degradation.
About one million particles larger than one micron enter a hydraulic system per minute. As hydraulic oil is easily contaminated, these particles may cause damage to components in the absence of an effective hydraulic filtration system. Metal parts entering the hydraulic system oil can also accelerate degradation. An effective hydraulic filter continually removes particles while cleaning the oil in the system.
Hydraulic filter ratings are designed to measure the effectiveness of filters in cleaning and maintaining systems. Just having a filter, even if it performs well, isn’t enough to ensure clean fluid and the protection of the components. To be certain of contamination levels, it’s important to sample the fluid as it flows through the system.
The ISO 4406 Code is the measuring and reporting standard for contaminant levels and fluid cleanliness in hydraulic filter systems. The code consists of numbers that provide information on the quantity and size of particles in the system. A logarithmic measurement of the number of contaminants is published based on the particles found in 1 ml of fluid. The lower the ISO cleanliness rating is, the better the filter is at thoroughly eliminating contaminants. This indicates the filter’s ability to extend the life of hydraulic system components.
A hydraulic filter’s beta ratio is another method of determining its efficiency. The beta ratio is based on the amount of contaminant particles upstream of the filter divided by the downstream number. To come to this conclusion, the beta ratio is deducted by one, then divided by the beta ratio and multiplied by 100. This determines the percent efficiency of a hydraulic filter for a contaminant size. A higher beta ratio indicates a filter that performs well.
Hydraulic Filter Types
Due to the wear of components and other factors, hydraulic systems have an initial solid contamination that’s prone to increase during operation. Therefore, it’s crucial to use hydraulic filtration that maintains the required contamination class. Every system typically needs more than one filter. The hydraulic filter type depends on the location within the hydraulic system. Filters are located between the actuators and the pump, and the tanks and actuators.
Several types of hydraulic filters are available on the market. They include:
Return filters prevent particles from entering the system and filter hydraulic fluid prior to it returning to the tanks. They are located downstream from all components.
In-line Hydraulic Filters
In-line hydraulic filters are used directly on the pressure line in order to protect an individual or set of components.
Hydraulic Suction Filters
Hydraulic suction filters are fitted onto the suction line and are usually made from steel wire mesh. It’s important that they’re sized properly to avoid pump cavitation. Suction filters protect the pump from course contamination.
Hydraulic filter assemblies are available to order for offline systems and others, including:
- Dry and oil bath air filters for industrial engines and air compressors.
- Water and fuel filters for marine engines.
- Gas filtering elements.
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A hydraulic filter helps to remove particles and clean the oil on a consistent basis. The presence of metal parts in hydraulic system oil, like iron and copper, increase degradation. Therefore, an efficient hydraulic filter is measured by its ability to remove contamination via high dirt-holding capabilities. Most systems contain more than one hydraulic filter. Pressure filters are those that rest between the pump and actuators. Low pressure or return line filters are situated between the actuators and tanks.
The basic hydraulic filter components are as follows:
- The filter head is the ported casting that fluid enters and exits the filter from. It may also act as a mounting pad.
- A filter bowl is a vessel that threads into the filter head to contain and protect the element. This helps contaminated fluid to flow evenly around the outside of the element. The clean fluid then exits through the centre of the element.
- The element is the cartridge that holds filter media. It traps contaminates flowing in the system fluid.
- A bypass valve is designed to protect the hydraulic system when it’s overloaded with contaminates.
If a filter is clogged with contaminants a pressure drop occurs and the fluid can’t pass freely through it. There are two things that happen once the pressure drop reaches a critical value. If the hydraulic filter setup includes a bypass valve, the fluid will bypass the filter when the pressure drop reaches a critical point. Therefore, the fluid is not filtered and new contaminants pass unobstructed.
In clogged hydraulic filters that don’t have a bypass valve, the pressure drop increases until the filter element collapses. This results in contaminants flowing freely through the system and contaminating the filter itself. The pressure drop, in some systems, may result in a significant increase in pressure upstream of the filter. In the event that pressure reaches extreme levels and the filter doesn’t collapse, other system components are at risk of serious damage.
With regard to equipment damage, time and costs, a clogged hydraulic filter can cause serious problems. To rectify issues, the cause needs to be investigated and identified. Following this, the system needs to be flushed to remove contamination. Damaged components, such as hydraulic oil filter pumps or motors, need replacing or repairing.
Furthermore, new filters must be installed in the system before recommencing. The downtime required for this process, combined with repairing damaged components, can be expensive. However, changing hydraulic filters avoids these complications.
In terms of the timeframe for changing hydraulic filters, there are two options to consider. Generally, based on hours of service, equipment manufacture guidelines indicate when filters should be changed. However, following this advice may result in changing a filter before it’s necessary and therefore wasting some of its capacity. Alternatively, if a change is overdue, the efficiency of a system may be compromised. It’s important to gain experience with equipment in order to schedule hydraulic filter changes appropriately.
A different option is the use of an element condition indicator that measures the pressure drop in the filter. The indicator displays when the pressure drop reaches a critical level and highlights the need to change it. This approach allows for consistent monitoring of pressure drops across all filters, along with potential issues that may result in system failures.
Hydraulic filters are designed to protect hydraulic system components from damage due to oil contamination. It’s estimated that a large percentage of fluid power failures are a result of contamination problems. Fluid can become contaminated for a variety of reasons. They include general wear of the components, substandard plumbing and the introduction of new fluid or components. Therefore, hydraulic filters are crucial in maintaining contaminant-free systems.
A variety of filter types offer different configurations and uses. A bag filter utilises a cloth bag to push the hydraulic fluid through the system. In turn, solid contaminants are stopped from flowing through the bag with it. This method is successful for filtering rust, dirt and any particles from cylinder rods entering the system. Magnetic filters use magnetically charged plates to attract metallic contaminants. For screen filters, small wires are woven together to produce a metallic cloth that’s designed to fit exact pore sizes. This method is particularly useful in the process of choosing the right filter when the size of the contaminant is already identified.
Additionally, choosing the right filter should be based on the overall construction, including the filter and the alignment. Before buying a filter, it’s crucial to know whether or not the system requires hydraulic filter housing. In terms of alignment, there are several options available. They include:
- In-line alignment refers to a system whereby the inlet, outlet and filter are lined up together.
- Off-line alignment is when the hydraulic filter isn’t on the main systems loop.
- Duplex configuration is when two filters are used and combined for ease of maintenance.
- Return-line configuration ensures all contaminants are caught upon entering the system.
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