Hydraulic Filter Types and Locations: A Practical Guide
Published by Filter Element Store on Jun 25, 2019
Hydraulic filters may look similar from the outside, but where a filter is installed determines the pressure it must withstand, the contamination it captures, and the components it protects. A suction strainer, pressure filter, return line filter, and off-line filter each perform a different job.
This guide compares the four most common hydraulic filter locations and explains the advantages and limitations of each.
Common hydraulic filter locations within a hydraulic system
Hydraulic Filter Types at a Glance
| Filter Type | Typical Location | Primary Purpose | Main Consideration |
| Suction Strainer | Between the reservoir and pump inlet | Stops larger debris before it reaches the pump | Must maintain very low pressure drop |
| Pressure Filter | Downstream of the pump | Protects sensitive valves and other components | Housing must withstand full system pressure |
| Return Line Filter | Between the working components and reservoir | Captures contamination before oil returns to the tank | Must handle return-flow surges |
| Off-Line Filter | In a separate reservoir-to-reservoir loop | Continuously conditions reservoir fluid | Requires a separate pump and motor |
1. Suction Strainers
Location: In the reservoir or suction line, immediately before the hydraulic pump.
A suction strainer provides last-chance protection against larger particles that could damage the pump. Because the pump must draw oil through it, a suction strainer normally uses relatively coarse media and a large surface area to keep restriction low.
Advantages:
- Helps prevent large debris from entering the pump
- Simple and generally economical
- Useful where reservoir contamination is a concern
Limitations:
- Fine filtration or a clogged element can restrict pump inlet flow and contribute to cavitation
- Does not capture contamination generated by the pump or downstream components
- In-tank strainers may be inconvenient to inspect and service
Best used for: Coarse pump protection when the hydraulic system has been designed to accommodate a suction strainer.
2. Pressure Filters
Location: Downstream of the pump, before the components that require protection.
A pressure filter removes contamination carried through or generated by the pump before the fluid reaches sensitive valves, servo components, cylinders, or other critical equipment. It may also be installed directly ahead of a particularly contamination-sensitive component as a point-of-use filter.
Advantages:
- Provides direct protection for sensitive downstream components
- Captures pump-generated wear debris
- Can support finer filtration where a high level of fluid cleanliness is required
Limitations:
- The housing must be rated for full system pressure and possible pressure spikes
- Typically costs more than a comparable return line filter
- Does not capture debris generated farther downstream until that fluid reaches another filter
Best used for: Protecting high-value or contamination-sensitive hydraulic components.
3. Return Line Filters
Location: After the hydraulic components and before the fluid returns to the reservoir.
A return line filter captures particles generated throughout the system before the oil re-enters the reservoir. These filters are available as in-line housings or tank-mounted assemblies and are common in many industrial and mobile hydraulic systems.
Advantages:
- Collects component wear debris before it reaches the reservoir
- Usually requires a lower-pressure housing than a pressure filter
- Tank-mounted designs can simplify installation and element changes
Limitations:
- Does not stop pump-generated contamination before it reaches downstream components
- Return-flow surges must be considered when sizing the housing and element
- Does not provide immediate point-of-use protection
Best used for: General system cleanliness and capturing wear debris before fluid returns to the tank.
4. Off-Line Filters
Location: In a separate filtration loop connected to the reservoir.
An off-line filter—also called a kidney-loop filter—uses its own pump and motor to draw fluid from the reservoir, pass it through the filter, and return it to the tank. Because it operates independently of the main hydraulic circuit, its flow rate and filtration cycle can be controlled without affecting machine operation.
Advantages:
- Provides continuous filtration even when the main circuit is not operating
- Maintains steady flow through the element for consistent filtration
- Can be equipped for fine-particle removal, water removal, or fluid conditioning
- Allows filter service without opening the main hydraulic circuit
Limitations:
- Requires a separate pump, motor, plumbing, and installation space
- Does not provide immediate protection between the main pump and a sensitive component
- Adds initial equipment and installation cost
Best used for: High-capacity reservoirs, contamination control programs, and systems that require continuous fluid conditioning.
Which Hydraulic Filter Location Is Best?
There is no single best filter location for every hydraulic system. Many systems use more than one filter so each location addresses a different contamination risk. For example, a return line filter may control general system cleanliness while a pressure filter protects a sensitive valve.
When selecting a hydraulic filter and replacement element, consider:
- System operating pressure and possible pressure spikes
- Normal flow rate and temporary flow surges
- Required micron rating and filtration efficiency
- Fluid type, viscosity, and operating temperature
- Bypass valve setting and dirt-holding capacity
- The components that need the most protection
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