Pressure Line Filter
A pressure line filter is the fine filter placed at the pump outlet and used to protect sensitive valves. Its rating is typically 3-10 micron and its body strength is selected above system pressure, for example 250-420 bar. It is standard in circuits with proportional and servo valves.
Why it is needed comes out of a simple geometry: in a proportional valve the radial clearance between spool and body is on the order of microns. A particle trapped in that clearance sticks the spool; the result is a growing deadband, increased hysteresis, or the valve not moving at all.
- Location: between the pump outlet and the valve inlet, as close to the valve as possible.
- Type without bypass: if a sensitive valve is being protected a body without bypass is preferred; rather than dirty oil passing through a clogged filter, flow is cut off.
- Pressure drop: typically 0.5-1 bar with a clean element; this value is energy lost from the system.
A significant portion of the behavioral problems experienced in proportional control comes not from electronics but from filtration. Checking the filter condition and the cleanliness class of the oil before changing settings keeps you from chasing the same symptom over and over.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods