8
10.2 Low capacity
❑
Rotational speed too low for required capacity.
❑
Suction line or filter clogged or valve closed.
❑
The vacuum gauge reading is too high; Metallic cavitation sound.
❑
Air leaks into the suction line. The vacuum and pressure gauges oscillate. Check the suction line.
Attention: it is not easy to trace air leaks in the suction pipework. Listen for the characteristic hiss of air leaks near the joints.
❑
The by-pass relief valve is set at a pressure which is too low and causes some of the liquid to re-circulate within the pump Tighten the
regulation screws as indicated in the respective manuals; the pressure gauge will indicate a higher pressure.
❑
Air pockets may have formed within the suction line, especially if the pipework includes vertical bends
❑
The liquid vaporises before entering the pump, especially when trying to pump liquefied gases or liquids with high vapour pressure on
suction lift. The static suction lift is too high.
❑
The suction pipe is not sufficiently immersed into the liquid thus allowing liquid to enter the suction line. The vacuum gauge oscillates. The
pipe must be immersed into the liquid to a depth of at least twice the diameter.
❑
The liquid is too viscous for the rotational speed of the pump. The vacuum gauge reading is too high and a metallic noise comes from
inside the pump.
Fluidise the product by heating it; reduce the rotational speed of the pump; use tubing of a lager diameter.
❑
The pump cover has been mounted incorrectly.
10.3 Excessive pump noise
❑
Not enough liquid reaches the pump because the viscosity is too high. Reduce the rotational speed, increase the diameter of the suction
pipework, eliminate the friction losses in the suction line.
❑
The pump cavitates because the liquid is too volatile. Increase the diameter and/or reduce the length of the suction line. Raise the level of
the liquid in the suction tank; if necessary, mount the pump on flooded suction.
❑
Check the alignment of the couplings.
❑
The by-pass valve vibrates: tighten the regulation screw.
❑
Check the anchorage of the base plate and the pipework supports.
❑
Foreign bodies within the pump.
❑
The cover is mounted at 180
°
C with respect to the correct position.
10.4 The pump absorbs too much power
❑
Excessive rotational speed.
❑
Excessive viscosity: reduce the rotational velocity in accordance to the tables or else heat the product.
❑
Excessive pressure: increase the diameter of the delivery line, ensure that all of the valves are open and that the tubing is not clogged. Do
not exceed the pressures indicated in the table.
❑
Check the alignment of the pump (noise will generate).
❑
Tolerances are too tight for the liquid to be pumped.
The brushes overheat and seize, and the extremity of the idler pin on the cover heats to over 80
°
C. Stop the pump and increase the
tolerances as indicated by Varisco.
10.5 The pump wears out quickly
Rapid wear of the pump causes a sudden drop in performance. Following is a list of the main causes and respective remedies.
❑
The liquid is abrasive and contains solid particles. It is possible to note: grooves present on the surface, the brushes wear out quickly, the
tolerances are changes and the surfaces are irregular.
Clean the tubing thoroughly, install a suction filter. Reduce the delivery pressure. Use the AT and AW version..
❑
Corrosion and formation of rust or porosity of the surfaces, pitting on the surfaces or damage of the elastomers. Check that the materials
used are the more appropriate for that application, check that the liquid has not been contaminated and become corrosive.
Check that the concentrations indicated have not been altered and/or that the temperature of the fluid is within the limits allowed.
❑
Exceeding of the operative limits, excessive noise and breaking of the brushes, bent or broken shaft, vibrations etc. Use a lager pump,
consult the catalogue for an appropriate model.
❑
Tight tolerances, seizure of the pump, over-heating and breaking or damage to the bushes, excessive power absorption. Increase the
tolerances after having contacted Varisco.
❑
Noise reducer. Ensure that the lubrication of the reducer occurs according to the instructions.
❑
Misalignment, non-uniform wear (wear on just one side of the casing, of the packing or of the cover). Deformation of the casing due to
weight of the tubes, misaligned coupling, belts too tight, base plate not level.
Check the alignment of the pump while running in conditions as close as possible to operating conditions, support the tubing, check the
type of belt used.
❑
Dry running and pump seizure due to the deformation of the internal components, overheating and colour changes caused by excessive
heat. Ensure that liquid is present within the system, mount a foot valve when starting the pump or install an adequate alarm system or
motor cut-out for when the pump runs dry.
