Pump datasheets in tenders: duty point, curves and deviations

What the duty point on a pump datasheet really fixes

Our guide to technical datasheets in tenders explains which cells the purchaser fills and which you fill. On a pump sheet, the purchaser's side is mostly process data: liquid, temperature, specific gravity, vapor pressure, viscosity, normal and rated flow, differential head and NPSH available. Everything you write follows from one hydraulic selection against those numbers.

Read the operating cases before you select. Many datasheets carry a normal point, a rated point and sometimes a minimum or maximum case for parallel running or future demand. The rated point is the guarantee point: it is what the performance test checks. The other cases decide whether the pump runs comfortably the rest of the time.

• Select so the rated flow sits close to the best efficiency point (BEP) of the impeller you offer. Many specifications set a band around BEP and ask you to state where the rated and normal points fall.
• Leave room on impeller diameter. Specifications commonly ask that a larger impeller can raise head later, so offering the maximum diameter for the casing can count against you.
• Check the minimum continuous flow against the buyer's minimum case. If the process can run below it, the buyer needs a recirculation line, and the evaluator will ask who supplies it.
• Check the shutoff head against the downstream design pressure. A steep curve plus test tolerance can push it higher than the buyer expects.

NPSH available, NPSH required and the margin evaluators look for

The buyer states NPSH available (NPSHA) at the pump suction. You state NPSH required, which manufacturers publish as NPSH3: the suction head at which the first-stage head drops by 3 percent. At NPSH3 the pump is already cavitating, so a margin is needed on top. The Hydraulic Institute's guideline on NPSH margin, ANSI/HI 9.6.1, defines that margin and recommends values by application (HI 9.6.1 contents (opens in a new tab)).

Buyer specifications usually turn this into a simple rule, such as a fixed margin in meters or a minimum ratio of NPSHA to NPSH3. Read which one applies and where it is measured. Some ask for the margin at the rated point; stricter ones ask for it over the whole operating range up to the maximum flow case.

If the datasheet asks for an NPSH test, it is a separate test from the performance test, with its own cost and time. Price it, and note whether it is witnessed.

Pump efficiency and power guarantees: what you sign up to

The efficiency and power you write at the rated point are guarantees, checked at the performance test within an agreed tolerance. The tolerance comes from the test code the tender names: API 610 for process pumps, ISO 9906 with a stated acceptance grade, or IS 9137 in many Indian utility tenders. Each code allows a different tolerance on flow, head, power and efficiency, so the same pump can pass under one and fail under another.

Head tolerance is not a free cushion. A Chemical Processing article on pump selection notes that API 610 allows a tolerance of plus or minus 3 percent of rated head, which on a very high-head pump is a large number of meters, and suggests buyers restrict tolerances on the datasheet when that matters (Chemical Processing, 2018 (opens in a new tab)). Look for such restriction notes before you rely on the code tolerance.

Some tenders also put a price on efficiency. Where guaranteed power consumption is loaded in evaluation, each extra kW adds a stated amount to your evaluated price, and liquidated damages per kW can apply if the test shows more. Research on BHEL power plant tenders found this pattern for guaranteed power. So a point of efficiency can decide L1 without changing your quoted price at all.

Motor, materials and seal data: the rows behind the hydraulics

Motor sizing is the row evaluators check most often. Size it for the end of the curve, at the largest impeller the casing allows if the specification asks for that, not for the rated point. Process pump specifications commonly set a minimum ratio of motor rating to pump power that falls as the motor gets bigger.

Seal data trips up many offers because it lives on a different sheet. If the pump datasheet says "Plan 53B" and your seal vendor quoted Plan 52, that difference belongs on your deviation sheet, even though the seal is a bought-out item.

Pump test requirements: performance, NPSH, mechanical run and witness scope

The test rows decide your shop schedule and part of your price. Read each one for three things: which test, to which code and grade, and who witnesses it.

• Performance test: the head, flow, power and efficiency curve, checked at the rated point against the guarantee. Note whether it runs with the job motor or a shop motor.
• NPSH test: confirms NPSH3 at stated flows. Not every pump needs it; price it only where asked.
• Mechanical run test: vibration, bearing temperature and sometimes noise over a stated run time.
• String or complete unit test: pump, motor and sometimes gearbox together. It needs the motor at your works on time.
• Dismantle and inspect after test: adds days, and sometimes a witness visit.
• Hydrostatic test of the casing and material tests such as PMI on alloy parts.

Witnessed tests need a test slot, the inspector's availability and notice periods written into the tender. If your test bed cannot hold the flow or power at full speed, say so and propose the method, for example a reduced-speed test with conversion, as a deviation.

How to present the pump performance curve and pump deviations

The proposal curve is the evidence behind your datasheet values, and evaluators read it before they read your covering letter. Give them one curve per tag or per identical group, with the curve number written on the datasheet.

1. Plot head, efficiency, power and NPSH3 against flow, in the units the datasheet uses.
2. Show the rated, maximum and minimum impeller diameters, with the offered one marked.
3. Mark the rated point and normal point, the BEP, the minimum continuous flow and the end of the allowable operating range.
4. State the liquid basis. A water curve for a viscous or high specific gravity liquid needs the correction shown, or the evaluator cannot compare it.
5. Write the maximum power at the end of the curve, because that is what your motor sizing rests on.

Pump deviations are usually hydraulic: efficiency below a stated minimum, NPSH margin short at one case, rated point too far from BEP, or no room left for a larger impeller. List each one with the value asked, the value offered and why, and include what it means for the buyer, such as extra power per year. Our guide to the technical deviation sheet covers how evaluators classify and load them.

Illustrative example: river water pumps for a Paradip fertilizer plant

A pump maker in Coimbatore receives an enquiry for two river water pumps, one working and one standby. The datasheet gives a rated point of 850 cubic meters per hour at 42 m head, water at 32 degrees C, NPSHA of 7.0 m, a maximum case of 1,020 cubic meters per hour for one pump running alone, a minimum efficiency of 82 percent and a power loading clause. All figures are invented for the example.

1. Hydraulic power at the rated point works out to about 97 kW. The best catalog selection gives 80.5 percent efficiency, so about 121 kW at the shaft.
2. NPSH3 is 4.6 m at rated flow, a margin of 2.4 m. At the maximum case, NPSH3 rises to 6.4 m while NPSHA falls to 6.8 m, leaving 0.4 m, below the 1.0 m the specification asks.
3. Maximum power at the end of the curve is 138 kW, so the team offers a 160 kW motor and shows the ratio.
4. Efficiency is 1.5 points under the minimum. Against a pump at 82 percent, that is about 2.2 kW more. At an assumed loading of Rs 1.5 lakh per kW, that adds about Rs 3.3 lakh to the evaluated price.
5. The team checks a larger casing size: it meets efficiency and margin but costs more and fits the baseplate differently. Engineering and sales compare both before pricing.

They offer the larger casing as the base offer and the smaller one as an alternative with two listed deviations, because the tender allows alternatives. Without the maximum-case check, the NPSH shortfall would have reached the evaluator as an unlisted difference on the curve.

AI on pump datasheets: where it saves typing and where engineers decide

A pump enquiry spreads duty data, motor rows, seal sheets and test requirements across several documents. TenderGenie's Datasheet Extraction pulls technical specifications out of your catalogs and the buyer's documents as organized data, and Filled-in Datasheet uses it to complete the buyer's own datasheet format for your engineers to review.

The Enquiry Checklist turns the requirements into what to supply, what you already meet and what is missing, such as a witnessed NPSH test or a seal plan your vendor has not quoted. See the pump manufacturers page for a worked enquiry in TenderGenie.

The hydraulic selection, the margin check at every case, the motor size, the choice between a base offer and an alternative, and each deviation stay with your engineers. Software can put the numbers in front of them with their sources; the signature on the datasheet is still theirs.

Questions and answers