In-tank hydraulic suction strainer (wire-mesh pump inlet strainer)

01

Size the strainer for a small clean pressure drop

HYDAC advises that its suction strainer elements be sized for clean element pressure drops of no higher than 0.5 to 0.7 psi, and states that pressure drop will be below 2 psi within the recommended flow range with a fluid of 141 SSU and specific gravity 0.86. Its SFE in-tank elements run from 3/8 in NPT at a nominal 3 gpm to 3 in NPT at 100 gpm, and HYDAC notes that high-velocity or low-temperature applications may require a strainer with a higher flow rating. [1] Editorial calculation: 0.5–0.7 psi ≈ 0.034–0.048 bar; 100 gpm ≈ 379 l/min.

Filtrec rates its FS1 strainers at a pressure drop of 0.02 bar with a clean element and oil of 32 cSt and density 0.875 kg/dm³, gives 0.02 bar as the maximum recommended pressure drop, and lists flows from 16 l/min for a G 3/8 connection to 500 l/min for G 3 in its sizes 10 to 40. [2]

MP Filtri rates its STRC and MPAC suction strainers at a pressure drop of 0.08 bar with oil of 30 cSt and density 0.86 kg/dm³: 19 l/min at 3/8 in, 126 l/min at 1 in, 480 l/min at 2 in and 995 l/min at 3 in. It sizes suction filters on the total pressure drop of housing plus element, with corrective factors for element type and viscosity. [3]

Editorial note: the three makers rate flow at different pressure drops (0.02 bar, 0.08 bar, and 0.5–0.7 psi) and viscosities, so compare strainers only at the same Δp and fluid. Give the supplier the pump flow, the lowest start-up oil temperature and its viscosity, and the pump's permitted inlet pressure.

Send the pump type and flow, suction port size and thread, fluid type and viscosity at the coldest start, reservoir minimum oil level and space under the pipe, required mesh rating, bypass requirement, magnet option, and operating temperature range.

02

Choose a coarse mesh and decide on the bypass

Suction strainers screen coarse particles. HYDAC offers 74 µm (200 mesh) and 149 µm (100 mesh) stainless steel wire screen; its magnetic suction separators come with 74 µm, 300 µm (50 mesh) or 850 µm (20 mesh) screens. [1] Filtrec lists stainless steel wire mesh of 125 µm and 60 µm and zinc-plated steel mesh of 250 µm. [2] MP Filtri names 60 to 125 µm as the main gross filtration grades for its suction filters. [3]

A bypass valve opens when the element clogs or the oil is cold and thick. HYDAC's opens at 3 psi, to reduce high pressure drops caused by contaminated elements or high-viscosity fluid during cold starting. [1] Filtrec's is set at 0.25 bar, with a differential collapse pressure of 1 bar under ISO 2941. [2] MP Filtri's STRC bypass opens at 0.03 MPa (0.3 bar), and its wire mesh element has a 1 bar Δp rating. [3] Editorial calculation: 3 psi ≈ 0.21 bar.

HYDAC states that suction strainer elements are only intended to protect hydraulic pumps against catastrophic failure caused by coarse contaminant, should be inspected and cleaned regularly, must always be mounted below the minimum oil level of the reservoir, and should not be the only filtration in a hydraulic system; pressure and return line filters must handle fine contaminants. [1] MP Filtri describes placing suction filters under the fluid head to use the fluid's static pressure and reduce the risk of cavitation. [3]

03

Compare suction strainer arrangements

The arrangements below come from the catalogues reviewed.

04

Mesh, core, connector and bypass valve

The three catalogues describe the same build: a wire-mesh screen on a perforated core between a threaded connector and an end cap.

05

Quote the strainer on flow at a stated pressure drop

Flow is meaningful only with its pressure drop and viscosity; the fields below carry the catalogue values where a source gives them.

06

Send the pump, fluid and reservoir data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Pump: [type; flow; inlet port]
Fluid: [type; viscosity at coldest start]
Strainer: [mesh rating; flow at stated Δp]
Bypass: [setting or none]
Reservoir: [minimum oil level; clearance]
Connection: [thread or flange]
Options: [magnet; shut-off valve]

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