| Possible cause and implicit solution |
| Suction filter, foot valve clogged. |
| Nominal diameter of suction line too small. |
| Foot valve does not reach down far enough into the delivery liquid. |
| Ground clearance of foot valve too narrow. |
| To many bends, elbows, valves, etc. in the suction line. |
| Shut-off valve in the feed line in unfavourable position. |
| Incorrect layout of suction line (formation of air pockets). |
| Valve(s) in the suction or feed line not fully open. |
| Screwed joints or flanges in the suction line not leak-tight. |
| Ingress of air via leaking valves and fittings in the suction line (stuffing box, etc.). |
| Static suction lift too great. |
| Static suction head too low (difference between pressure and suction flange at vapour pressure too low). |
| Delivery liquid contains too much gas and/or air. |
| Delivery liquid too viscous. |
| Insufficient venting. |
| Speed too low (number of revolutions of driver lower than nominal number of revolutions of pump). |
| Incorrect direction of rotation (electric motor connected incorrectly, leads on the terminal board interchanged). |
| Impeller clogged. |
| Impeller damaged. |
| Wear rings worn. |
| Separation of crystals from the delivery liquid (fallen short of the temperature limit/equilibrium temperature). |
| Pump unsuitable for parallel operation. |
| Type of the pump is unsuitable. |
| Incorrect designing of the pump for the given operating conditions. |
| Temperature of handled liquid too high. |