Oval EX DELTA II, Инструкция по эксплуатации

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D-583-2N-E
2
Fig. 5.3
[B]
[A]
5.5 Prevention of Cavitation (liquid service)
To prevent cavitation, line pressure should be maintained above the level calculated by the following formula:
P ≧ 2.60ΔP + 1.25 P
0
(MPa [abs])
where
ΔP : Pressure loss (MPa)
≒ .2
ρ
V 2 ×0 −6 (MPa)
P
0
: Stream 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 .6 times the meter's maximum
rating. Shown below are typical examples in
steam measurement where excessive flow is often
encountered:
In cases where the flowrate exceeds the
maximum of meter rating momentarily.
In steam measurement, when P >P
2
, quickly opening
the valve will result in a fluid flow at a rate depending
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.)
5.7 Prevention of Slug Flow
This meter can measure both gases and liquids, but slug flows (where gases exist in the process liquid) will
produce a loss of metering accuracy.
5.8 Keep the Pipe Filled with Process Fluid
When making a liquid measurement, ensure that the piping remains full of the process liquid. Installation in
locations where it is difficult to keep the piping filled with the process liquid, or where bubbles tend to collect
should be avoided.
5.9 Bypass Line
Fig. 5.4
For maintenance and servicing purposes, it is a good
practice to provide a bypass line. Valves upstream
and downstream of the meter should be of a design
which will not disturb fluid flow pattern, such as ball
valves (full bore type), in this arrangement (see Fig.
5.4).
For general considerations to be observed, refer to
JIS Z 8766, "Flowrate Measurement Methods with
Vortex Shedding Flowmeters".
DOWNSTREAM
VALVE
METER
UPSTREAM
VALVE
VALVE IN BYPASS LINE
FLOW
P1
P2
FLOW
P1 P2
FLOW
VALVE
METER
VALVE METER
GAUGE
GAUGE