PUMPS DO NOT WORK! AND OTHER CENTRIFUGAL PUMP FOUNDATIONS

PUMPS DO NOT WORK! AND OTHER CENTRIFUGAL PUMP FOUNDATIONS

Is the centrifugal pump giving you any problems? Here are a few guidelines given below that might help or at least help to minimise many of the usual problems associated with a centrifugal pump:

• If the centrifugal pump has not been primed, it may not work correctly. Therefore it is vital that the pump is re-primed and thoroughly checked. In addition, it must be ensured that the suction line is full of fluid.
• In case it is found that the suction line is jammed or clogged, the obstruction must be removed at the earliest. Likewise, if the impeller is jammed or clocked, the pump needs to be back flushed so that the impeller is cleaned.
• If the shaft rotates in the wrong direction, then the rotation has to be changed to the right direction. It can be determined by the arrow given on the casing.
• If the suction pipe or foot valve is not adequately submerged, there has to be adequate submersion. If required, a baffle may need to be used. If the suction lift is too high, the suction pipe will have to be shortened. If needed, the pump may need to be relocated close to the source.
• If it is found that the o-ring or the casing gasket has an air leak, the ring or the gasket needs to be replaced at the earliest. If there is an air leak in the stuffing box, readjustment or replacing the mechanical seal for the pack will solve the problem.
• If the impeller is partially clogged, it must be removed for cleaning or back flushed to remove the clog. If the clearance between the impeller and the casing is too much, the impeller clearance will have to be adjusted. If the suction head is insufficient, it has to be ensured that the suction line valve is completely open and there is no obstruction in the line. If the impeller is damaged or worn, it must be immediately inspected and replaced.
• If the pump initially starts but then stops pumping, it means the pump is improperly primed. The remedy is to reprime the pump. The suction line has vapour or air pockets. The piping has to be rearranged at intervals to remove these air pockets. In case of any air leak in the suction pipe, it must be repaired.
• If the bearings become hot, it means that the driver and the pump are improperly aligned. In such a case, the driver and the pump must be realigned. In addition, if the lubrication has not been done properly, the level of the lubrication and its suitability need to be checked.
• If the pump vibrates when running or is noisy, it indicates that the driver and the pump are improperly aligned. The remedy is to realign the driver and the pump. If the impeller is partially clogged, it must be back flushed, cleaned, or replaced.
• If the shutter impeller is bent or broken, they need to be replaced as per requirement. If the foundation is not rigid enough, the hold-down bolts of the motor and the pump need to be tightened, or the stilts need to be adjusted. If the bearings have worn out, they need to be replaced. If the discharge or suction piping is not adequately supported for anchors, then proper corrective measures must be taken. Finally, if the pump is cavitating, it has to be relocated to correct the problem.
• If there is excessive leakage from the stuffing box, it is so since the packaging gland has been improperly adjusted.  The gland nuts need to be tightened properly. If the stuffing box is improperly packed, it must be checked and replaced.
• If the mechanical seal parts are broken or worn, those need to be replaced. If the mechanical seal is overheating, the cooling lines and the lubrication has to be checked. If the sleeve or the shaft is scored, it must be replaced.

The Foundation Used For Centrifugal Pumps

The foundation of a centrifugal pump should be able to observe the torque and force extended by the pump without any shift in its position. In some cases, it must also resist the forces extended by the piping and associated drive connected to the pump.

The strength of the foundation, together with the vibration behaviour, is crucial to ensure that the pump functions reliably.

Foundation Of The Pump And Its Characteristics

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On a concrete foundation, a combined base plate along with the drive for the pump must be placed.

Table foundations composed of steel and concrete that rest on special anti-vibrating elements for vibration insulation against the environment are necessary. The individual components are fitted on the table using a base or individual frames.

A special pump foundation may not be required if the base plate is composed of concrete, steel or iron. However, the entire setup has to be rigid enough to prevent distortion so that small and medium-sized pump sets with medium load from the piping can be installed even without a foundation.

Pump Failures And How To Detect Them

If you are using a centrifugal pump, then it is important for you to understand why such pumps may frequently fail and what methods are available to deflect before things come to a standstill.

One of the biggest problems that reliability and maintenance teams face today is the growing skill gap. Few individuals available have the required expertise to diagnose and repair frequent and major faults that haunt these pumps. Pump failures do not just cause inconvenience but can lead to catastrophe as well. From a paper mill to a water treatment plant, a non-functional pump can directly impact production. Therefore these pumps must remain healthy and running at all times. For that, it is important to understand why these forms failed.

In more than 50 per cent of pump failures, five broad factors are taken into consideration:

Leakage Of The Mechanical Seal

In centrifugal water pump, most leakages happen at the interface between the two seal faces. However, there are instances when leakages may happen in the secondary sealing area. There can be numerous reasons for mechanical seal leakage. These include non-alignment of the seal ring, thermal distortion and dry running.

Processing Issues

Such failure happens when the pump is selected improperly for an industrial application, operating condition, or a specific purpose. Therefore it is essential to match the right pump depending on the nature of the specific application.

Bearing Problems

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According to various technical reports, the most common reason for bearing issues is improper lubrication, causing it to overheat. It happens in almost 80 per cent of the cases. The other causes include fatigue, overload, and improper bearing selection, among others.

Impeller Depreciation

Just like with the other failures, there can be several reasons for the wear and tear of the impeller. One of the most common reasons happens to be erosion. However, it can also result from an improper size pump leading to an imbalance in pressure.

Coupling Related Problems

The most common coupling failure happens due to the reasons such as improper lubrication, torsional vibration, unexpected environmental issues, overload and misalignment.

The easiest fix is to replace the faulty component. However, such a move sometimes does not cover the actual cause since there can be several reasons for damage. For example, if the pump is not properly grounded, it can leak current into the bearing and damage it. Another factor could be cavitation, which can damage impellers, bearings and seals over time. In both instances, simply replacing the damaged part resolves the issue. However, if the root cause, like grounding or cavitation, is left unattended, the issue will be repeated. So what is the way to detect the root cross problem before it manifests physically, thereby hampering operation and leading to revenue loss. One of the ways is to go for condition monitoring technology.

How Can Condition Monitoring Technology Help To Track Down Pump Failure?

Condition monitoring technology is capable of keeping track of the pump operation using a signal.  The signals could be noise, temperature, vibration and so on. The main thing here is the ‘footprints of failure’. Whenever a fault develops, it changes the normal pattern uniquely. The condition monitoring system is capable of tracking and identifying these changes. In fact, the system can even detect a few issues much sooner than any other approach.

To come up with the best condition monitoring strategy for the pumping system, various factors need to be considered, including the fault type that needs to be monitored, the pump environment and the process of its operation. A condition monitoring system usually consists of essential technologies like vibration analysis, oil analysis, electrical signature analysis, infra-red thermography and acrostic emission analysis.

By keeping track of the current, oil, voltage, vibration, sound and heat, it is possible to have an early insight into the failures of a centrifugal pump. It can also help to understand what technique or approach would work best and in what condition to keep a critical centrifugal pump up and running all the time.