Short answer: Ask for the curve and its identity card: exact model and power version, voltage/frequency, test liquid and conditions, flow and head units, the required duty point, tolerances and document revision. A Q–H line copied into a catalog is not enough to approve an OEM sample or a performance claim.
The curve that looked right—but belonged to the wrong version
Imagine a buyer comparing two compact plastic pumps. Both brochures list a similar maximum head and maximum flow. One quotation covers a 230 V / 50 Hz motor; the intended destination market needs a 120 V / 60 Hz version. The buyer cannot assume the same curve applies simply because the housing looks identical. Motor, impeller and electrical design may vary by version. A supplier should identify which data belongs to the unit actually being quoted.
A centrifugal pump curve shows the relationship between flow Q and head H under stated conditions. It does not say that the two maximum values occur together. The useful comparison is the flow available at the customer's total working head.
Six fields that belong beside the curve
| Buyer asks | Why it matters |
|---|---|
| Exact model, power and electrical version | Prevents using a different motor or variant's graph |
| Flow/head units and axis scale | Avoids GPH, L/min and m³/h conversion or plotting errors |
| Test liquid, temperature and setup | Explains the basis and limits of the result |
| Test method, instrument and record reference | Makes the evidence auditable rather than a marketing image |
| Required duty point and acceptance tolerance | Converts a maximum claim into a purchasing decision |
| Document date, revision and approval | Stops an obsolete curve from being used on a new carton |
For a system with a hose and fittings, the operating point depends on static lift plus friction and local losses at the intended flow. If the buyer cannot calculate the friction loss yet, supply the hose internal diameter, length, elevation and connection details and ask engineering to evaluate the duty. A line on the pump chart cannot tell you the installed flow without that system information.
A simple approval conversation
The product manager should say: “We need the expected flow at the specified total head, for the exact voltage/frequency and construction we will sell.” The quality engineer should add: “Show the applicable test method, acceptance limits and sample/lot reference.” The packaging team should ask: “Which two numbers can be printed as separate maximum values, and what wording prevents customers from reading them as one simultaneous operating point?”
This is a stronger buying process than asking suppliers to promise that the pump is “high pressure” or “energy saving” without a common measurement basis.
When a curve is not enough
Even a sound Q–H curve cannot establish suitability for abrasive sand, seawater, chemical liquids, uninterrupted operation, a particular float-switch arrangement or destination-market electrical compliance. Those require separate construction, operating-limit and documentary checks. A performance curve also cannot justify claims about field service life or defect rates.
For a starting model and the evidence to request, see Pump Models, Quality Control, and OEM Projects.
FAQ
Can two pumps with the same maximum head perform differently? Yes. Their curve shapes and therefore their flows at the intended duty point may differ.
Should a buyer compare curves from different voltages directly? Only after confirming the curves correspond to the exact electrical variants and compatible test conditions.
Does a higher rated wattage guarantee more installed flow? No. Hydraulic design and the system operating point must be considered; wattage alone does not establish delivered flow or efficiency.