How to Read a Pump Performance Curve (H-Q Curve)

The short answer: a pump performance curve (also called H-Q curve) is a graph that shows how much water a pump delivers at any given head. The X-axis is flow (m³/h), the Y-axis is head (m). Every point on the downward-sloping line is a real operating point. Find where your needed head and flow intersect on the curve — if the point is below the curve, the pump can do the job.

Every pump model we publish has a performance curve on its product page. This guide teaches you how to read them.

Anatomy of a curve

Here’s what you’ll see on a typical pump chart:

Head (m)
  ↑
  │╲
  │  ╲  ← Pump curve (H-Q)
  │    ╲
  │      ╲
  │        ╲
  │          ╲
  │            ╲
  └──────────────→ Flow (m³/h)

• Top-left (zero flow): This is the shut-off head — the maximum pressure the pump can produce when no water is flowing. This is the “Max Head” number in the spec sheet.
• Bottom-right (zero head): This is the maximum flow — the most water the pump can move when there’s no elevation to push against. This is the “Max Flow” number.
• In between: every point on the curve represents a valid combination of head and flow. As you demand more flow, the head drops.

How to use the curve for your project

Step 1: Calculate your required head

Your required head = well depth + drawdown + pipe friction + delivery height. See our head calculation guide for details.

Step 2: Calculate your required flow

Your required flow = daily water need ÷ sun hours. Example: 10 m³/day ÷ 6 hours = 1.7 m³/h.

Step 3: Find your operating point on the chart

Plot your required head (Y-axis) and required flow (X-axis) on the chart. This is your operating point — the dot where your needs intersect.

Step 4: Check if the curve passes above your operating point

• ✅ If the curve is above your operating point → the pump can deliver your required flow at your required head.
• ❌ If the curve is below your operating point → the pump is too weak. Choose a larger model.
• ⚠️ If your point is very close to the top-left (near shut-off head) → the pump will be running at very low efficiency and deliver minimal water. Choose a model whose curve passes comfortably above your point.

The golden rule: operate at 60–80% of max head

A pump running at its maximum rated head is at the extreme edge of its curve — flow is minimal, efficiency is terrible, and the motor works the hardest. This is the worst place to operate.

The sweet spot is 60–80% of the rated max head. At this point:

• Flow is 40–70% of maximum
• Efficiency is near the Best Efficiency Point (BEP)
• Motor stress is minimal
• Pump lifespan is maximized

Example: if a pump has a rated max head of 100m, your operating head should ideally be 60–80m. At 60m, you’ll get significantly more water than at 95m, and the pump will last much longer.

Understanding the “rated” vs “maximum” confusion

Many buyers look at “Max Head = 100m” and think “my well is 90m, so this pump is fine.” This is wrong.

• Max Head = shut-off head = zero flow. The pump produces pressure but no water.
• Working head = the head where you actually operate = 60-80% of max.

At 90m head on a 100m-rated pump, you’re operating at 90% of max — the pump will deliver a trickle of water and run at the edge of its capability. Choose a pump rated for at least 1.2× your actual head requirement.

How to compare two pumps using curves

When comparing models, don’t just look at the max head and max flow numbers. Look at the curves:

1. Plot your operating point on both charts.
2. Which curve passes further above your point? That pump has more “headroom” and will operate more efficiently.
3. Which curve is closer to the BEP at your operating point? That pump will use less energy and last longer.

A pump with “lower” max numbers but a curve that passes well above your operating point is often a better choice than a pump with “higher” max numbers where your point is near the curve’s edge.

Reading curves on solar pumps: the variable-speed reality

A solar pump doesn’t have a single fixed operating point like a grid pump at constant 50Hz. The MPPT controller continuously adjusts pump speed as sunlight changes, so the pump moves along the family of curves through the day: slower with less flow in the morning and evening, at rated speed around midday, and slower again during cloud. Size for your peak requirement — the flow you need in the sunniest hours — and let a storage tank absorb the slower hours. A pump whose curve only just passes your operating point loses the morning and evening production that headroom would have bought, which is why the 60-80% rule matters even more for solar than for grid pumps.

Multi-stage pumps (the 3DPC/4DPC series, for example) have steeper curves than single-stage pumps — flow changes less as head changes, which suits deep wells with a fairly fixed head. My sizing tool plots your operating point on the real curves.

Reading our product page curves

On each product page, you’ll find:

• A curve chart with all models in the series overlaid
• Your operating point (if you’ve used the sizing tool) shown as a green dot
• The spec window (if set) shown as an orange shaded area
• Model labels on the curves for identification

The curves on our charts are approximate — computed from the rated max head and max flow using the standard centrifugal pump formula: H(Q) = H_max × (1 - (Q/Q_max)^1.8). Actual curves vary slightly by manufacturing tolerances and water conditions.

Quick reference: what the numbers mean

Ready to find the right pump? Use the sizing tool — enter your well depth and water need, and see the curves with your operating point plotted automatically. Or message me on WhatsApp with your specs and I’ll read the curves for you.