Orifice Permanent Pressure Loss Calculator
Estimate the unrecovered (permanent) pressure loss across an orifice plate from its β ratio and differential pressure, and the pumping power that loss costs.
- Δϖ/ΔP = [√(1 − β⁴(1 − C²)) − Cβ²] ÷ [√(1 − β⁴(1 − C²)) + Cβ²] = 0.6295
- Δϖ = 0.6295 × 250 mbar = 157.4 mbar
- Power = Q × Δϖ ÷ η = 0.625 kW
Permanent Pressure Loss (ISO 5167-2)
Approximation: Δϖ ≈ (1 − β1.9) × ΔP
Pumping power = Q × Δϖ ÷ η
Δϖ is the permanent pressure loss measured between about 1D upstream and 6D downstream, ΔP the meter differential pressure, β the diameter ratio and C the discharge coefficient (about 0.6 for orifice plates).
Worked example
An orifice with β = 0.6 and C = 0.605 at 250 mbar loses about 63 % of its DP, 157 mbar. At 100 m³/h with a 70 % efficient pump that costs about 0.63 kW, or 5,470 kWh a year.
Frequently Asked Questions
What is permanent pressure loss?
The part of the orifice DP that is not recovered downstream. It is lost as friction and turbulence and must be supplied by the pump or compressor.
Is permanent loss the same as the meter DP?
No. The meter DP is measured close to the plate; some of it recovers downstream, so the permanent loss is always smaller.
How can I reduce the loss?
Use a larger β with a lower DP range, or a venturi, flow nozzle or a non intrusive meter such as a magnetic or ultrasonic meter.
Learn more on the blog
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