Strainer Pressure Drop Calculator
Pressure drop across a basket or Y-strainer from the open area ratio and screen geometry, using the Idelchik perforated-plate and mesh resistance forms.
When to use this calculator
Use when checking whether a strainer fits the hydraulic budget, particularly on a pump suction where a clogged element can pull NPSHA below the pump's requirement. The drop depends far more on the open area ratio and the screen's total area relative to the pipe than on the nominal size, so a strainer that seems generously sized can still be restrictive with a fine mesh. The tool separates the body loss from the element loss so the effect of changing mesh alone is visible.
Required inputs
- Element type — perforated plate or wire mesh
- Open area fraction f of the screen
- Screen-to-pipe area ratio R
- Body resistance coefficient, pipe velocity, and fluid density
Expected outputs
- Face velocity through the screen
- Element resistance coefficient ζ and K_element referred to pipe velocity
- Body, element, and total K
- Clean pressure drop, and the effect of a fouled element
Formula overview
f and R are dimensionless ratios, ζ and K dimensionless, v in m/s, ρ in kg/m³, ΔP in Pa.
Idelchik resistance forms:
R = A_open / A_pipe v_face = v_pipe · (f/R)
perforated plate:
ζ = [0.5(1−f)^0.75 + τ(1−f)^1.375 + (1−f)² + λ·λr] / f²
wire mesh:
ζ = 1.3(1−f) + ((1−f)/f)²
K_element = ζ · (f/R)²
K_total = K_body + K_element
ΔP = K_total · ρv²/2Worked example
Wire-mesh basket, open area fraction f = 0.35, screen area 3× the
pipe area (R = 3.0), body K = 1.5, water at 2 m/s, ρ = 998 kg/m³
ζ_mesh = 1.3 × 0.65 + (0.65/0.35)² = 0.845 + 3.449 = 4.29
K_element = 4.29 × (0.35/3.0)² = 0.058
K_total = 1.5 + 0.058 = 1.56
ΔP = 1.56 × 998 × 2²/2 = 3 110 Pa ≈ 0.031 bar
The generous screen area makes the element almost free — the body
dominates. Halve the screen area and the element term quadruples.Common mistakes
- Sizing on the clean drop only. A strainer exists to collect debris, and a partially blinded element can multiply the loss many times. Set the alarm and the hydraulic allowance on a fouled condition, not a new one.
- Putting a fine strainer on a pump suction without checking NPSHA. The drop comes straight off the available suction head, and a blinding start-up strainer is a classic cause of cavitation during commissioning.
- Assuming a bigger nominal size fixes it. What matters is the screen open area relative to the pipe and the open area fraction of the mesh — a larger body with the same fine mesh and the same area ratio barely helps.
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