Xylem H-3551 - Manual (Page 8)

2-2 Installation
H-3551
2.2 Orifice and Sensor Connections
In its simplest form, a gas purge pressure measurement system consists of a gas source, a pressure
measurement device and an orifice tube all connected together in a “ T” arrangement. Because the H-3551
has the capability of purging the orifice line, a more complex connection is required. Do not use a simple
“T” connection to connect the bubbler and pressure sensor to the orifice line, instead, use the two
dedicated ports of the H-3551. The H-3551 includes an internal valve which isolates the pressure sensor
output from the orifice line during a purge sequence. This helps prevent a plugged orifice condition from
damaging the pressure sensor.
If you are using a pressure sensor other than the H-350XL you may need to take extra precautions to
further protect your pressure sensor. See Chapter3.
2.3 Recommended Field Installation Procedures
1. The H-355 must be wall mounted in the vertical position, with the manifold down. Mounting feet are
provided. A vertical mount helps ensure moisture will not accumulate in the internal pressure tank.
2. Connect the pressure line between the H-3551 and your pressure measurement device. This can be
done using the H-3551-Install kit. This kit is designed for use with the H-350XL. If your measurement
device has different connections, you will need to provide the appropriate fittings. You will need a 1/8"
NPT male tubing fitting for the sensor output. It is recommended that you use the 1/8" copper tubing
supplied in the install kit. The proper ferrules must be used to insure there are no leaks.
3. The H-3551 requires two separate power sources. First is the compressor 12V which powers the
compressor and control valves. This supply is typically made with heavy gauge wire to the gauge
station 12V battery. Second is the 12V which powers the control module. This source is supplied from
the pressure measurement sensor through the interface cable (provided), and into the control connector.
It is best to connect the compressor power first, then the control power second. If a pumping sequence
fails, the controller suspends pumping for a while to allow the battery to recharge. By connecting the
pump power first, the controller will not prematurely detect a dead battery and suspend pumping.
4. Generally, an external desiccator is required to dry the intake air. The desiccator prevents
accumulation of moisture in the tank, restriction and orifice line. Connect the output of the desiccator
to the port marked “intake”. Desiccators which employ “indicating” silica gel have the advantage of
visually showing the status of the desiccant. As the gel becomes saturated with moisture the gel turns
blue. See Appendix-B for further information and the specification for a recommended desiccator.