Technical Manual
Page 9
CODEL
OPS.109
Issue : B
Rev. : 1
Date : 23/10/13
Doc. i/d : 0109/6
Ref. : 090028
4.3.2. Air Purges
Before mounting the air purges ensure that air is supplied to the air purge unit. If this precaution
is not observed then the air purge and the optical surfaces may be severely contaminated.
The purpose of the air purges is to keep the windows of the transducers clean. Air may be supplied by one of
three methods:
Negative Pressure Duct. If the duct across which the instrument is measuring operates at a
negative pressure under
all
firing conditions, the isolating valve, pressure gauge and flow
restrictor may be removed and the negative draft in the duct allowed to draw-in ambient air
through the open purge inlet.
For positive pressure ducts, they must be supplied with either compressed air, or air from a blower.
Compressed Air. Using a fine flow regulator and filter, compressed air may be used to provide
the low flow required.
Blower Air. A blower may be used to provide air to the air purge. Customers may specify their
own blower; it should be able to deliver 5 litre/second (about 10cfm), against the working
pressure of the duct. CODEL can specify a blower if required.
The flange of the insertion tube is carried between the site mounting flange and the front flange of the air purge.
A rigid gasket is fitted between the site mounting flange and the insertion tube flange. Separate the front flange
from the air-purge by unscrewing the four retaining nuts. With the insertion tube and rigid gasket in place bolt
the front flange to the site-mounting flange using the four countersunk screws provided such that they pass
through the clearance holes in the insertion tube flange.
The rear flange is then offered-
up to the front flange onto the protruding studs taking care that the ‘O’-ring seal
on the flange locates smoothly into the central aperture. This is then re-secured by the four nuts that screw
down onto the adjustable flange. The arrangement should now appear as in Figure 3.
Figure 3 : Adjustable Mount Details
Insertion Tube
Site Mounting Flange
Stub Pipe (by others)
Rigid Gasket
Front Flange
Adjusting Nuts
Adjustable Flange
Retaining Nuts
Air Purge
Insulating Bush