Base duty & trim
Closed-impeller limit 20–25 %
Awaiting Valid Duty Parameters
Adjust the parameters on the left to compute live hydraulic values, ranges, and sizing verdicts.
Need an impeller trimmed or re-cut?
Our workshop trims, rebalances and re-cuts impellers for chemical pumps, and advises when a new impeller beats machining.
Impeller trimming explained
The cheapest retrofit
Trimming the impeller is the most economical way to match a pump to a lower duty — no VFD, no motor change. The affinity laws govern the result: flow changes in direct ratio with diameter, head with the square, power with the cube. A 10 % trim (90 % diameter) gives 90 % flow, 81 % head and 73 % power — a 27 % power saving.
The calculator applies these ratios and shows the new duty and the new diameter to machine.
How much can you trim?
Closed impellers can typically be trimmed 20–25 % of the diameter before efficiency collapses; open and semi-open impellers allow less, around 15–20 %, because tip clearance losses grow quickly. Beyond the limit, a new impeller is cheaper than the efficiency you lose.
The tool warns at 20 % and blocks beyond 25 % with a recommendation to buy a new impeller. Efficiency also falls by roughly 1 % per 10 % of trim — fine for small trims, decisive at the limit.
After the trim
A trimmed impeller must be rebalanced — machining removes metal unevenly, and an unbalanced impeller shakes seals and bearings apart. The affinity result is also a first cut: verify the new duty on the actual curve and check the motor power, since a big trim drops the absorbed power and may let the motor run at part load.
Teflow’s workshop trims, rebalances and re-cuts impellers in PTFE, PFA, PP and SS for chemical pumps across Gujarat — call +91 98251 62709 for a quote with your duty point.
Technical & Operational FAQs
Q1.How do I calculate trimmed impeller diameter?
New diameter = current diameter × √(new head ÷ current head), or simply current diameter × (1 − trim % ÷ 100). For 10 % trim on a 200 mm impeller: 200 × 0.9 = 180 mm. Flow scales by the same ratio, power by its cube.
Q2.How much can I trim an impeller?
Closed impellers: 20–25 % of diameter. Open and semi-open impellers: 15–20 %. Beyond that, efficiency collapses and a new impeller is cheaper. The calculator warns at 20 % and blocks beyond 25 %.
Q3.Does trimming reduce power?
Yes — power follows the cube of the diameter ratio. A 10 % trim cuts absorbed power to about 73 % of the original, a 15 % trim to about 61 %. That is why trimming is often the cheapest energy retrofit on an oversized pump.
Q4.Should I trim or buy a new impeller?
Trim when the duty is modestly lower (within the 20–25 % limit) and the pump family stays right. Buy a new impeller when the trim needed exceeds the limit, when the impeller is worn, or when the liquid is erosive — machining worn metal is rarely worth it.
Q5.Do I need to rebalance after trimming?
Yes. Machining removes metal unevenly and an out-of-balance impeller causes vibration that destroys seals and bearings quickly. Professional shops trim to the drawing, rebalance, and verify the diameter — Teflow’s workshop does all three.
Related Engineering Tools
Affinity Laws Calculator
System Curve Tool
Motor Sizing Calculator
Teflon Pump Manufacturing
Pump Repair Service
Pump Consultancy
Need a custom hydraulic audit or specific duty curve verification? Call +91 98251 62709 or Request a Detailed Engineering Quote.