Campbell Scientific CVS4200 / BVS4300 Stationary Samplers - Manual (Page 34)

CVS4200 / BVS4300 Stationary Samplers
6.5.1 Using Velocity to Calculate Purge Time
Purge time of the sampler needs to be programmed based on the length of hose
and the velocity at which the liquid will travel through the hose. The formula
is l / v = p (length / velocity = min. purge time).
Adding a few seconds to the purge time is recommended to
ensure the line is fully cleared of any obstructions. NOTE
Example: 100 ft of hose, at 5 ft s –1 , requires a minimum 20 s purge time. 100 /
5 = 20 s. The number input for purge time should be a minimum of 20, but
preferably 24.
Standard purge time for 25 ft of intake tube is 10 s. Although a standard 25 ft
hose will sample in less than 4 seconds, 10 s is the minimum recommended for
proper clearing of the line.
6.5.2 Horizontal/Vertical Combinations
The velocity charts above measure only horizontal or only vertical. Most
applications will have combinations of both. With 61 m (200 ft) of intake
tubing, CVS/BVS Samplers are capable of drawing a sample above 0.6 m s
–1
(2 ft s –1 ) at 6.1 m (20 ft) of vertical. At 7 m (23 ft) of vertical with 61 m (200
ft) of intake tubing, sampling may or may not be successful, depending on
altitude and other factors. For more detailed information for your specific
application, please contact a Campbell Scientific applications engineer.
7. Operation
7.1 Use in Adverse Conditions
7.1.1 Exhaust
When the sampling sequence is in the suction cycle, the air removed from the
metering chamber and intake hose is vented externally through the exhaust
fitting. If the unit is installed indoors and detrimental air conditions exist in the
sample lines, the exhaust should be vented outdoors. To vent the exhaust,
connect a hose to the pump exhaust connection (13 on FIGURE 5-1) and route
the hose outdoors.
7.1.2 Instrument Air
Under adverse atmospheric conditions (humid, corrosive, etc.), compressed air
should be used to purge the cabinet and provide clean air for the pump intake.
Connect the tubing for the air tank to the fittings located on the left side of the
BVS enclosure (14 on FIGURE 5-1).
Failure to purge the cabinet in harsh conditions may
cause damage to the sampler and loss of warranty. WARNING
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