Maintaining pumps saves energy

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Pumping is a major expense in broadacre farming and even small savings achieved through pump maintenance can have a noticeable impact in reducing overall energy costs.

Pump wear comes from excessive starting and stopping, pump cavitation and erosion from particulate material.

In the absence of regular maintenance, pump performance deteriorates steadily. Typically, a drop in efficiency of between five and 15 percent occurs after 10 years of operation.

When pumps are maintained to keep their efficiency close to its original point, significant energy savings can be made.

A pump overhaul may include: replacement of wear rings, seals, bearings and if worn, the impeller; cleaning of internals; blast cleaning of casing externals; and the application of new epoxy coating.

Technical explanation

When a pump wears, it tends to generate less flow and head, requiring more power to achieve the desired output. 

Effects of pump wear
Figure 1: The effects of pump wear
UK Department of Environment

The typical trend of efficiency deterioration over the life of a pump is shown in Figure 2. 

Pump efficiency deterioration
Figure 2: Pump efficiency deterioration over time. A sharp drop in efficiency occurs in the first few years.
UK Department of Environment

Studies have found that:

  • much of the wear occurs in the first few years,
  • after about 10 years the wear tends to level out,
  • the overall drop in efficiency for an unmaintained pump can be around 10 to 12.5 percent,
  • an unmaintained pump can reach catastrophic failure after around 20 years’ service, and
  • periodically maintaining the pump can return its efficiency to a level close to that of a new pump (UK Department of Environment, 1998).

Worked example

After 10 years of service, the efficiency of a worn pump has deteriorated by 10 percent. The duty point of the pump, when new, was 350 L/min and 30 m, but now it has changed to 340 L/min and 28 m. The effect is illustrated in the diagram below:

Best efficiency point
Figure 3: The effect of a worn pump on head and flow performance.
NSW Farmers


Where:The impact on power consumption is: 

The power consumtion before the overhaul is given by:

  = 

And assuming the pump efficiency of the new pump is 80 percent and the motor efficiency is 92 percent, the power consumption after the overhaul is given by:

 = 

Therefore, our power consumption decreases by 3.3 percent following the overhaul.

Key factors when evaluating quotes

Compare the actual pumping efficiency with the original efficiency, as given in the manufacturer’s specifications.

Measure the efficiency before and after the overhaul of your pump to determine the improvement in efficiency.

Determine the optimal maintenance cycle by looking at the time between the last pump overhaul and the pump’s efficiency reaching a set low limit. These parameters will allow you to evaluate the cost/benefit of each overhaul.

Most pump parts are generally standard-designed and in terms of key parameters, there is little to differentiate them. However, there are few points to consider:

  • When replacing a standard impeller, look for high-efficiency designs to improve pumping efficiency. If the pump is oversized, select an impeller with a smaller diameter to match the specific system requirements and reduce energy consumption.
  •  When replacing metallic wear rings, consider using non-metallic ones (e.g. those made of thermoplastic composite material) which reduce friction and flow recirculation from the discharge side of the impeller back to the suction side, thus improving pump efficiency by typically two to four percent. These wear rings are more expensive than metallic ones, but paybacks are generally good (<3 yrs), particularly for pumps with high maintenance costs.

If your pump’s internal surfaces are heavily eroded and/or corroded, consider applying a smooth epoxy coating, which can improve the efficiency of the pump by one to five percent and provides better protection against corrosion and erosion, extending pump life and reducing maintenance costs.

 

worn pump parts
Figure 4: Generally, pump running costs are around $25 per megalitre (ML) for normal medium-pressure sprinklers and $35/ML for high-pressure (90 psi) sprinklers – but if damaged or worn, the pump could cost you an additional $10/ML
Department of primary industry

Further Information

Sustainability Victoria - Energy Efficiency Best Practice Guide: Pumping Systems.

Preventative maintenance for pumping systems

References

Department of Primary Industries, n.d. Worn parts help you part with your money. [Online]

Natural Resources Management in Northern Tasmania, 2009. Future farming fact sheets: Farm and irrigation energy efficiency. [Online]

Pledger, J., 2001. Improving pump performance & efficiency with composite wear components. World Pumps: The international journal for pump users, Issue 420.

UK Department of Environment, 1998. Good practice guide 249: Energy savings in industrial water pumping systems. s.l.:s.n.


This content was produced with assistance from Energetics
www.energetics.com.au

 

Energy, Water, Cropping, Energy

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