Yokogawa digitalYEWFLO (DY) User Manual download pdf (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

/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 × 17.3 + 1.3 × 47.4

= 108.3 kPa abs

Since the operating pressure of 120 kPa abs is

higher than 108.3 kPa abs, no cavitation occurs.

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Yokogawa digitalYEWFLO (DY) User Manual Page 129