Tecfluid M21 Series - Manual (Page 5)

5
GAS MEASUREMENT. (Figure 3)
THE WORKING PRESSURE IS OF MAXIMUM IMPORTANCE for correct GAS measurement
readings as it directly affects the instruments scale.
Therefore if a meter is calibrated for 2 bar and it’s working at 1 bar there will be an error of 22%.
In order for the meter to work at the calibration pressure (nominal working pressure) and to obtain
a counter pressure that will maintain the floats equilibrium, the regulating valve should be mounted
as shown in Figure 3.
The flow should be controlled by the meter outlet valve while keeping the inlet one fully open. The
by-pass valve should be fully shut off.
If the regulation is done using the inlet valve, in open circuits or at low gas flow rates, inside the
meter the gas will expand which will sharply diminish its density, giving very serious reading errors.
Frequently, if the gas is regulated by the inlet valve, the float experiences an oscillating movement
which produces a shut off action until sufficient pressure is gained to overcome its weight. The
sudden pressure drop will make it fall when the gas escapes. This cycle is repeated until the valve
is closed or fully opened and then closed again, back to the desired flow rate.
This does not mean that this phenomenon will not occur again even if the flow is still regulated by
the inlet valve.
The valves must be closed during work stoppages or at the end of the work day to
avoid the float from hitting its stop on starting up, which could damage or bend the float
when driven with force by the fluid flow.
BY-PASS VALVE
3
2. REGULATOR AND SHUT
OFF VALVES
1. SHUT OFF VALVE
2. SHUT OFF
VALVE
BY-PASS VALVE
3
1. REGULATOR
AND SHUT OFF
VALVES
INSTALLATION FOR GASES INSTALLATION
FOR LIQUIDS
Figure 3 Figure 4
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