Water pumps are a common application of electric motors. Keeping in mind that this course was designed with water-company employees in mind, this video is one of the most important portions of the class. David alludes to the existence of non-submersible pumps, but the people who were signed up for the course consistently have to work with submersible pumps. Troubleshooting of non-submersible pumps is typically less difficult, and the information provided in this lesson should be still be applicable.
Video Synopsis
Pump Components: A pump is a standard electric motor with an impeller attached and added components to protect it from water. (An impeller is the rotating part of the pump that moves water or other fluid by rotation.) Mechanical seals, located in an oil chamber, are used to keep water from entering the motor and damaging the pump. Standard electric motor components including the coil, stator, shaft, and bearings are also part of a pump motor. More aggressive cooling systems and moisture detection systems may also be included in water pumps.
Two Types of Pumps: A common question on certification exams involves the difference between centrifugal pumps and positive displacement pumps. A centrifugal pump will only operate if it can move fluid without building up excessive pressure. If something blocks the flow of fluid (for example, by closing a valve, which David calls “dead-heading”), a centrifugal pump will stop functioning before the pressure is great enough to damage the pump motor. On the other hand, a positive displacement pump will continue to build pressure regardless of its environment; a positive displacement pump will readily build enough pressure destroy itself or to rupture a line in the system its attached to.
Types of Centrifugal Pumps: Several different types of centrifugal pumps are noted in the workbook. These include, but are not limited to the following: inline pumps, close-coupled pumps, submersible pumps, vertical immersion sump pumps, vertical turbine double-casing pumps, center-hung double-suction split-case pumps, multistage pumps, axially split two-stage pumps, radial split multistage barrel pumps, centerline-mounted pumps, multistage axial split-case pumps, and split-suction pumps. Illustrations of these centrifugal pumps can be found on page 9 of the workbook.
Types of Positive Displacement Pumps: Likewise, there are many types of positive displacement pumps. Some examples of these are: peristaltic pumps, gear pumps, screw pumps, vane pumps, rotary lobe pumps, progressive cavity pumps, piston pumps, diaphragm pumps, and hydro-static pumps. Illustrations of these positive displacement pumps can be found on page 10 of the workbook.
Seals: Seals are a common point of failure in electric pumps. If a pump is not being cooled effectively, seals may fail more quickly than normal. If the same seal repeatedly needs to be replaced in a production environment, it is indicative of an underlying problem somewhere else in the system. David discusses a situation in further detail about how an operator-caused error resulted in the need for the repeated replacement of seals on a pump that he had been troubleshooting. Eventually, his customer discovered that an equipment operator was leaving pressure on the pump while on break, and this undue pressure was causing the seals to fail.