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Twin Screw Pump Troubleshooting

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    Below are a troubleshooting and maintenance guide for Pomac Pumps’ PDSP Twin Screw Pump.

    Sanitary Twin Screw Pump Malfunctions

    What are the reasons from the malfunction of a Pomac Pumps’ PDSP Twin Screw Pump?

    A malfunction in a pump system may be caused by a number of reasons and is not necessarily the pump itself. Issues with the pipework or other fluid accessories within the system can be contributing factors. Another major contributing factor would be operating the pump in conditions that are extremely different to the ones provided at the time of specification.

    Consequently, it is always recommended to check the following first:

    • Has the pump been installed correctly?
    • Are the operating conditions still according to the initial specification?
    • Are the other fluid accessories within the pipework functioning correctly?

    In general, the following malfunctions can be identified:

    1. The pump provides no flow
    2. The pump provides irregular flow
    3. Capacity is too low
    4. Pump overheats
    5. Motor overheats
    6. Excessive Screw / Rotor wear
    7. Excessive wear of shaft sealing
    8. Pump vibrates excessively or makes too much noise
    9. Pump has seized
    10. Pump stops upon startup

    Below is a table of the possible causes and solutions of these malfunctions.

    MalfunctionCauseSolution
    12345678910
    XWrong Direction or RotationHave a qualified electrician revers the direction of rotation of the electric motor
    XThe pump is not completely filled with liquidFill the pump casing entirely with fluid and fit a non-return valve to the suction side
    XXXXInsufficient Suction Pressure / NPSHaIncrease the suction pressure, lower position of the pump further below the fluid level, enlarge suction pipe ø, shorten/simplify suction pipework, reduce operating speed, reduce product temperature
    XXXExcessive vapour is present in the suction line
    XXXAir is entering the suction lineCheck Connections
    XXXXGas in the suction lineVent suction pipe/pump casing
    XXXInsufficient static headIncrease the liquid level
    XXXXProduct viscosity is too highLower the operating speed/increase product temperature
    XProduct viscosity is too lowIncrease the operating speed / lower the product temperature
    XXXXXProduct temperature is too highCool the product/pump casing
    XXProduct temperature is too lowHeat the product/pump casing
    XXXXForeign particles are in the productClean the system / install a suction filter sized according to the passage of the max solid of the pump
    XXXXXXXThe pressure at delivery side is too highCheck piping for obstructions / simplify the discharge pipework
    XXXXXPump casing distorted by pipingCheck alignment/support the piping & install flexible couplings
    XXSpeed too highLower the speed
    XSpeed too lowIncrease the speed
    XXXXXXInsufficient flushingIncrease flushing capacity/pressure
    XXXXXXXWorn out bearings/gearsReplace the worn-out parts

    Inspection & Maintenance Schedule

    Routine inspection and maintenance can avoid unnecessary and expensive downtime as well as operating costs. It is recommended to regularly check:

    • If the pump functions properly – excessive noise levels may indicate wear problems to bearings and gears, dragging of screws on the pump casing or cavitation.
    • Pressure and Flow of the flushing system, if present
    • Temperature of the heating / cooling system, if present
    • Oil level in the gearbox – at standstill the oil level must be in the centre of the visual level indicator

    Oil Level Indication for a Twin Screw Pump

    Oil Changes

    • 300 operating hours after initial commissioning
    • Every 3000 operating hours or at least every 3 months
    • If not being used regularly, every 2000 operating hours, or at least every 3 months

     

    Inspection IntervalRefers to Inspection Duty

    Preventative Action

    DailyQuench or Flushing SystemCheck Quench or Flush Pressure / FlowAdjust when at standstill
    Gear BoxCheck Oil LevelsTop up if necessary
    Mechanical SealCheck for LeaksReplace when faulty
    Lip SealCheck for LeaksReplace when faulty
    SystemFunctional check of pumpSwitch off and find / resolve cause when irregularities are found
    SystemInspect ConnectionsRepair when leaking
    Take product sampleIf contaminated, check seal and flush seal chamber
    WeeklyDriveCheck if drive is operating within specSwitch off and find / resolve cause when irregularities are found

     

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