It 's necessary to be concerned about vibration because it has a major affect on the performance of your pump. At least six components are seriously affected by vibration:

• The life of the mechanical seal is directly related to shaft movement. Vibration can cause carbon face chipping and seal face opening. Drive lugs will wear, and metal bellows seals will fatigue.
• Packing is sensitive to radial movement of the shaft. You'll not only experience excessive leakage, but excessive sleeve or shaft wear.
• Bearings are designed to handle both a radial and axial load. They were not designed for the vibration that can cause a brinneling (denting) of the bearing races.
• Critical dimensions and tolerances such as wear ring clearance and impeller setting will be affected by vibration. Bearing internal clearances are measured in tenths of thousands of an inch. (thousands of a millimeter)
• Pump components can be damaged by vibration.
• Bearing seals are very sensitive to shaft radial movement. Shaft damage will increase and the seals will fail prematurely.
• Pump and motor hold down bolts can become loose.

The vibration comes from a number of sources that include :

Mechanical causes of vibration

• Unbalanced rotating components. Damaged impellers and non concentric shaft sleeves are common.
• A bent or warped shaft.
• Pump and driver misalignment.
• Pipe strain. Either by design or as a result of thermal growth.
• The mass of the pump base is too small.
• Thermal growth of various components, especially shafts.
• Rubbing parts.
• Worn or loose bearings.
• Loose hold down bolts.
• Loose parts.
• Product attaching to a rotating component.
• Damaged parts.

Hydraulic causes of vibration

• Operating off of the pump's best efficiency point
• Vaporization of the product
• Impeller vane running too close to the pump cutwater.
• Internal recirculation.
• Air getting into the system through vortexing etc..
• Turbulence in the system
• Water hammer.

Other causes of vibration.

• Harmonic vibration from nearby equipment.
• Operating the pump at a critical speed. Watch out for this problem in variable speed and pulley driven pumps.
• Seal "slip stick" at the seal faces. This can occur if you are pumping a non-lubricating fluid, a gas or a dry solid.
• A pump discharge recirculation line aimed at the seal faces.

Unfortunately, most vibration data references bearing operation. There is little to no information available about mechanical seal vibration modes. The problem is further compounded by:

• The large variety of seal materials in use.
• Major differences, in design between popular brands of single and multiple seals.
• Availability of vibration damping in these seal designs.
• The wide spread use of environmental controls.
• The variety of fluids surrounding the seal

The vibration readings almost always means that the equipment has started to destroy its self. Most companies are trying to collect enough data to predict the remaining life before total destruction takes place.

The obvious solution to all of this is to adopt good maintenance practices that 'll eliminate most of the vibration and then try to install hardware that can live with the vibration you have left. Recording vibration makes sense only after good maintenance practices are in force.

Mechanical Problem Solutions

• Balance all of your rotating equipment. Balance is always a problem when you're pumping abrasives, or a slurry, because the rapid wear always destroys balance. In the higher speed pumps this wear can be very severe.
• Bent shafts are a problem. If you can straighten them go ahead and do it, but most attempts are unsuccessful. In the majority of cases you are better off replacing the shaft.
• Do a proper pump/ driver alignment using a laser.
• Always pipe from the pump suction to the pipe rack, never the other way
• Worn or loose bearings are caused by improper installation or allowing water to enter the bearing cavity. Labyrinth seals or positive face seals are the easiest solution to the water problem. Install bearings by using a proper induction heater to prevent contamination during the installation process.

• Water hammer is not very well understood by our industry, but we know how important it is to keep air out of the piping system.
• It's good practice to use one size larger suction pipe and then use a reducer to connect the piping to the pump. Do not use concentric reducers. Eccentric types are much better, as long as you do not install them upside down.

Solutions to other types of vibration

• The pump, or one of its components, can vibrate in harmony with another piece of equipment located in close proximity. Isolation, by vibration damping, is the easiest solution to this problem. This is a big problem with many metal bellows seal designs because they are lacking an elastomer that functions as a vibration damper.
• Critical speed operation is not a common problem unless you're operating with a variable speed drive. Changing the speed is the obvious solution. If that's not practical, changing the impeller diameter is another solution.
• Seal "slipstick" is a problem with non lubricants such as hot water or most solvents. If you're using o-ring seals, the o-ring is a natural vibration damper. Metal bellows seals require that a separate vibration damper be installed; usually in the form of a metal component vibrating and sliding on the shaft.
• Pump discharge recirculation lines can cause a vibration every time the impeller passes the recirculation line "tap off". This vibration will affect the mechanical seal and like all vibration, can be recognized by chipping on the outside diameter of the carbon face and worn drive lugs.