Columnist Jim Elsey gives more examples of problems pumps might face and how a good salesperson would handle them.
by Jim Elsey
December 5, 2019

Editor’s Note: This is a continuation of Jim Elsey’s column from the November 2019 issue of Pumps & Systems titled “Wanted: Great Pump Salespeople.”

The myriad list of things that can go wrong with pumps in the field is long. In the confines of this column, I can list only a few examples. For today, we will assume all applications are centrifugal pumps.

Rather than explain one or two examples in detail, I thought it may be more interesting to provide a list of problem-based scenarios and the solution. These are all cases I have worked on in the last few years. Most examples will have more than one correct answer.

What’s Wrong with These Applications?

Problem: On a self-primer lift application the new pump is running erratically and performance is poor. This should be an easy application because the lift is only 10 feet on clean water.

Solution: In this frequent issue, the temperature of the water was ignored. The temperature of 160 F resulted in a (negative) vapor pressure of almost 11 feet, which when combined with the lift of 10 feet and the friction loss negated the positive contribution of the ambient pressure in the net positive suction head available (NPSHa) formula. The pump will cavitate, but it won’t lift the water.

Another common issue is an air leak in the suction line. People are surprised that ambient air can leak in without water leaking out. Wrap the suspected leak area with plastic and/or duct tape as a temporary measure to find and confirm the leak location.

Next on the list is submergence. With an insufficient height of liquid above the suction pipe entrance, air is introduced into the line. We assume the suction line, foot valve or strainer is not clogged in all of these cases.

Problem: A few miles away from the previous problem is yet another new self-primer pump application. The pump is attempting to pump treated water at ambient temperature from a wastewater treatment tank to a retention pond. The pump will not prime on a simple lift application of 5 feet.

Solution: The customer checked the 10 most common reasons for self-primers not to prime, but to no avail (see my article on this in the September 2016 issue). Turns out there is an 11th reason as a result of solving this issue. Self-primers are not well suited to pump water treated with surfactants. The surfactant caused the water to disassociate and foam in the priming chamber. The issue was solved by using a submersible pump.

Problem: The customer purchased a beautiful six-stage BB3 pump, driven by a foot-mounted condensing steam turbine. The pump is designed for continuous service on 450 F hydrocarbons. During the first six months of operation, the pump bearings have failed three times. The radial bearings are a fluid film type and the axial bearings are tilting pad thrust shoes. The customer is using a high-quality, mineral-based hydraulic oil in the bearings.

Solution: For this application, the customer should be using a turbine oil, not a hydraulic oil. Further, they should be using a synthetic based oil or a blend for this temperature range. The turbine oil will at a minimum contain rust and oxidation inhibitors, which the hydraulic oil does not.

Problem: The customer needs to increase throughput in the facility and added a third horizontal split case pump to the cooling water system. All three pumps are the same size, model and hydraulic rating (exact same size impellers). When the third pump was added, the overall flow rate only increased by a small percentage. The bearings subsequently developed issues due to excessive heat, so maintenance ran plant service water on the outside of the housings to keep them cool.

Solution: Bottom line issue in this case is that the pipe is too small to handle the flow rate. Pumps will operate where the system tells them to run. Adding the third pump just forced each pump to run back to the left on its operating curve and far away from the best efficiency point (BEP). In this operating range the pump dynamics place an increasing load on the bearings (see my March 2016 article for more details on the subject).

Running water on the outside of a hot bearing housing just makes the situation worse. The hot inner bearing is trying to expand due to the higher (hot) temperatures. The outer surfaces are contracting due to the lower temperatures offered by the cooling water. The difference puts the bearing in a mechanical bind and shortens the life.

Problem: A simple single-stage pump in a flooded suction application on ambient temperature water. The pump ran fine for several years, but now suddenly performs at about 65 to 70 percent of expected performance and the motor runs hot with increased vibrations.

Solution: An issue you will not frequently encounter, but these symptoms are classic for a motor that is single phasing. That is, one of the three phases has shorted out, and the motor is operating on two phases.

Problem: A customer starts up a new pump and within an hour the operator calls the supplier because the bearings are running hot and they need to shut down and perhaps replace the pump.