GE DewPro MMY30, User Manual

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November 2005
2-2 Installation Guidelines
Method I - Orifice at
Outlet
Figure 2-1 below illustrates installation at the orifice at the outlet.
Figure 2-1: DewPro Installation at Orifice at Outlet
Pressure Dewpoint
Air dryers producing general instrument air are typically specified
with a pressure dewpoint rating. The majority of dryers operate in a
dewpoint range between -40°C and -75°C (-40°F and -100°F). A
pressure of 7 to 8 bar (= 100 psig) is very common.
Air Flow
The DewPro is designed to measure the pressure dewpoint. By
restricting the flow at the outlet of the integral bypass with an orifice,
the sensor monitors the dewpoint at process pressure. The bleed-off
air to the atmosphere at 7 to 8 bar (100 psig), is approximately 70 cc/
min. (28 L/h or =1.0 SCFH cfh). For smaller sized dryers of 3m
3
/
min.(=100 cfm) the air loss is only 0.002% of the air production and
is negligible. Despite the very low flow rate through the bypass as
shown, the air sample in the DewPro bypass chamber is refreshed
every second due to the small volume design. As a result, the sensor
sees changes in moisture instantaneously. Due to the low flow rate,
the flow velocity is also very low at <0.01 m/sec. (=34 m/h).The low
flow velocity prevents the inlet filter from clogging since there is not
enough kinetic energy to push dust particles into the filter.