Pump Cavitation
PROBLEM:
SOLUTION:
BENEFITS:
To operate properly Centrifugal Pumps require 10 pipe diameters or more of straight pipe at their inlet, to dissipate the elbow induced non-uniform flow. When pipe diameters become large, this requirement becomes hard to meet. As a result, non uniform flow enters a pump resulting in a flow imbalance in the impeller. In the case of a double-suction pump, induced axial unbalanced vibration, head loss, and impeller cavitation occur.
Figure 1a and 1b - Top view of double-suction pump showing how a plain elbow (a) creates cavitation while a CRV® (b) promotes an even fluid distribution.
In Figure 1b, a balanced, uniform flow is seen as a result of using a CRV® . The CRV® is a proven flow conditioner which has solved thousands of industrial pumping installation problems.
A Case History
Figure 1 - CRV® installation just upstream of a short radius elbow and overhung centrifugical pump.
Figure 1 shows the feed piping configuration of a 3,500 rpm pump utilizing an eight inch CRV®. Prior to installing the CRV® , the pumps operation had been noisy and the unit required an overhaul every 4 months. The vibration spectra of the pump before and after the installation of a CRV® are shown in Figures 2a and 2b. The dramatic reduction in measured cavitation (6-14 range on the frequency scale) also resulted in a reduction in impeller imbalance (1 on the frequency scale). This reduced the noise; extended seal, bearing, and impeller life; and increased delivered head and flow. Prior to the CRV® s installation, three identical pumps in parallel operation were required to deliver the required flow rate. After CRV® s were installed before the elbow of each pump, two pumps met the flow rate requirements, and the third pump served as an installed spare.
Figure 2a & 2b
- Comparaison vibration spectra of 3,500 rpm double-suction pump without CRV® (a) and with CRV® (b).