The single most critical variable in determining the flow capacity of a filter is the viscosity of the fluid passing through it. Pressure drop (Differential Pressure) produced by flow through a filter assembly is directly proportional to the viscosity of the fluid being filtered. At any given flow rate, a lower viscosity fluid will produce less pressure drop (and greater flow capacity) than that of a higher viscosity fluid.

A fluid's viscosity is governed by its temperature. As a fluid's temperature increases, its viscosity decreases. Use a temperature versus viscosity chart to determine the viscosity of the fluid used in your system at its normal operating temperature.

All pressure drop data found in this catalog is based on 150 SUS oil. If the fluid to be filtered in your application has a viscosity of 150 SUS at the system's normal operating temperature, pressure drop values can be taken directly off the graphs. If the fluid's viscosity is not 150 SUS, use the formula below to estimate the pressure drop.

Filter Application Guidelines Suction Strainers Maximum pressure drop: 1" Hg Maximum line velocity: 5 feet per second Suction Line Filters Maximum pressure drop: No more than 50% of the Maximum allowable vacuum recommended by pump manufacturer, at normal operating temperature with clean element. Maximum line velocity: 5 ft per second Return Line Filters Maximum pressure drop: No more than 50% of the filter by-pass valve setting at normal operating temperature with a clean element. Maximum line velocity: 15 ft per second Pressure Filters Maximum pressure drop: No more than 50% of the filter by-pass valve setting at normal operating temperature with a clean element. Maximum line velocity: 25 ft per second

Using tank diffusers helps prevent air entrainment in hydraulic oil. Air sucked into a pump can cause cavitation and other system damage.

Diffusers and suction strainers should be mounted in the bottom 1/3 of the reservoir. They should be separated from one another by baffles.

Breather filtration rating should be equal to or better than system filtration rating.

On systems with a fairly constant fluid level in the reservoir, a pressurized filler breather cap increases pump inlet pressure. Generally, the more pressure a pump has at its inlet, the quieter it will run.

Velocity Through Piping (Feet per Second)

Filter without by-pass valve. Example: Strainers, Spin-on Heads, Tank Top, & High Pressure Filters. Filter with magnet. Example: Strainers Filter with condition indicator. Filter with by-pass and reverse flow valves. Check Valve.