OPERATION OF VRAE
2 - 23
2.8 Integrated Sampling Pump
The VRAE multi gas monitor includes an integrated
sampling pump. This is a diaphragm pump providing 400 cc
per minute flow rate at the high setting. Connecting a 1/4
inch Tygon tubing with 1/8 inch inside diameter to the gas
inlet port of the VRAE, this pump can pull in air samples
from 200 feet away horizontally, or 90 feet vertically (see
Technical Note 140 for tubing volumes and delay times).
A low pump speed is the factory default setting, which will
reduce the flow rate by about 25%, and increase battery life
by about 5%, and result in an increased LEL sensor lifetime.
The low speed is the default setting, so to achieve the high
speed performance, this needs to be switched to high (see
Section 4.7 for details of how to select the pump speed).
A high pump speed is required when measuring certain gases
in order to reduce the absorption of these gases by the
materials in the gas passage. These gases include: Cl
2
, ClO
2
,
PH
3
, NH
3
, and HCN.
If liquid or other objects are sucked into the water trap in the
inlet port and cause the pump to stall, the electronics of the
monitor will detect the obstruction and shut down the pump
immediately. The alarm will be activated and a flashing error
message “Pump” will be displayed in the LCD display. The
user needs to acknowledge the pump shut off condition by
pressing the
[Y/+]
key to re-start the pump.
