Cavitation in a PTF will take place when the local pressures fall close
to or below the vapor pressure of the liquid product. The formation of bubbles and their
collapse or local vaporization of product as it passes over the rotor blade surface can
cause erratic behavior in the PRECISION TURBINE FLOWMETER. Maintaining a system
backpressure of 2 times the PTF pressure drop plus 1.25 times the product vapor pressure
is sufficient to prevent cavitation as shown by the following formula:
BP= (P x 2) + (VP x 1.25)
Where,
BP= Required back pressure
P= Pressure drop at maximum flow
VP= Absolute vapor pressure at maximum temperature
Cavitation usually causes the rotor to speed up at the high flow rate
due to the increased flow volume and causes the accuracy curve of the PRECISION TURBINE
FLOWMETER to be adversely affected. Sustained over-speeding of the rotor can lead to
damage to the meter.
