Pump flow and head belong together at the required duty point. Maximum flow and maximum head listed separately do not establish the flow available at the head your system needs. Request the offered pump’s curve and the defined system requirement.
This guide addresses a centrifugal-pump curve in a liquid-circulation proposal. If a cutting-machine offer includes such a circuit, use the questions below to review its documentation. They do not identify a pump fitted to a JiurunCut model.
Read one pair, then its conditions
- Flow: how much liquid is required per unit of time?
- Head: what head is required at that same flow?
- Conditions: which liquid and offered pump configuration does the curve cover?
On this page
1. Keep pump flow and head on the same curve
Grundfos’s pump-curve overview describes the relationship between flow Q and head H. Its curve-reading lesson explains the intersection of a pump’s performance curve and the system characteristics. That intersection identifies the duty point.
Ask the system designer to identify the required flow-and-head pair. Then ask the supplier to locate it on the applicable offered curve. A headline maximum does not answer this paired question.
A fictional curve with three stated points
For a teaching example, assume the following three points belong to one invented centrifugal-pump curve at a fixed configuration. The values are invented; they are not measurements, a product recommendation or an operating procedure.
| Assumed flow Q | Head H at that same point |
|---|---|
| 0 litres per minute | 12 metres |
| 20 litres per minute | 8 metres |
| 40 litres per minute | 0 metres |
The example has a 12 m head value at zero flow and a 40 L/min flow value at zero head. Combining the two into “40 L/min at 12 m” creates a fourth pair that the stated points do not support.
By contrast, 20 L/min at 8 m is an explicitly stated point in the fictional data. That still does not establish a real system’s duty point, efficiency or complete pump suitability. It simply keeps the two coordinates together.
The three points are not a complete curve. Do not estimate every intermediate point or allowable operating condition from this short table. Request the manufacturer’s applicable curve and the responsible system review for the actual equipment.
When two quotations use different units, align the units before comparing them. In this example, 20 L/min equals 1.2 m³/h: 20 × 60 ÷ 1,000 = 1.2. The conversion changes the notation while retaining the same volume per time.
2. Read head and pressure with the liquid identified
Head is expressed as a length. Pressure is expressed in pressure units. Do not compare an entry in metres directly with an entry in bar as if they were the same numerical quantity.
Grundfos gives the conversion p = ρ × g × H, where ρ is liquid density, g is gravitational acceleration and H is head. Keep the density basis visible when converting between head and pressure.
An original stated-density calculation
Assume a fictional liquid density of exactly 1,000 kg/m³ and g = 9.81 m/s² for this calculation. At 8 m of head, the corresponding pressure difference is 1,000 × 9.81 × 8 = 78,480 Pa.
Since 1 kPa equals 1,000 Pa and 1 bar equals 100,000 Pa, that result is 78.48 kPa or 0.7848 bar. It applies to the assumptions just stated. It is not a measured coolant pressure or an approved pressure setting.
A different density changes the pressure difference corresponding to the same head. Keep the actual fluid requirement in the proposal, and let the responsible designer use its applicable properties. Do not replace that requirement with this teaching assumption.
Also ask what pressure entry the quote describes. A pump-generated pressure difference and a pressure reading at a named connection should be identified clearly. The record should say where and under what stated conditions a reading is taken.
For pump flow and head comparisons, keep the unit conversion beside the paired duty values. This makes it easier to review two proposals without silently changing the intended flow, head or fluid basis.
3. Verify pump flow and head for the supplied configuration
Ask for the offered pump reference and the configuration to which the curve applies. Identify the documented speed or control mode and any other configuration stated on the curve. Keep its revision with the quotation.
If an offer changes a pump or its configuration, ask for the corresponding updated curve and review. A retained maximum-flow label does not show that the required duty pair is unchanged.
Grundfos’s lesson distinguishes the flow-head, efficiency, power and NPSH curves. A flow-head point alone does not complete the selection. Ask the responsible team to review the additional information needed for the application.
Keep the actual liquid and system requirements explicit. If the proposal covers a circulating liquid, identify it separately from compressed air, mist lubrication or a hydraulic actuation circuit. Our pneumatic and hydraulic saw guide explains why a machine’s individual functions should be named separately.
List the supplied scope with the circuit drawing: pump, associated components and agreed documentation. State which items are supplied elsewhere. This lets the purchasing team compare complete offers using the same application definition.
At handover, agree how the responsible team will record the actual flow and relevant pressure or head information. Keep the instrument identities and measurement locations linked to the record. A photograph of the machine running does not provide those readings.
Ask how any observed result will be compared with the approved requirement. Use the factory-acceptance review guide to organize the agreed evidence and responsibilities. Retain the application-specific methods in the supplied documentation.
Buyer questions about pump flow and head
Can I combine the maximum flow and maximum head?
No. Ask for the flow available at the required head on the applicable curve. The fictional example shows why separately listed maxima do not establish that pair.
Does 8 m always mean 0.7848 bar?
No. That conversion used the explicitly assumed density of 1,000 kg/m³ and g = 9.81 m/s². Retain the actual fluid basis.
Does matching one duty pair approve the complete installation?
No. The offered configuration and application need the responsible review, including the relevant additional curves and supplied system documentation.
Keep the cutting inquiry and utility scope together
Send JiurunCut the profile drawing, cut list and required utility scope. If a circulation circuit is part of the project, identify the approved pump flow and head requirement and request the applicable offered documentation.