General Pumps and Sewage Pumps

Defects

Probable causes for the defect

Design for Maintainability (DfM) Guidelines
Excessive vibration

Insufficient vibration damping causing wear-out of parts

       Dented pump impeller

   Design

  • Ensure that pumps are properly sized to meet the required pressure. Head loss, frictional loss and loss at bends should also be considered.
  • Sewage pumps should be able to handle long and fibrous material. If required, pre-treatment (e.g. crushing) is provided.
  • Specify variable speed drives (VSD) that are able to handle both maximum and variable demand.
  • Ensure that the pump is mounted on an isolation bed (e.g. 150mm insulated padding) and that no site adjustment in height or position should be done.

Construction

  • Conform to the installation of pumps as per manufacturer’s instructions. Ensure proper construction of isolation beds and installation/mounting of equipment.
  • Special attention should be given for tightness of joints, and alignment of bearings and pipes.
  • Conduct testing and commissioning of the auto and manual interchange of duty and standby pumps.

Maintenance

  • Lubricate pump parts with oil or grease as per manufacturer’s instructions.
  • Conduct routine check, clean motor starter and all heavy current contacts, and replace worn parts.
  • Visually check for any damage or missing parts (screw, nuts, strainer, etc.).
  • Ensure that after installation, pump is tested with power on mode for any unusual vibration, noise, leakage or burnt smell.
Water not enough hot / takes long time to appear
  • Wrong design results in excessive ‘dead leg (the pipe length of cold water allowed to run off before hot water appears at tap spout)
  • The primary and / or secondary circuit is not insulated to prevent heat loss or insulation damaged with time.
  • Short circuiting in the piping of the primary and secondary circuit. Combustible insulation of the primary and secondary circuit of the hot water cylinder melts after some time.
 Design

Construction

Maintenance
Corrosion

 

Even a light covering of scale, as seen on these tubes, is enough to mask serious corrosion of the metal underneath - masked that is until it is too late.

Corrosion and pitting

 
  • Piping material not corrosion resistant or galvanic corrosion. Timely action (e.g. paint is helpful).
  • Protective coating lost /damaged during installation–improperly done.
  • Hard water reaches a temperature > 60ºC forms scales.
 Design

Construction

Maintenance

References
[1]  

Normative References/Standards Referred to for Air Handling Unit and Fan Coil Unit