How to Read an AODD Pump Performance Curve: Complete Step-by-Step Guide

An AODD pump performance curve is the most important document for selecting the right AODD pump for your application and for verifying that an installed pump will deliver the required flow at your system conditions. Unlike a centrifugal pump single H-Q curve, an AODD pump performance chart contains multiple curves — typically one for each supply air pressure — and an additional air consumption axis. Reading it correctly takes approximately 5 minutes with this guide.

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What an AODD Pump Performance Curve Contains

Axis	What It Shows	Units	Position on Chart
X-axis (horizontal)	Flow rate — the volume of fluid delivered per unit time	LPM (litres per minute) or GPM	Bottom axis
Y-axis left (vertical left)	Discharge head — the pressure against which the pump discharges, expressed as head height	Metres of head (or bar, or PSI)	Left side axis
Y-axis right (vertical right)	Air consumption — the volume of compressed air consumed per unit time	Nm³/hr or SCFM	Right side axis
Multiple performance curves	Each curve = one specific supply air pressure. Higher supply pressure = higher curve (more head and more flow possible).	See legend on chart	Multiple lines across the chart area

Step 1 — Identify Your System's Two Known Values

Required flow rate (LPM): The volume of fluid that must be delivered per minute for your application.
System back-pressure (bar or metres of head): The total resistance the pump must overcome — includes static head, friction losses, and downstream pressure.

Step 2 — Locate Your Operating Point on the Chart

Metres of head = bar × 10.2 (for water; adjust for other fluid densities)

Step 3 — Identify the Minimum Air Supply Pressure

⚠ Never specify supply air pressure exactly at the curve that passes through your operating point. Always add at least 0.5–1 bar margin above the minimum curve. Air supply pressure can vary in plant distribution systems — a dip in header pressure below your specified minimum will stall the pump.

Step 4 — Read the Air Consumption at Your Operating Point

Step 5 — Check Efficiency — Are You at the Best Operating Point?

Operating Position on Curve	Flow Rate	Air Consumption per Litre Delivered	Efficiency Assessment
Far left of curve (very low flow, high head)	Low	High — slow strokes but high pressure per stroke	Poor efficiency — consider a smaller pump
Middle of curve (moderate flow, moderate head)	Moderate	Lowest air per litre — optimal efficiency	Best efficiency point — target this range
Far right of curve (high flow, low back-pressure)	High	Moderate — fast strokes but low pressure per stroke	Moderate efficiency — acceptable but maximum stroke rate increases wear
Above maximum curve (point not reachable)	N/A	N/A	Impossible operating point — increase supply or select larger pump

Step 6 — Verify NPSH and Suction Conditions

⚠ If your required suction lift exceeds the pump's capability at the required flow, you have two options: reduce the supply air pressure slightly to reduce flow rate and improve suction lift capability (moving left on the curve), or reposition the pump closer to the fluid source to reduce the actual suction lift.

How the AODD Curve Differs from a Centrifugal Pump Curve

Feature	AODD Pump Curve	Centrifugal Pump Curve
Number of curves	Multiple — one per supply air pressure	One (at rated motor speed) — or family for VFD operation
Flow at high back-pressure	Decreases as stroke rate slows — but pump continues operating	Decreases as operating point moves left on H-Q curve
Flow at low back-pressure	Increases as stroke rate increases (more strokes per minute)	Increases as operating point moves right on H-Q curve
Stall condition	Pump stops if back-pressure exceeds supply air pressure — safe, no damage	Pump runs at shutoff head — recirculates fluid, builds heat — damaging
Air / energy consumption axis	Yes — right-hand axis shows air use	No — efficiency shown as separate efficiency curve or not at all
Effect of higher supply pressure	Entire curve family shifts up and right — can develop more head and flow	Cannot increase head/flow without increasing motor speed (VFD required)

Worked Example — Reading a Complete AODD Pump Curve

Application: chemical transfer, required flow 80 LPM, system back-pressure 3 bar (30.6 metres head), suction lift 2 metres.

Plot the operating point: 80 LPM on X-axis, 30.6 m on left Y-axis. Mark the intersection.
Identify required curve: the operating point falls between the 4 bar and 6 bar supply pressure curves. Minimum supply pressure is just above 4 bar — specify 6 bar with a regulator set to 5 bar for margin.
Read air consumption: at 80 LPM flow on the 5-bar curve, the air consumption axis (right Y-axis) reads approximately 18 Nm³/hr.
Verify suction lift: the suction lift curve at 5 bar supply and 80 LPM shows a maximum suction lift of 4.5 metres. Your installation requires 2 metres — within capability.
Check efficiency: the operating point is in the middle third of the 5 bar curve — good efficiency zone.
Calculate annual air cost: 18 Nm³/hr × 8 hr/day × 300 days × Rs. 2.50/Nm³ = Rs. 1,08,000/year.

FAQs — Reading AODD Pump Performance Curves

Q: My operating point falls below all the curves on the chart. What does this mean?

It means even the lowest supply air pressure shown on the chart (typically 2 bar) can deliver your required flow at your back-pressure with margin to spare. You may be able to use a smaller pump model — check if a smaller size's performance chart covers your operating point. Running a pump significantly larger than needed wastes air, increases noise, and increases diaphragm wear rate.

Q: My operating point is above the highest curve on the chart. What do I do?

You cannot achieve the required operating point with this pump at the maximum rated supply pressure. Options: increase supply pressure if the pump is rated for it (check maximum rated pressure in the datasheet); or select a larger pump model whose performance curve covers your operating point.

Q: Why does the AODD pump curve show multiple lines instead of one?

Because AODD pump performance changes with supply air pressure — unlike a centrifugal pump at fixed motor speed, the AODD pump's pressure and flow capability varies continuously with the supply air pressure. Each line on the chart represents one specific supply air pressure, giving you a family of operating possibilities. The air regulator on the supply line lets you select which curve to operate on.

Q: What happens at the end of the curve (zero flow)?

At zero flow (fully closed discharge), the AODD pump stalls — the diaphragm cannot move against the back-pressure because it equals the supply air pressure. The pump stops safely and restarts automatically when discharge pressure drops. This is the safe dead-head condition — no damage to the pump, unlike the centrifugal pump's overheating dead-head condition.

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Unique Pump Systems manufactures air operated double diaphragm pump in the full range of sizes and materials. Performance curves are available for all pump models on request. Contact our technical team for operating point verification and pump sizing support.

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How to Read an AODD Pump Curve