MAINTENANCE TROUBLESHOOTING

MAINTENANCE TROUBLESHOOTING M031

  • If a lot of carbon is remaining on the seal face it means that the seal is failing prematurely and not wearing out. Carbon/ graphite is the only sacrificial part of a mechanical seal. Use the guidelines in “Seal troubleshooting.”
  • Be familiar with seal installation problems
  • The rubber boot seal is different than most mechanical seals and offers unique troubleshooting problems.
  • You can see evidence of corrosion, damage and erosion on the pump wetted parts.
  • Look for metal parts that show discoloration because of high heat
  • You can see evidence of wear or damage to an impeller or other pump component.
  • Check that the pump is level. The bearing oil level is will be affected.
  • When he pump is being removed to be taken to the shop, look for:
    • Excessive pipe strain when the pump is separated from the piping.
    • Look for “Soft foot” when the pump hold down bolts are being removed
  • Check piping filters, strainers and pump cooling jackets to be sure they are cleaned
  • The wear rings should have been changed when their clearance doubled. Make sure they’re in place, sometimes we find one of them missing.
  • Check the inside of the lines to see if they coated with solids causing too much fluid friction. Calcium build up is typical of the problem.
  • Erosion problems have to be repaired.
  • See if an inducer was left off when the pump was assembled.
  • Make sure piping reducers are not installed upside down.
  • Check that there at least 10 diameters of pipe between the pump suction and the first elbow. If the elbow is too close you can have cavitation problems.
  • A gasket is protruding into the stuffing box of a split case pump. It is rubbing against the seal restricting its movement.

If you are on the floor, you can see the same problems that operators should be looking for:

  • Some of the pump components are getting too hot. You can smell or feel excessive heat
  • Make sure piping reducers are not installed upside down.
  • If a storage or head tank is being filled from the bottom rather than the top, the pump head is changing and could cause seal problems as the pump operates off its best efficiency point.
  • Listen for unusual noise.
  • You can hear and feel vibration
  • You can detect leakage coming from the stuffing box or seal gland. Make sure the leakage is coming from the pump and not a leaking flange above.
  • The pump is giving off a bad odor. The product may become too hot or the bearing oil is overheating.
  • The pump is running dry, causing it to loose suction. A tank level gage could be stuck, giving a wrong reading
  • The pump is operating off of its best efficiency point to satisfy the system needs. This causes shaft deflection
  • The pump is being started with the discharge shut, or severely throttled to save electricity during the start up procedure. This will move the pump off its best efficiency point and could damage the mechanical seal. Starting with the discharge valve wide open will also move you off the best efficiency point and may also trip the motor circuit breaker because of high amperage.
  • The pump was not vented properly at start up. It is losing its suction head. You cannot vent a running pump because centrifugal force will throw the fluid out leaving the air trapped inside.
  • The pump is surging
  • If the pump is in an awkward or hazardous location, you will want to use a C or D frame adapter to insure good alignment. Be careful using wash down hoses around pumps and motors
  • Don’t let welders use the pump as a ground for their welding rig. You can damage the bearings
  • Has someone painted the pump while it was in place? Sometimes they also paint an outside mechanical seal, restricting the movement of the springs and sliding components.
  • If you change the temperature, concentration, viscosity or, pressure of your product it can shorten the mechanical seal life
  • A motorized discharge valve is changing the system curve
  • A suction valve is being used to control flow. It can cause cavitation problems.
  • If you are pumping a slurry, be aware there is a critical carrying velocity to prevent solids from settling out.
  • The gage readings and tank levels are changing, but they are being ignored.
  • Cleaners are being flushed through the lines that are not compatible with a pump component. The rubber parts (elastomers) in mechanical seals are very sensitive to cleaning chemicals.
  • Pumps are running intermittently without the lines being flushed properly.
  • Frequent starts and stops can cause the fluid to crystallize, solidify, become viscous etc. affecting the mechanical seal performance. This is one of the reasons that most seal failures occur at startup after the pump has cooled down.

Good maintenance practices

  • Follow recommended piping installation procedures
  • Install vortex breakers in the supply tank to prevent air from entering the pump suction
  • Do not use filters or strainers in the pump discharge recirculation line to clean the recirculating fluid. They will clog and no one is going to clean them
  • Dynamically balance the rotating parts of the pump, preferably as an assembly.
  • Do your pump to driver alignment at operating temperature.
  • Eliminate pipe strain wherever possible.
  • Be sure the initial impeller adjustment is made at the pump operating temperature. Thermal growth can also change the mechanical seal face loading
  • Open impellers have to be adjusted when the pump capacity falls off and the amperage remains the same.
  • Be sure the vertical pump stuffing box is vented to a low point in the system.
  • Use suction recirculation for most seal applications.
  • Use hydraulically balanced seals for the lowest heat generation
  • Use cartridge seals so you can make impeller adjustments without changing the seal face loading.
  • Insure the bearing oil is being changed on a regular basis.
  • Insure that no water or solids are getting into the bearing case. Use labyrinth or positive face seals.
  • Stagger pipe hangers.
  • Do not use hardened shafts with mechanical seals; the seal set screws will slip.
  • Be careful of using oversized impellers to get more head. You may run too close to the cutwater causing cavitation problems.
  • If you are repairing the cutwater lip be sure it is the right length to prevent cavitation
  • Never substitute a globe valve for a gate valve. Globe valves offer much moirГ© resistance to fluid flow and will change the system curve
  • Be careful that loose parts are not left in the pump or piping after working on the equipment
  • If the pump is going  to be on intermittent service, seal environmental controls become very important, especially when the pump is stopped between batches. Constant running pumps are easier to seal because temperature, thermal expansion and thrust soonstabilizes.

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  • On February 16, 2018