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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.

    Malfunction Cause Solution
    1 2 3 4 5 6 7 8 9 10
    X Wrong Direction or Rotation Have a qualified electrician revers the direction of rotation of the electric motor
    X The pump is not completely filled with liquid Fill the pump casing entirely with fluid and fit a non-return valve to the suction side
    X X X X Insufficient Suction Pressure / NPSHa Increase 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
    X X X Excessive vapour is present in the suction line
    X X X Air is entering the suction line Check Connections
    X X X X Gas in the suction line Vent suction pipe/pump casing
    X X X Insufficient static head Increase the liquid level
    X X X X Product viscosity is too high Lower the operating speed/increase product temperature
    X Product viscosity is too low Increase the operating speed / lower the product temperature
    X X X X X Product temperature is too high Cool the product/pump casing
    X X Product temperature is too low Heat the product/pump casing
    X X X X Foreign particles are in the product Clean the system / install a suction filter sized according to the passage of the max solid of the pump
    X X X X X X X The pressure at delivery side is too high Check piping for obstructions / simplify the discharge pipework
    X X X X X Pump casing distorted by piping Check alignment/support the piping & install flexible couplings
    X X Speed too high Lower the speed
    X Speed too low Increase the speed
    X X X X X X Insufficient flushing Increase flushing capacity/pressure
    X X X X X X X Worn out bearings/gears Replace 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 Interval Refers to Inspection Duty

    Preventative Action

    Daily Quench or Flushing System Check Quench or Flush Pressure / Flow Adjust when at standstill
    Gear Box Check Oil Levels Top up if necessary
    Mechanical Seal Check for Leaks Replace when faulty
    Lip Seal Check for Leaks Replace when faulty
    System Functional check of pump Switch off and find / resolve cause when irregularities are found
    System Inspect Connections Repair when leaking
    Take product sample If contaminated, check seal and flush seal chamber
    Weekly Drive Check if drive is operating within spec Switch off and find / resolve cause when irregularities are found


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