Twin Screw Pump Troubleshooting

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 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