Xylem H-3551 - Manual (Page 15)

H-3551
Operation 3-5
WARNING: THERE IS A DISTINCT POSSIBILITY OF DESTROYING YOUR
PRESSURE SENSOR. THIS CAN BE AVOIDED BY INSTALLING
AN ISOLATION VALVE BETWEEN THE H-3551 AND YOUR
SENSOR.
If a purge does not clear a plugged orifice line, the purge pressure will be applied to the sensor
output of the H-3551. The H-350XL has an internal valve which protects its precision pressure
transducer from a failed purge. When operating the H-3551 with a sensor other than the H-350XL,
the purge pressure could be applied to your sensor before the H-3551's internal pressure relief valve
can pop. It is your responsibility to verify that your sensor can handle the purge pressure, or install
an isolation valve between the H-3551 and your sensor. The valve must be closed prior to a purge
and remain closed until the purge is completed, or until the tank pressure falls below your sensor’s
maximum pressure rating.
3.4 Manual Purge
The H-3551 has an internal button which allows a manual purge to be initiated. This feature allows
you to clear a plugged orifice or verify the orifice is clear.
The Purge button is located inside the H-3551 enclosure, on the top corner of the control module.
Pressing this for one to two seconds initiates a purge sequence. The compressor will be turned on
and the tank pressure raised to the “Purge Pressure”. During this time, the bubble rate will rise
proportionally with the pressure. Next, the compressor is turned off and the purge valve is
actuated to dump the tank pressure directly to the orifice line. While the purge valve is actuated
the pressure sensor output is blocked by a valve to prevent the purge pressure from damaging the
pressure measurement system. During the purge, the orifice should produce vigorous bubbling with
the bubble rate falling eventually to zero. After a delay equal to the “Purge Delay”, the purge valve
is closed and the compressor is again turned on to restore the bubble rate to its normal value.
Note: When the button is pressed, if the tank pressure is already higher than the “Purge Pressure”
the purge sequence will not be initiated.