Abstract
Cavitation in pumps must be detected and prevented. The present work is an attempt to use the simultaneous measurements of vibration and sound for variable speed pump to detect cavitation. It is an attempt to declare the relationship between the vibration and sound for the same discharge of 780 L/h and NPSHA of 0.754 at variable speeds of 1476 rpm, 1644 rpm, 1932 rpm, 2190 rpm, 2466 rpm, and 2682 rpm. Results showed that: the occurrence of cavitation depends on the rotational speed, and the sound signals in both no cavitation and cavitation conditions appear in random manner. While, surveying the vibration and sound spectrums at the second, third, and fourth blade passing frequencies reveals no indications or phenomenon associated with the cavitation at variable speeds. It is recommended to survey the vibration spectra at the rotational and blade passing frequencies simultaneously as a detection unique method of cavitation.
Highlights
Installation of pump is often sized to cope with a highest predicted discharge, which, may never occurred
The cavitation in variable speed pumps is detected by online comparing between the vibration acceleration at the rotational and blade passing frequencies, at which the levels at the rotational frequency are decreased while the levels at the blade passing frequency are increased or vice versa is detected, this is an indication for cavitating pump which is unique and not occurred for the case of no cavitation
For variable speed pump discharges 780 L/h with NPSHA of 0.754 m rotates at speeds of 1476 rpm, 1644 rpm, 1932 rpm, 2190 rpm, 2466 rpm, and 2682 rpm it is concluded that: 1) The occurrence of cavitation depends on the rotational speed
Summary
Installation of pump is often sized to cope with a highest predicted discharge, which, may never occurred. This over sizing is used in industry, and leads to wasted energy and damage to parts of the pump. Speed regulation is one of the best methods to control the pump discharge, it has many benefits include; energy savings, reliability enhancement, simple piping and connections, soft start and stop, and reduced maintenance. Lowering the pump rotational speed reduces the hydraulic forces on the impeller approximately with the square of the rotational speed. These hydraulic forces are generated as a result of the pressure profile inside the pump casing, and car-.
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