A Step-by-Step Guide to Reading Pump Performance Curves

〔How to Estimate Pump Flow Rate Based on Known Conditions?〕

〔How to Set Installation and Driving Conditions of My Pump Based on Flow Rate?〕

Understanding pump performance curves can solve these problems for you!

The performance curve of an air-operated diaphragm pump illustrates the pump's performance data under different environmental and operating conditions. The main performance parameters include flow rate, head (negative pressure), and inlet air pressure. Follow these steps to understand the performance curve.

1. Understanding the Structure of the Performance Curve:

   The performance curve is displayed in an XY chart format, with the horizontal axis (X-axis) representing the flow rate in liters per minute (LPM) or gallons per minute (GPM). The vertical axis (Y-axis) represents the head or working pressure (negative pressure), with head measured in meters or feet and working pressure in Bar or psi. The solid curves in the chart represent different driving air pressures in Bar, while the dashed lines represent the air consumption of the pump under those conditions, measured in liters per minute (LPM).

2. Setting Known Conditions:

   Based on the set head (working pressure) and inlet air pressure, you can estimate the flow rate of the pump model.

3. Choosing the Inlet Air Pressure Curve:

   The performance curve chart marks curves for different inlet air pressures. Choose the curve for your set condition, such as the 1 Bar, 3 Bar, or 5 Bar curve.

4. Finding the Corresponding Flow Rate from the Set Conditions:

   Find the set head (working pressure) position on the Y-axis, then extend horizontally towards the X-axis until it intersects with the chosen inlet air pressure curve. From the intersection point, extend vertically downwards to find the corresponding flow rate on the X-axis.

   For example, if you run the pump at 5 Bar inlet air pressure and want to know the flow rate at an outlet head of 10 meters, find the 5 Bar curve and the intersection point at 10 meters head, then extend vertically downwards from the intersection point to find the corresponding flow rate.

5. Cross-Referencing:

   The performance curve also provides air consumption range curves, which can be cross-referenced to find the most efficient operating conditions.

6. Determining the Appropriate Pump Size:

   To ensure that the air-operated diaphragm pump operates normally and achieves maximum efficiency and lifespan, it's recommended to use a stable operating pressure of 1.5-3.5 Bar. Lower pressure reduces friction between the sealing ring and the mating parts, extending the pump's lifespan and durability.

   For example, if the required flow rate is 40 LPM, a 1/2-inch pump's maximum flow rate is 48 LPM, and a 3/4-inch pump's maximum flow rate is 85 LPM. In this case, choosing the 3/4-inch diaphragm pump is preferable. Although the 1/2-inch pump can achieve the required flow rate, it would need a higher operating pressure, affecting the pump's lifespan and efficiency. Therefore, a larger size air-operated diaphragm pump is recommended.

Note: The performance curve is measured under conditions of water, low negative pressure, and low pipeline resistance. In actual situations, factors such as fluid density, viscosity, pipeline resistance, pipe diameter, valves, air supply distance, and air compressor specifications must be considered, as they all affect the actual outlet flow rate and pressure values.

Example 1: According to the performance curve, what is the flow rate at 5 Bar air supply pressure and 20 meters head?

1. Find the 5 Bar inlet air pressure curve.
2. On the Y-axis, find the 20-meter head position and move horizontally along the X-axis until it intersects with the 5 Bar curve.
3. From the intersection point, move vertically downwards to find the corresponding estimated flow rate of 33 LPM.

Example 2: I need at least 20 LPM flow rate at an approximate head of 20 meters. What is the minimum inlet air pressure required?

1. Find the 20 LPM flow rate position on the X-axis and the 20-meter head position on the Y-axis.
2. Move horizontally right from the 20-meter head position and vertically up from the 20 LPM flow rate position to find the intersection point.
3. According to the intersection point, find the nearest inlet air pressure curve above that point, or which curve the point falls on. The chart shows the intersection point falls on the 3 Bar curve, indicating the required input air supply pressure is at least 3 Bar.

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