Very often, here at Sintech pumps, we are asked this question by our customers, “How long will my pump operate?” Our answer remains the same, “It depends.”
The lifetime of a pump depends on several factors including maintenance, operating conditions and more. Generally, pumps can operate for 15 to 20 years without any troubles and in several cases, it can even last longer, even up to 25 years or more, if it’s operated and maintained at the best operating points.
Coming to the challenging question, what are the factors that end users can control to extend a pump’s life? Here, we present you with the top notable factors that impact the life of your pump.
- Radial Force
According to pump experts, one of the biggest reasons why centrifugal pumps fail is the wear and tear of mechanical seals and bearings. Consider the seals and bearings of your pump as the “Canaries in the coal mine.” These components act as early indicators of a pump’s health and help you get an idea of what’s happening inside the system.
As any pump operator will let you know, the best practice is to operate a pump as close as possible to the BEP (Best Efficiency Point). When you operate your pump at the BEP, it experiences the lowest radial force possible. When you operate your pump away from the BEP, the radial forces generated will try to bend and deflect the shaft, which in turn leads to reduced bearing life.
- Oil Contamination
More than 85% of all ball bearing failures are a result of oil contamination due to either dirt or other foreign substances or even water. Adding just 250 ppm (parts per million) of water it reduces bearing life by 4x times.
One of the critical factors in pump operation is oil service life. You can consider operating a pump similar to that of the operation of a car. Just like you have to change the oil after clocking particular kilometers in your car, you have to replace the oil in your pump regularly.
- Suction Pressure
Other factors that play an integral role in determining bearing life are driver alignment, suction pressure and pipe strain. Let’s take the case of a single-stage overhung process pump. Here, the resultant axial force on the rotor is pulled towards the suction, which in turn generates a counteracting suction pressure that further reduces the axial force.
This reduction in axial force decreases the thrust bearing loads, which extends the
Pump life.
- Driver Alignment
If the pump and driver overloads are misaligned it causes an overload on the radial bearing. The radial bearing life increases exponentially when calculated with the driver misalignment. For instance, even with small misalignment of just 0.06 inches, the bearing or coupling issues reduce months of operation.
- Pipe Strain
This happens when the suction or discharge pipe and the pump flanges are misaligned. Even if the pump has a robust design, the pipe strain can quickly transmit the high forces to the bearings, thereby reducing the life of the pump.
The strain caused by the pipe make the bearing to be out of or incongruent to the other bearings, thereby causing the centerlines to be positioned in different planes.
- Properties of the Pumped Fluid
The key properties of the pumped fluid like specific gravity, viscosity, and pH all play a role in determining the life of the pump. If the pumped fluid is caustic or acidic in nature, the parts of the pump that come in contact with the fluid like the impeller and casing are likely to be corroded soon. Similarly, the density of the fluid (the number of solids suspended in it), the size and shape of the dissolved solids and abrasive qualities all determine the life of the pump.
- Mode of Operation
The severity of the pump’s service is also another major factor that determines the
Pump life. The question to be addressed here is, “how often the pump will be stopped and started during a particular time?”
For instance, pumps that are stopped and started every few seconds are likely to be worn out faster than pumps that operate continuously. If your mode of operation is such that the pump is shut down and started in quick succession, then you need to consider an alternative design that suits this particular application.
In such cases, submerged pumps work better than suction lift pumps, this is because the lift in the latter category requires more work.
- Net Positive Suction Head A/R Margin
The higher the margin of NPSH
A (Net Positive Suction Head) over NPSH
R, the lower are the chances for pump cavitation. Cavitation causes damage to the pump’s impeller, which in turn causes vibrations that affect the bearings and seals.
- Speed of the Pump
The speed of the pump’s operation is another vital factor in determining the life of the pump. For instance, a 750-rpm pump will wear out faster than a 350-rpm pump.
- Impeller Balance
When the impeller is unbalanced in a vertical or overhung pump it causes a condition called as Shaft whip. This deflects the shaft just like a radial force. Sometimes, both shaft whip and radial force shaft deflection can occur at the same time.
For ideal operation, the impeller must be balanced according to the standards defined by the ISO (International Organization for Standardization). If the impeller gets trimmed for any reason, it must be rebalanced.
- Pipe Geometry
This denotes the mode of loading the fluid into the pump. For instance, using a vertical elbow in the pump’s suction side causes lower deleterious effects than a horizontal elbow. This is because the impeller is loaded evenly causing the bearings to be loaded evenly.
- Pump Operating Temperature
Whether you use a cryogenic or hot pump, the operating temperature, especially the rate at which the temperature changes have a large effect on the reliability and the life of the pump.
- Casing Penetrations
One of the reasons why casing penetrations are optional and not the standard recommended practice is because it influences pump life. Very often, customers have the casing drilled for vents, drains, instrumentation or gauge ports. Every time, you drill into the casing, it acts as a stress riser thereby opening the casing for stress cracks and corrosion.
Final Thoughts – Pump Life depends on a whole lot of Variables
While this list is in no way exhaustive, these are the top factors that influence the life of your pump. If you have any further queries on finding the optimal operating conditions for your pump,
get in touch with our pump care experts, here at Sintech, India’s leading manufacturer and supplier of industrial and commercial pumps.
