Understanding Pump Performance Charts

Have you ever found yourself in a situation where selecting the right pump becomes a nightmare? All you need is the pump that suits your application, so you start browsing around, but now you are faced with too many choices and charts that confuse you and won’t allow you to make a final decision. Not to worry, we are here to help!

This article is all about assisting you in understanding pump charts and their importance when choosing the right pump for your application:

• Pump size
• Pump performance
• Pump capacity
  • Suction lift
  • Fluid viscosity

Capacity charts and the Pump Size:

First of all, let’s take a look at the pump size. This step is crucial to determine how big or small a pump needs to be, to meet your application´s needs.

The desired flow rate and discharge pressure required can be achieved for many applications with different pump sizes.

Always choose your pump size considering your flow rate and discharge pressure. We recommend that you keep your pump working conditions in the middle of the chart’s coloured area.

Selecting the right pump size will result in high-quality performance with a reduced air consumption and a longer pump life.

Pump Performance and capacity charts

Now that you understand why the pump size is important, let’s take a look at the second chart you should be analyzing and why: The pump performance chart. This useful chart provides data regarding how a particular pump performs under certain conditions.

Here is a practical example using a real chart from our UP20 2” AODD pump:

Chart parameters:

• Y-axis (vertical) shows the discharge outlet pressure (bar-psi).  
• X-axis (horizontal) shows the flow rate (l/min – gal/min).
• Dotted line (grey) shows the pump air consumption (Nm³/h).
• Solid line (grey) shows the pump capacity curve.

To find the pump discharge pressure

1. Locate the desired flow rate along the horizontal axis (300 l/min).
2. Follow the vertical line up to the intersection with the pump capacity curve at the fixed air inlet pressure (5 bar).
3. Follow this point left and read the pump discharge pressure (Close to 3 bar).

To find the pump flow rate

1. Locate the desired discharge pressure drop on the vertical axis (6 bar).
2. Follow straight across to the intersection with the pump capacity curve (solid line) at the desired air inlet pressure (7 bar) feeding the pump.
3. Follow this line down and read the pump flow rate (140 l/min).
4. Air consumption in this case is 75 Nm3/h.

To find the air inlet pressure and air consumption

1. Locate the desired flow rate along the horizontal axis (400 l/min) and follow up.
2. Locate the known discharge pressure on the vertical axis (4 bar) and follow straight across.
3. The intersection of these two lines determines the pump operating point. Air inlet pressure should be set at 8 bar and the air consumption would be 185 Nm3 /h.

Pump Capacity

The pump’s effective capacity is determined by two factors: suction lift and fluid viscosity.

Suction Lift:

The first aspect to take into consideration is the SUCTION LIFT because pump effective capacity decreases when the suction lift increases.

In the following practical example, CHART A, you will find out how much the pump’s effective capacity can be reduced.

Example: 300 l/min theoretic delivery (water) and 4m suction lift

1. Locate the suction lift horizontal axis of CHART A (4 m).
2. Follow a vertical line upward, to the intersection with the curve on the chart.
3. Follow this point to the left and read the pump’s effective capacity (80%).
   • FLOW RATE = THEORETIC FLOW RATE X EFFECTIVE CAPACITY/100 Flow rate = 300 l/min x 0,8 = 240 l/min

Fluid Viscosity:

Viscosity is also a fundamental aspect when selecting a pump because it determines the fluid´s resistance to flow. This aspect is crucial because pump effective capacity decreases when the fluid viscosity increases.   If you wish to find out more about viscosity and density please visit this article.

To find out how much the pump’s effective capacity can be reduced depending on a fluid’s viscosity, let’s take a look at CHART B.

Example: 300 l/min theoretic delivery (water) and 6.000 mPas/cps fluid viscosity

1. Locate the fluid viscosity in mPas/cps along the bottom of chart B (6.000 mPas).
2. Follow a vertical line up to the intersection with the curve on the chart.
3. Follow this point to the left and read the effective pump’s capacity (60%).
4. FLOW RATE = THEORETIC FLOW RATE X EFFECTIVE CAPACITY/100 Flow rate = 300 l/min x 0,6 = 180 l/min

In a real-life scenario, the two previous examples will eventually combine into one:

If you are pumping a 6,000 mPas viscosity fluid with an installation suction lift of 4 m and a theoretic delivery (water) of 300 l/min, the real delivery would be:

FLOW RATE = THEORETIC FLOW RATE X EFFECTIVE CAPACITY DUE TO SUCTION LIFT/100 x EFFECTIVE CAPACITY DUE TO FLUID VISCOSITY/100 Flow rate = 300 l/min x 0,8 x 0,6 = 144 l/min