1. The pump delivers against an excessively high
discharge pressure
- open discharge valve further until the duty point
conditions have been attained (adjusted)
2. Excessively high back pressure
- fit an oversize impeller2)
- increase rotational speed
(applies to turbine or I.C. engine driven pumps)
3. The pump and/or piping are incompletely vented or
primed.
- vent or prime the pump and system completely.
4. Suction line or impeller clogged.
- Remove deposits in the pump and/or piping.
5. Formation of air pockets in piping.
- Alter piping layout
- If necessary fit a vent valve.
6. NPSH available is too low (on positive suction head
installation)
- Check liquid level in suction vessel.
- Open isolating valve in suction line fully.
- Install a different suction line if necessary, if the
friction losses in the suction line are excessive.
- Check the suction line strainer.
7. Excessively high suction lift
- Clean out suction strainer basket and suction piping.
- Check liquid level in the pit.
- Alter the suction line.
8. Entrainment of air through the stuffing box.
- Sealing liquid passages are clogged; clean them
out if necessary, arrange a sealing liquid supply
from an outside source, or increase sealing liquid
pressure.
- Fit a new shaft seal.
9. Reverse rotation.
- Change over two of the phase leads of the power
supply cable.
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