The correct selection of whether a simple suction strainer or inline filtration is required depends on the pump type, viscosity, and maximum allowable vacuum, as well as the pump manufacturer's requirements.
Suction line filters should be designed so that 0.25 bar vacuum is not exceeded. But the decisive factor is what negative pressure the pump manufacturer allows in order to avoid cavitation damage to the pump.
For protection, suction line filters are monitored with a vacuum indicator. Electric or electric-optical vacuum indicators are also able to switch off the pump as soon as the maximum permissible vacuum is reached.
In the tank below the oil level, e.g. as simple suction strainers with a filter fineness >60 µm.
As an in-tank filter with a return valve that prevents oil from leaking from the tank when the element is changed.
As an in-line filter positioned upstream of the pump.