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A centrifugal pump is a machine that uses a motor to transport fluids by the conversion of centrifugal force. The fluid enters an impeller that rotates inside a casing and flows radially outward into a volute chamber or diffuser, from which it exits. The rotational kinetic energy imparted to the liquid by the propeller is converted to the hydrodynamic energy of the fluid flow.
Centrifugal pumps are commonly used in mining, agriculture, sewage, petroleum, power generation plants, petrochemical pumping, and many other industries. Centrifugal pumps are unique because of their abrasive solution compatibility, high flow rate capabilities, relatively simple engineering, and mixing potential.
Centrifugal pumps live a hard life and while they’re often heavy duty and made to last for years, there are a number of environmental and workplace factors that can take a toll on them. From time to time, there can be noticeable changes in the performance of the pumps, and good troubleshooting procedures can help address the issues and keep the pumps up and running properly.
Here are some common problems with centrifugal pumps:
This can be caused by a number of factors. It could be a change in pumped media viscosity or a fault in the direction of shaft rotation. Loss of flow is a common problem if the pump stores mineral-based oil, which changes viscosity with temperature fluctuations. Fluids that are thicker than normal could result in a higher power requirement and reduced performance. If the fluid if a strong acid or base, there could be a change in dilution gravity, which may affect the power curve.
You need to verify the property of the pumpage to determine if it’s the problems. Tests for the temperature of the fluid, viscosity, and specific gravity are necessary in this case. Check seal viscosity limitations and use standard conversion formulas and charts to determine if the pumpage is affecting the performance of the pump.
If the fluid properties are normal, the problem may be the flow of liquid in the system to which the centrifugal pump is connected. A low-flow condition typically indicates a restriction in the suction line or the discharge line. If the suction line is restricted, cavitation will likely occur. Other possibilities of low flow are that the discharge static head is too high or the suction head is too low.
Conversely, a low-head condition indicates that the flow is too high. It could also be a problem with system leaks that cause incorrect flow of fluid. A failed check valve that allows the fluid to move backward or a diverter valve allows to flow would result in low head (low line pressure) and too much flow. Reduced discharge pressure could also result in loss of flow. The problem could be that the pump is worn so it’s worth getting it checked and replaced.
When considering flow and head as a possible issue, it’s important to correctly operate on the pump’s curve. You may also want to check if the wrong pump is being used either because of mistaken installation or improper design.
This is a situation where the pump loses its suction power due to insufficient inlet pressure. This could be caused by cavitation, an increase in fluid viscosity, or clogged suction inlets. Signs of suction problems include increases in vibration, excess noise, and increases in discharge pressure pulsation. To correct the problem, you may need to check for leaks in suction pipe joints, check for friction losses, pressurize suction vessels, raise the fluid level, or increase suction pipe size.
If there seems to be excessive vibration or the pump is noisier than usual, this might indicate loose mountings or loose couplings. It could also be due to worn bearings or a misaligned shaft. It’s important to inspect the pump to determine the root of the noise and vibration and correct the problem to prevent further damage.
Anyone who works with and around machines that use centrifugal pumps must know how to operate the pumps and troubleshoot common problems when there’s an operational failure. And while your employees may be knowledgeable about their job, formal training serves as an excellent reminder system and a refresher course for them.
Formal training gives employees and managers an opportunity to get up to date information on the different types of centrifugal pumps as well as improvements and changes since they were last trained formally.
Training equips workers with the knowledge and skills needed to help them to most effectively use and troubleshoot centrifugal pumps, and ensure that they are up and running properly. Employees learn to identify symptoms and causes of centrifugal pump failure.
They also learn how to inspect the system, safely disassemble the components, check internal parts, replace faulty parts, and reassemble the components. Seminars and courses also help ensure workers and managers observe industrial safety rules to keep machines, workers, and the facility safe and secure.
Are you considering having you and your workers trained in fixing and troubleshooting centrifugal pumps? Contact NTT Inc. today for more information about the centrifugal pumps seminars and courses that we offer throughout the year.
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