Back-Purging System
Method 2 Section
6.1.2
“...T
he static and impact pressure holes of standard pitot tubes are
susceptible to plugging in particulate-laden gas streams. Therefore, whenever a standard pitot tube
is used to perform a traverse, adequate proof must be furnished that the openings of the pitot tube
have not plugged up during the traverse period.
This can be accomplished by comparing the velocity head (Δp) measurement recorded at a selected
traverse point (readable Δp value) with a second Δp measurement recorded after "back purging" with
pressurized air to clean the impact and static holes of the standard pitot tube. If the before and after
Δp measurements are within 5 percent, then the traverse data are acceptable.
Otherwise, the data should be rejected and the traverse measurements redone. Note that the
selected traverse point should be one that demonstrates a readable Δp value. If "back purging" at
regular intervals is part of a routine procedure, then comparative Δp measurements shall be
conducted as above for the last two traverse points that exhibit suitable Δp measurements.
”
If water or debris blockage is suspected, using an aspirator pump (squeeze bulb), apply a small
amount of pressure at the affected Audit Port (A1, A2, A2, A4, A5)
Figure 10
NOTE: Take care in pressurizing the Audit Ports so the Transducer(s) will not be damaged.
If there still appears to be a blockage, disconnect the sample lines affected from the UINC-3D-## and
apply pressure to the affected sample line (P1, P2, P3, P4, P5) using an aspirator pump or some
other pressure generating device.
Figure 11
Figure 10 Using A-350 pump to pressurize P1 Line
through A1 Port on the XC-3D55 Console
Figure 11 Using A-350 pump to pressurize P1 Line
coming directly out of Probe Extension
Revision:01 Page 17 of 23 9/26/2017