25 Ways to Break A Pump

2018-02-12T16:26:59+00:00 March 12th, 2015|

Over our 40+ years of processing harsh and acidic chemicals, we’ve seen our fair share of pumps that have been broken due to mismanagement and misinformation.

Take a look through our guide of 25 ways to break a pump and see if your business is making the same mistakes:

Relying on Reactive Maintenance rather than Predictive Measures

Too many times pump maintenance is overlooked or forgotten about within the maintenance procedures, leaning to only reactive maintenance if the pumps fails, leading to longer process down time, pump instability and expensive repairs. Instead, schedule biannually or quarterly pump maintenance including inlet cleaning, corrosion inspection, vibration monitoring and heat maintenance at the very least to ensure that cavitation or bearing wear is avoided.

Improper Bearing Fitting

Every time a bearing is replaced, or the shaft is cleaned, just a tiny fraction of the material on the surface is removed. Over time, a little adds up to a lot and can really affect the bearing clearance on the shaft. When this happens, expect the bearings to spin within the housing, or on the shaft.

Wrong Mechanical Seal or Seal Material Corroded

Lack of knowledge accounts for the majority of mechanical seal failures. Incorrect mechanical seal installation can lead to seal face damage, heat escalation and ultimately pump failure. Make sure you discuss thoroughly the type of chemicals you are processing with the pump manufacturer and type of mechanical seal you need.

Hard-Starting the Pump

The pump should be eased into pumping with a soft start. With a hard start, the pump tries to pump liquid as soon as it powers on. The pressure inside the pump causes the shaft to deflect towards the low pressure side causing the shaft to contact the casing. The misalignment will then cause seal failure. Remember to keep the suction valve wide open.

Not Detecting Vibration

Vibration can be a sign that the pump is seriously failing in its process. Vibration can damage wear rings, bushings, impellers and the bolts connecting the pump and motor. Vibration leads to the shortening of the life of the pump by over three quarters, so it is imperative that if excessive vibration occurs, your engineers take the necessary steps to find the root of the problem.

Mechanical Cause:

  • A bent shaft
  • Unbalanced rotating components
  • Pump misalignment
  • Pipe Strain
  • Loose Bolts

Hydraulic Cause: 

  • Operation not near the best efficiency point of the pump
  • Vaporization of the product
  • Air in the system
  • Turbulence in the system

Other: 

  • Vibration from other machinery

Not undertaking Initial Start Up Procedure

Improper starting up the pump can the motor to trip and the shaft to twist causing orbital movement directly related to internal parts contact, seal failure and shortening of the bearing life.

Pumping with a Bent Shaft

As mentioned previously, pumping with a bent shaft can cause vibration leading to the shortening of the pump’s lifespan. A bent shaft can a result of either operating off of the best efficiency point or pumping solids in a pump that cannot deal with solids effectively. When operating off of the BEP – too much pressure is applied to the shaft from one angle over the other causing strain. Pumping solids can get caught in the pump, leading to vibration, internal parts contact, bearing damage and ultimately premature pump failure.

Solids Trapped in Seal Housing

When the processed liquid and abrasives get stuck in the Seal housing and isn’t properly flushed out, expect to see a shortened seal life.

Pump Imbalance

Pump imbalance can create issues such as structural problems, reduced bearing life, increased vibration and reduced machine life. Vibration is the second biggest cause of pump failure and the largest cause of vibration is pump imbalance.

Incorrect Tools for Installation or Repair

Using a hammer to install couplings onto shafts or pipe wrenches for anything other than pipes. When it comes to pump, they are delicate machines that can crack if struck with a hammer.

Plugged Vanes

Plugged vanes or balance holes are caused by blockages from solids that have been pulled into the pump that are too large for the pump capacity. Plugged vanes lead to a decrease in performance, efficiency, priming issues, impeller imbalance and high vibration, resulting in seal damage.

Incorrect Wear Ringswear

A wear ring separates the high pressure zones of the pump from the low pressure zones. When clearances open up, the pump experiences increased slippage, and the high pressure liquid seeps back into the low pressure areas, causing a loss in efficiency. When clearance are too tight on the other hand, the wear right will cause galling and seizing of the pump.

Entrained Vapour in the Pump

Entrained vapour can be caused by a number of factors. Vortex in the tank, insufficient water source, steam injection or incorrect NPSH conditions. Entrained vapojur causes loss of performance, wear to the impeller and cutwater, and dry running of the seal due to vapour between the faces.

Pipe Strain

Pipe strain is unwanted pressure or movement in the piping system causing the pipes to pump on the pump. This can be caused by :

  • Improper design or installation of piping systems or machinery.
  • Thermal or pressure changes which could cause unwanted movement in piping systems.
  • The lack of, or improper design and placement of pipe supports.
  • Process changes, in which changes in the piping system were not factored in.

The likelihood is that the discharge piping is incorrectly or inaccurately installed creating stress on the pump casing that will detrimentally affect the reliable life of the seal and bearing.

Too Little Lubricationcorrosion

Too little lubricant can cause premature bearing failure, causing the bearings to seize and fail the pump. This is the same for too much lubricant which can entrap heat and retain heat inside the bearing causing oil leakages – shortening the life of the pump.

Incorrect Impeller Adjustment

Incorrectly adjusting the impeller can lead to increased slippage in the pump, creating more turbulence inside the pump, lowering efficiency and increasing pressure inside the stuffing box.

Poor Piping connected to the Pump

Much like the pipe strain (see #12), poor pipework connected to the pump can cause the pump to under-perform. Pipework designed with an immediate invert, bent or “U” can cause trapped air in the system. Designs with an immediate 90 degree bend before the pump can cause turbulence inside the pump. Both result in suction and cavitational problems for the pump.

Other side effects include:

  • Performance dropout
  • Impeller failure
  • Bearing and mechanical seal failures
  • Cracked casings
  • Leaks
  • Spills
  • Fires

Using the Wrong Impeller

Using the wrong sized impeller for the pump causes the pump to produce too much, or too little flow, running off of its best efficiency point. If the impeller is too big the pump motor has to work harder to pump the fluid, eventually causing it to burn out, shortening the life of the pump dramatically. If the impeller is too small it most likely will not generate enough flow or head. Again, its important to chat with the pump engineers or arrange a site visit to get down to the route of the problem, and correctly size the impeller to the operation.

Operating too far to the right of the Curve

Pumps are designed to run at the most efficient point by the pump manufacturer. This allows for safe pumping, at the most energy efficient point of the duty required. Running outside of the best efficiency point can not only reduce efficiency by cause a strained operation on the pump. This can quickly lead to excess re-circulation, lead, radial loss, vibration, high seal temperature and vastly lower efficiency.

Improper Alignment

Improper alignment is a serious cause of pump failure. Up to 50% of damage to rotating machinery is directly related to pump misalignment. This means increased vibration, premature seal and bearing failures and increased power consumption. Excessive misalignment can even cause breakage of mounts or pump casings.

It is important to check the alignment of the pump before it is fully operational. There are two types of misalignment:

– Angular Misalignment

Misalignment is a condition where the centerlines of coupled shafts do not coincide. If the misaligned shaft centerlines are parallel but not coincident, then the misalignment is said to be parallel (or offset) misalignment. If the misaligned shafts meet at a point but are not parallel, then the misalignment is called angular misalignment.

_aintroduction to machine vibration-144

– Parallel Misalignment 

If the misaligned shaft center lines are parallel but not coincident, then the misalignment is said to be parallel (or offset) misalignment. Parallel misalignment produces both a shear force and bending moment on the coupled end of each shaft.

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Crest Pumps Group deliver pumps that are mounted on a base plate and are pre-aligned at the factory to ensure that the pump stays properly aligned and protected.

Pumping Solids/Abrasive in the wrong Pump

Pumping solids or abrasives in a pump that is not set to deal with viscous media or solids can clog and break the pump. If the pump is improperly selected for the application at hand, expect to see a shortened life on nearly all components (casing, impeller, stuffing box, etc). We would advise that you consult the pump manufacturer – pumps can be designed to fit the expect specification of your application.

Wrong Chemicals for the PumpWrong Chemicals for the Pump

Pumps are designed for specific chemicals using the most efficiency, safe and reliable materials for the desired application. If the pump is then used for a chemical that the pump was not built for, the corrosive properties of the new application can erode the insides of the pump causing immediate pump failure and a potential spillage, disrupting your process, production line and the area around the pump if there is a leakage.

Consult our Chemical Compatibility Table for our up-to-date advice on what pump materials are suitable for different applications.

Operation at Shut off

When the discharge valve is partially or completely closed to manually control flow, it causes 100% of the input energy to be destructive. This leads very quickly to a build up of pressure and pump failure. Consult the pump manufacturer on how to control or get the optimal head, flow or pressure.

Mechanical Seal Installation Error

Improperly installing the mechanical seal will cause damage to the elastomers (O-rings) as well as a wide variety of other issues. Mechanical seals can be very sensitive as the faces are incredibly flat. Even a small about of dirt or oil (even from fingerprints) can cause the faces to mis-align.

[title_small title=”1: Running Dry”/]bent shaft

Both Mechanical Seal and Magnetic Drive Centrifugal pumps can suffer from running dry if the pump hasn’t been designed to combat it.

Allowing the pump to dry run can lead to catastrophic pump failure (depending on circumstance). For a mechanical seal pump, running dry could lead to pump cavitation and therefore seal damage. The mechanical seal could also experience thermal shock and under the right conditions could shatter within 30 seconds.

With a mag-drive pump, the bearings and shaft can rise in temperature due to the absence of liquid lubrication and subsequently melt the plastic casing.

 

Do you require more information about preventing an untimely cost to your process or help in finding the right pump for your application? Give us a call on 01425 627700.