The biggest expense with centrifugal pumps is not the initial setup cost of the pump itself, it's the cost of electricity over time. Energy is an intangible cost, which can have a big impact on your return on investment (ROI). If your pump is drawing too much power, which means it is running far from its best efficiency point, then the cost of operating that pump inefficiently can be much higher than the initial cost of the pump.
The first thing you need to do is measure the power consumed by the pump and check it against the pump's performance curve to see if it's operating efficiently. The pump curve specifies how much power the pump is using at its correct flow and pressure. You can then calculate potential energy savings by addressing these issues. Here are five reasons why your pump might be drawing too much power:
1. Pump is too small or too large for its application
Sometimes pump sizes are specified in anticipation of future needs. Many pumps are oversized because of safety factors that were added at the time the pump was selected. This means that throttling is a normal condition in most plants, resulting in the pump running on the left hand side of its curve. A pump may also be sized for maximum operating conditions, but the plant does not run anywhere near that point most of the time.
If the pump size is not right for its application, the pump will run less efficiently in its operating range and use more power. Check and resize your pump for best results.
2. Viscosity and gravity are different from specification
If the fluid viscosity that is pumped is thicker than what was originally specified, it will take more energy to meet the pump's application needs. Viscosity may change with agitation, like when cream becomes butter, or through changes in temperature (some viscosities change with low temperature, some with high temperature). The pump motor may also be sized for a low specific gravity fluid, but water is used to flush or test lines. Gravity of the fluid can also increase. You may need to resize the pump in order for it to run efficiently in the application, or a different pump technology may need to be used.
3. Internal clearances incorrectly set
A pump's internal clearances are critical for its effective operation. If clearances are not tight enough and somewhat open, the pump will lose efficiency, as fluid will not move through the pump as intended.
If clearances are too tight, the pump's internal components may rub against one another, causing drag, which requires extra energy for operation. This rubbing may eventually cause damage to the internal components of the pump, causing the pump to become less efficient and over time, requiring either parts or the entire pump to be replaced.
Make sure you follow the manufacturer's manual to set pump clearances correctly.
4. Incorrect Rotation
If your pump is rotating in the wrong (opposite) direction, it will not perform as designed, and will use much more energy. The pump will still pump fluid, but at a fraction of the flow and head that it should be, as shown in the performance curve. Most impellers are not designed to run in the opposite of their intended direction, so ensure correct installation of power to the drive unit to ensure the proper rotation of the pump.
5. Packing gland has been overtightened
The packing gland on a pump is often tightened so the packing doesn't "leak". However, the nature of packing requires the packing to leak to keep the seal area properly lubricated. Another issue that can occur when the packing gland is too tight is that the packing is over-compressed on the shaft, causing resistance on the shaft that uses more power. Ensure you follow the instructions on the manual and don't overtighten the packing gland. This will ensure the packing has the right compression and does take additional energy.
Ultimately, it's important to identify if one or more pumps are drawing too much power as this can be a great way to reduce inefficiencies and save on energy and costs.
If you have any questions, please call our toll-free number 1-800- 367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.