Testing validated the results of CFD analysis and the improvement obtained with a new wearing ring. There was an overall drop of 3 db, out of 96 db (dbA), in noise (Fig. 8) and a drop of peak-to-peak pulsation pressure ranges between 2 psi and 5 psi (Fig. 9) without affecting performance. Improved suction characteristics were obtained at low capacity.
CFD proved to be a useful tool in solving a difficult plant problem.
By John Pembroke, Senior Product Engineer, and Gene Sabini, Manager of Technology, Goulds Pumps, ITT Industries, Industrial Pump Div., Seneca Falls, NY; and David E. Littlefield, Senior Design Specialist, The Dow Chemical Co., Freeport, Texas.
Fraser, W.H., "Avoiding Recirculation in Centrifugal Pumps," Machine Design, 1982.
Fraser, W.H., Recirculation in Centrifugal Pumps, ASME, 1981.
Knapp, R.T., Daily J.W., and Hammitt F.G., Cavitation, McGraw-Hill, 1970.
McNulty, P.J. and Pearsall, I.S., "Cavitation Inception in Pumps," ASME Journal of Fluid Engineering, 1982.
Nelik, L. and Freeman, J., "Case 1: Cooling Water Pump Case Study-Cavitation Performance Improvement," Proceedings of the Thirteenth International Pump Users Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, TX, 1996.
Stepanoff, A.J., Pumps and Blowers, John Wiley & Sons, 1965.
Sulzer, Sulzer Centrifugal Pump Handbook, Elsevier Science Publishers, 1989.
Vleming, D.J., A Method for Estimating the Net Positive Suction Required by Centrifugal Pumps, ASME, 1981.
System factors affect noise
Pumping system design and installation are often significant factors in a chronic noise situation.
Pump design features that affect noise/pressure pulsation include:
Cutwater clearance is influenced by the impeller-to-casing distance and by the shape and number of impeller vanes passing the casing tongue.
Shape of the suction collector passage.
If the flow makes an abrupt change in direction as it enters the eye of an impeller, separation occurs.
Non-uniform supply to the impeller.
Double-suction pump casings impose an asymmetrical fluid velocity distribution entering the impeller eye because of the nature of their design.
Cavitation at the wear rings.
Position and contour of double-suction inlet stop piece (splitter).
Rotor imbalance, which can cause a low frequency rumble.
As the pump vibrates, bearing and seals can wear, which leads to noise problems.
Installation features affecting noise/pressure pulsation include factors in the follow these areas:
- Baseplate resonance;
- Poor foundation design; and
- Piping supports.
- Prerotation of the fluid entering the pump caused by poor intake or poor inlet piping design produces a low frequency rumble;
- Valves cavitating cause high frequency noise;
- Velocity of the fluid within the pipes can excite resonances and low frequency noise (pipe organ effects); and
- Horizontal elbow on double-suction pump suction causes non-uniform velocity/pressure distribution from side to side of double suction. In very extreme cases, cavitation damage has been observed on one side of the impeller and recirculation damage on the other. Similar problems occur when valves are incorrectly placed near the pump suction.
3. Driver/electrical noise.
- High-pitched noise caused by the electromagnetic fields excites alternating forces on the motor's rotor and stator;
- Variable frequency drives can also produce a high frequency noise caused by harmonics; and
- Noise emanating from fan-cooled motors.