Water-duty & liquid
HI 9.6.1 applies above 40 cSt
Awaiting Valid Duty Parameters
Adjust the parameters on the left to compute live hydraulic values, ranges, and sizing verdicts.
Sizing a pump for a viscous chemical?
Viscous duties need correction factors or a different pump family. Our engineers size pumps for the real liquid, not the water curve.
Viscous liquid pumping explained
Why the water curve lies
Centrifugal pump curves are drawn for water. Viscous liquids lose energy to internal shear in the impeller and casing, so the pump delivers less flow and head than the water curve suggests, and efficiency falls. The Hydraulic Institute’s HI 9.6.1 standard publishes correction charts used worldwide to convert a water-duty point to the viscous-duty point.
Below about 40 cSt the correction is negligible. Above it, the corrections grow quickly: at 100 cSt a typical pump may deliver ~95 % of water flow, ~90 % of head, and run ~85 % efficiency; at 500 cSt the numbers fall much further. This calculator applies typical chart values as approximations.
The three factors
Three factors are applied: CQ to flow, CH to head, and Cη to efficiency. Corrected flow = water flow × CQ; corrected head = water head × CH; corrected power = corrected flow × corrected head × SG ÷ (367 × corrected efficiency). The corrected point is what you compare with the pump curve — and the corrected power is what sizes the motor.
The tool returns all three factors plus the corrected duty and power for the entered SG.
When to change pump family
Above roughly 2000 cSt, centrifugal pumps become impractical — the corrections collapse and a positive-displacement pump (diaphragm, peristaltic, lobe) is the right family. Between 40 and 2000 cSt, corrected centrifugal duty works well for transfer and circulation. Teflow’s engineers apply the correction on every viscous duty — thermic oil, syrups, resins, lube oil — and supply or repair the right pump. Call +91 98251 62709 for a sizing check.
Technical & Operational FAQs
Q1.What is HI 9.6.1?
The Hydraulic Institute standard for viscosity correction of centrifugal pump performance. It publishes charts giving correction factors for flow (CQ), head (CH) and efficiency (Cη) as functions of viscosity, which convert a water-duty point into the viscous-duty point. This tool applies typical chart values.
Q2.At what viscosity does correction start?
Above about 40 cSt the correction becomes significant; below that, water-curve performance is close enough. The corrections grow rapidly with viscosity — always apply them above 100 cSt, where the efficiency penalty alone can reach 15–20 %.
Q3.How do I size a pump for viscous liquid?
Start from the required flow and head, apply the HI 9.6.1-style factors to find the water-duty point the pump must be selected for, then use the corrected efficiency for the motor power. The calculator does this in one pass.
Q4.Can a centrifugal pump handle thick oil?
Yes, within limits — typically up to a few thousand cSt with the right impeller design and corrected sizing. Above ~2000 cSt, efficiency collapses and a positive-displacement pump is the better choice for flow accuracy and power.
Q5.Does SG matter for viscous duty?
Yes — power scales with SG as always, and viscosity and SG are linked: dynamic viscosity cP = kinematic viscosity cSt × SG. Enter the liquid SG here so the corrected power is right.
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Need a custom hydraulic audit or specific duty curve verification? Call +91 98251 62709 or Request a Detailed Engineering Quote.