Quick Facts...

• Most pumping systems have excessive operating costs because they use more energy (power or fuel) than they should.
• Pumping system performance can be evaluated remotely and continually with the Watchman System™ to determine if changes are needed.
• Some problems can be corrected with simple adjustments while others require expensive repairs.

Rising energy costs have increased the cost of water pumping to the point that many are finding it only marginally profitable and/or sustainable.

Fortunately, pumping costs are an item over which pumpers can have some degree of control. Pumping costs often are higher than they need be for two reasons: 1) more water is pumped than is necessary, and/or 2) the pumping plant operates inefficiently. This article will only the second problem: inefficient pumps.

Common Causes and Remedies

With the Watchman System™ water system operators can determine which pumps are operating to the highest efficiency in “Real Time.”

Field testing programs have shown that overall or "wire-to-water" plant efficiencies for electrically driven pumps average less than 50 percent, as compared to a realistically achievable efficiency of 67 percent. This implies that 25 percent of the electrical energy used for pumping is wasted due to poor pumping plant efficiencies alone. Therefore, energy costs can be significantly reduced by raising pumping plant efficiencies from present average levels to potential higher efficiencies.

With the Watchman System™ water system operators can:

• Determine which pumps are operating to the highest efficiency in “Real Time.”
• Make system changes immediately with any Internet-connected computer
• Predict system problems for planning “in-field” repairs to prevent downtime
• View Historical Data to schedule routine maintenance procedures

There are many reasons for poor pumping plant efficiency. Some of the more common causes of unsatisfactory performance and their remedies are as follows:

1. Impellers out of adjustment are the easiest and least expensive problem to correct. Both pumping rates and efficiency are reduced because energy is used to pump water that is bypassed around the impellers instead of being pumped into the system. Impeller adjustment is especially critical with semi-open impeller pumps. Impellers may be out of adjustment because of improper initial adjustment or because of wear. To avoid pump damage, only professional pump technicians should attempt to make impeller adjustments.
2. Pump bowls improperly designed is a common explanation for poor pumping plant efficiency. Overestimating well yield frequently results from the inadequate development of a well after drilling. In these conditions, a pump is required to operate at some point other than the Best Efficiency Point for which it was designed. In some cases, a pump supplier may recommend oversized pump bowls in order to require fewer stages, to reduce initial cost. Furthermore, declining water tables in some areas have reduced well yields. In these conditions, a pump is forced to operate at a lower flow rate and higher lift than that for which it was designed. If for any of these reasons the pump capacity does not fit the well characteristics, high pumping plant efficiency can be achieved only by replacing the bowls with new bowls that meet the well requirements.
3. Damaged impellers also will result in poor performance. Three common causes of impeller damage are cavitations, sand pumping and improper impeller adjustment. Sometimes only the impellers need to be changed, but more often the permanent solution is to replace the entire bowl assembly. If this is done, it is likely that a different model of pump bowls should be used to fit present well conditions.
4. Incorrect power unit selection is another major cause of low efficiency. This is much more important for engines than for electric motors. While the efficiency of electric motors does not vary greatly with loading, it should be noted that over-loaded motors have shorter lives, are less dependable and are more expensive to maintain. On the other hand, because of graduated energy costs, under loaded motors often increase the cost per kilowatt of power used. Incorrect engine selection is a major cause of low efficiencies among diesel and/or natural gas pumping plants. Operating speeds of the smaller engines are increased so that they will produce adequate power. As a result, they can have excessive wear and low fuel economy.
5. Failure to perform required maintenance, including tune-ups, is often a cause of low efficiency in engine-driven pumping plants. Electric motor efficiency can be improved by using the newer high or premium efficiency motors. Finally, a change in operating conditions from those for which a pumping plant was designed will result in a drop in efficiency. Three common situations that result in increased pumping lifts or pressures are a drop in water table elevation, changing hydraulic conditions from original design. I.e. adding more pipelines, higher flowing connections and/or leaking in the distribution system.

Field Pump Evaluation

Field evaluation of electrical pumping plant performance is a valuable tool to asses existing pumping plant efficiency. Internal combustion engine driven plants can be tested as well. A private testing contractor and/or a professional pump contractor are trained and equipped to provide a Overall Pumping Plant Test.

A field pump evaluation involves measuring several operating characteristics of the pump. These include:

• depth to static water level
• depth to water level during pumping,
• pump discharge pressure,
• pump flow rate, and
• Rate of electrical energy or fuel consumption.

From these measurements, both the water horsepower, and rate of useful work done by the pump, and input horsepower equivalent, or rate of energy used by the motor or engine, are calculated. Overall pumping plant efficiency is the water horsepower divided by the input horsepower equivalent.

More in the next article on evaluating replacement costs options.