Oval EX DELTA, EX DELTA-DIA, Руководство пользователя

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14
D-546-9-E
5.4 Ripples
Compressors, Roots blowers and other ripple pressure generating sources could adversely affect meter
performance. Minimize pulsating pressures by referring to the following formula:
N ＜ 22ρV
2
(Pa)
where N: Pulsation pressure (Pa)
ρ: Density (kg/m
3
)
V : Minimum velocity (m/s)
If pulsation pressure is excessive, the following measures should be taken into consideration:
① Locate the source of pulsations downstream of the meter or locate it as far from the meter as possible.
② Provide a pulsation attenuator, such as a chamber or pulsation snapper.
③ Shut off valves upstream and downstream of the meter when fluid flow is interrupted (as a precaution
against erratic signal generation at zero flow).
5.5 Prevention of Cavitation (liquid service)
To prevent Cavitation, line pressure should be maintained above the level calculated by the following formula:
P ≧ 2.60 ΔP + 1.25P
0
(MPa [abs])
where ΔP: Pressure loss (MPa [abs])
≒ 1.2ρV
2
×10
－6
P
0
: Steam pressure of liquid (MPa [abs])
ρ : Density (kg/m
3
)
V : Flow velocity (m/s)
5.6 Prevention of Excessive Flowrate
To ensure long meter life, transient flowrates should
be held below 1.6 times the meter’s maximum
rating. Shown below are typical examples in steam
measurement where excessive flow is often
encountered:
Examples where meter’s maximum rating is
exceeded on a momentarily basis
In steam measurement, when P1＞ P2, quickly
opening the valve will result in a fluid flow at a rate
dependent on the line resistance (mainly valve port
position in “A” or meter resistance in “B”). The
resultant rate of incoming flow is the sum of
downstream pipeline volume and consumption, but
if pressure differential across the valve is great, the
fluid velocity will easily reach the sonic speed,
momentarily well in excess of meter’s maximum
rating. (Such phenomenon is often experienced at
system startup or in batch operation.)