OPERATION OF VRAE2 - 232.8 Integrated Sampling PumpThe VRAE multi gas monitor includes an integratedsampling pump. This is a diaphragm pump providing 400 ccper minute flow rate at the high setting. Connecting a 1/4inch Tygon tubing with 1/8 inch inside diameter to the gasinlet port of the VRAE, this pump can pull in air samplesfrom 200 feet away horizontally, or 90 feet vertically (seeTechnical Note 140 for tubing volumes and delay times).A low pump speed is the factory default setting, which willreduce the flow rate by about 25%, and increase battery lifeby about 5%, and result in an increased LEL sensor lifetime.The low speed is the default setting, so to achieve the highspeed performance, this needs to be switched to high (seeSection 4.7 for details of how to select the pump speed).A high pump speed is required when measuring certain gasesin order to reduce the absorption of these gases by thematerials in the gas passage. These gases include: Cl2, ClO2,PH3, NH3, and HCN.If liquid or other objects are sucked into the water trap in theinlet port and cause the pump to stall, the electronics of themonitor will detect the obstruction and shut down the pumpimmediately. The alarm will be activated and a flashing errormessage “Pump” will be displayed in the LCD display. Theuser needs to acknowledge the pump shut off condition bypressing the [Y/+] key to re-start the pump.
