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Operation
2Operation
Round bottles are used for sample containers. Pressure from a spring tensioned operating rod holds and seals the bottle
against a rubber gasket within the casting. The contact between the sample bottle and the gasket should be air tight and
should be tested by blocking off the air exhaust tube with a finger and blowing into the nozzle each time a bottle is fitted
to the sampler.
The axis of the sample container is inclined at an angle to the vertical which permits sampling to within 90mm of the
stream bed. With the instrument oriented into the direction of flow (nozzle horizontal and pointed upstream) a
continuous stream filament is discharged into the sample bottle during the period of submergence. The air displaced by
the sample is ejected through the air escape passage projecting from the instrument alongside the head and oriented to
discharge downstream.
A fixed static head differential between the intake and air exhaust facilitates sampling in low stream velocities and slack
waters.
Three nozzles, 1/8", 3/16" and 1/4" diameter, are supplied with each sampler.
One is chosen for each sampling cross section according to the velocity and depth to be sampled.
A clean bottle should be used for each separate sediment sample.
At least one suspended sediment sample is taken at each stream vertical selected in the cross section. In a sampling
operation, the intake nozzle is oriented upstream, directly into the current while the sediment sampler is lowered into the
stream.
Submerged obstructions directly upstream or adjacent to the sampler should be avoided to preclude interference with
the stream filament approaching the intake nozzle.
The sampler should be lowered at a uniform rate from the water surface to the bottom of the stream, instantly reversed,
and then raised again to the water surface at a uniform but not necessarily an equal rate. Each filled sample bottle when
removed from the instrument should be capped immediately and appropriately marked.
The sampler continues to take its sample in flowing water throughout the time of submergence, even after the bottle is
completely filled. If the bottle becomes entirely full, the sample may not be representative and should be discarded.
Although the capacity of the sample container is about 470ml, the tilt of the bottle is such that any sample containing
more than 440ml of a water sediment mixture may be in error.
In order to provide sufficient sample of a laboratory analysis, the length of time the instrument remains submerged
should be adequate to produce a sample volume greater than 375ml but not to exceed 440ml. It is generally preferable
to save an initial sample smaller than 375ml but larger than
300ml than to discard the sample on the spot and re-sample into the same bottle. Moreover, if the initial sample volume
is considerably less than
300ml, the stream vertical may be integrated a second time, or even a third time, each being additive to the same sample
bottle. A minimum sample of 350ml is suggested.
Sample Size
The volume of sample collected throughout any stream vertical is dependent primarily upon the mean stream velocity in
the vertical, the size of the intake nozzle, and the time of submergence of the instrument. The operator must regulate the
size of the sample accumulated by establishing the appropriate time period over which the sample is to be taken. Thus the
volume of the sample may be increased or decreased by varying correspondingly the sampling time. The attached graph
shows the relation between stream velocity and filling time to produce samples 395ml in volume for three different
nozzle sizes. The filling time in seconds represents the total time of submergence of the instrument and includes the time
involved in traversing the stream vertical in both the downward and upward direction.
2.1 Example
(Refer Diagram 1 )
Mean Velocity 1.2 metres/sec.
Nozzle 1/4"
Filling Time 10 seconds
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