Yokogawa digitalYEWFLO (DY) - Manual (Page 129)

<13. GENERAL SPECIFICATIONS>
13-19
IM 01F06A00-01EN
 Cavitation
(Minimum Back Pressure, Liquid service
only):
Cavitation occurs when the fl ow line pressure
is low and fl ow velocity is high during fl uid
measurement, preventing correct measurement
of fl ow rate. The optimum line pressure can be
obtained from the following equation.
P = 2.7 ×
P + 1.3 × Po ········· (7)
Where,
P: Line pressure, 2 to 7 times as large as
internal diameter on downstream of
fl owmeter body surface. (kPa absolute).
∆P: Pressure loss (kPa). Refer to the item
above.
Po: Saturation liquid vapor pressure at operating
temperature (kPa absolute).
(Example) Confi rmation of presence of
cavitation Suppose that the line pressure is 120
kPa abs and the fl ow rate scale is 0 to 30 m
3 /h.
It is only necessary to confi rm the pressure at
the maximum fl ow rate ; therefore, the saturated
steam pressure of water at 80°C is as follows
from the table of saturated steam pressures:
Po = 47.4 kPa abs
Therefore, substitute this value in equation (7):
P = 2.7 Ч 17.3 + 1.3 Ч 47.4
= 108.3 kPa abs
Since the operating pressure of 120 kPa abs is
higher than 108.3 kPa abs, no cavitation occurs.