C
−
102-1-E
8
Flow
Probe
Flow control valve
Fig. 3.6 Piping Example to Prevent Negative Pressure (2)
3.6 Installation Location
Avoid locations such as:
(1) Near motors, transformers, or heavy electrical equipment
(2) Inaccessible for maintenance and inspection
(3) Temperature varies widely or vibration is excessive
(4) Potential risk of submergence
4. PROBE INSTALLATION
4.1 Screw-in Type (nominal sizes 3 to 15mm)
(1) Process connection is of screw-in type. By using dedicated unions, be sure to seal the end face of probe
(lining surface). Never apply a seal to threads as it is likely to cause unexpected trouble.
Fig. 3.5 Piping Example to Prevent Negative Pressure (1)
Probe
Lining
Seal face
(A)
(B)
Gasket
(Must be in place.)
Do not seal on threads.
Fig. 4.1
3.5 Prevention of Negative Pressure
In order to maintain a long-term service life of the
probe, take positive measures to eliminate
circumstances that can create negative pressure
in the pipeline.
(1) If both upstream and downstream valves
remain closed with fluid temperature higher
than that of the atmosphere, fluid contraction
may take place as the fluid cools down,
creating negative pressure in the enclosed
space of pipeline. You can solve this problem
by providing a negative pressure relief valve
near the probe.
(2) If a vertical piping continues downstream of
the probe:
While stopping or adjusting the fluid flow with
the upstream valve of flowmeter, negative
pressure can be created in the pipeline. To
prevent this condition, stop or adjust the fluid
flow with the downstream valve.
Flow
Upstream valve
Probe
Negative press. relief valve
Downstream valve
