Sampling apparatus has a syphon with a longer arm (19) leading to a needle sampling station (20) from which extends a shorter arm (21) of the syphon. Liquid flow structure including a reverse flow diverter (10) is used to produce forward and reverse flow in the syphon and, on reverse flow, reduced pressure at the needle is produced by the head N of liquid, and during reverse flow some liquid enters a sampling bottle (24) through the needle (22). The needle extends into a T-piece and has a lower end at or below the mid line of the lateral leg of the T.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to sampling. 
This invention concerns a sampling apparatus comprising a source of liquid 
to be sampled, a sample station elevated with respect to the source, a 
first pipe for delivery of liquid from the source to the sampling station, 
a second pipe extending from the sampling station, the first and second 
pipes respectively forming longer and shorter arms of a syphon, a needle 
at the sample station having one end in a flow connection between the 
first and second pipes, a bottle at the sample station for receiving 
sample liquid through the needle, and means for causing delivery and 
return flows of liquid in the first pipe from the source to the sample 
station so that on the delivery flow liquid flows past the one end of the 
needle to the second pipe to reduce the pressure in the bottle and on the 
return flow a syphon effect is created and liquid flows from the second 
pipe past the one end of the needle to the first pipe and sample liquid 
flows through the needle into the bottle. The means for causing delivery 
may comprise a reverse flow diverter and means for operating the reverse 
flow diverter. 
There may be a T-piece connection at the sampling station, the leg of the T 
being connected to receive liquid delivered to the station, one branch of 
the T being connected to the second pipe, and the other branch being 
closed by a plug through which the needle extends, said one end of the 
needle in the T-piece being at or below the level of the centre line of 
the leg. 
The length of needle in the T-piece may have a greater internal diameter 
than the needle in the bottle.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
Referring to the drawings, pulsed flow from a Reverse Flow Diverter (RFD) 
is used to supply active liquor to a sample station and, in the liquor 
back-syphon stage of the cycle of operation, initially evacuate a sample 
bottle and ultimately draw liquor into the bottle. The advantages of this 
system are that liquor hold-up at the sample point is negligible, the 
system could be part of an RFD-fed liquor transport line, and only very 
short lengths of capillary making up the needle are necessary. In some 
cases the needle, when not fitted with a sample bottle, is not above 
atmospheric pressure when liquor is present. A reverse flow diverter 
comprises two opposed passages which diverge as they extend away from a 
chamber, and at least one transverse passage leading to the chamber. 
The arrangement of an RFD-fed sample point is shown in FIG. 1. The 
operating cycle of the RFD 10 is such that on the drive stroke, the charge 
vessel 11 is pressurized with compressed air through line 12 from supply 
13 including a timer until the liquor level in the charge vessel 11 is 
driven down to a position just above the outlet 14. Liquor is forced 
through the RFD; the input side of the RFD increases the velocity and 
reduces the pressure of the liquid and the output side recovers the 
pressure. During the drive part of the cycle, the pipework 19 from the RFD 
10 up to the sample point 20, and the pipework 21 from the sample point 
back to the feed tank, are filled with liquor and the arrangement of a 
sample needle 22 with respect to a sample `Tee` piece 23 is such that a 
sample bottle 24 is partially evacuated, because of flow from pipe 19 to 
pipe 21 causing reduced pressure in the needle, and is never pressurized. 
After a predetermined but adjustable time controlled by control 13 the 
pressure air in pipe 12 is vented and liquor flows back into the charge 
vessel 11 via run-back through line 19 and RFD 10 and also from tank 16 
via lines 17, 18. During the part of the cycle when the charge vessel is 
venting and filling with liquor, back-syphoning occurs with the direction 
of liquor flow past the sample point being reversed (i.e. from pipe 21 to 
pipe 19) from that in the drive part of the cycle. At the onset of 
back-syphoning, the pressure at the sample point is at a reduced value 
corresponding to the head N of liquor in pipe 21 i.e. decreases to a 
minimum and further evacuation of the sample bottle occurs, but as back 
syphoning continues pressure at the sample point increases because the 
liquor head N decreases and eventually some liquor passing the needle 22 
is drawn through the needle into the sample bottle 24. In general several 
cycles would be necessary to obtain the required sample volume. The pipe 
21 forms a shorter arm of the syphon and pipe 19 a longer arm of the 
syphon. 
With no sample bottle on the needle, any depression is destroyed and air 
inleakage permits the pipework to drain normally by breaking the syphon. A 
pressure transducer 25 is used to monitor pressure variations in delivery 
line 19. The vessel 11 may be vented manually. The cycle could be 
controlled by liquor level sensors 15, 15a responsive to level in tank 11 
and arranged to cause venting or pressurising of tank 11 as the level 
reaches lower and upper limits. 
Some examples are now given. With pipes, 19, 21 at 25 mm internal diameter 
(ID), pipe 21a of 75 mm ID and total length of discharge pipe 21, 21a, and 
a needle 22, 22a of 128 mm length and 0.85 mm ID extending to position C 
FIG. 2 and an RFD drive time of 5 sec, the graphs (a) (b) (c) RFD drive 
pressure (x axis) v sample rate ml/stroke of RFD (y axis) is shown in FIG. 
3 for discharge pipe lengths of (a) 3000 mm (b) 2030 mm (c) 1300 mm, the 
height between the RFD 10 and the sample T-junction 20 being 5400 mm. 
The RFD drive time was varied for condition (b) to give the results of 
Table 1: 
TABLE 1 
______________________________________ 
SAMPLING RATE FOR VARIOUS RFD DRIVE TIMES 
______________________________________ 
Length of Discharge Pipe from 
2030 
Sample `Tee` mm (N in FIG. 1) 
RFD Drive Pressure mbar 
758 
Sample Needle Position 
C 
RFD Drive Time sec 3 3.5 4 5 
Maximum Vacuum in Sample 
166 270 291 289 
Bottle mbar 
Maximum Vacuum at `Tee` mbar 
165 303 312 310 
Sample Rate ml/stroke of RFD 
0.4 1.4 1.5 1.5 
______________________________________ 
FIG. 4 shows a modified T-junction where the needle 22 is 60 mm long and 
0.85 mm ID by 1.24 mm OD with an extension 40 of 75 mm length and 6 mm ID 
extending to position C, below the centre line B of pipe 19 (FIG. 2). 
Results obtained are shown in Table 2. 
TABLE 2 
______________________________________ 
RFD Drive Time 5 
sec 
RFD Drive Pressure 
483 551 621 690 758 827 
mbar 
Maximum Vacuum in 
0 239 239 251 250 239 
Sample Bottle 
mbar 
Sample Rate 0 2.9 3.2 3.2 3.2 3.1 
ml/Stroke of RFD 
Liquor Flow Rate 
116 252 524 491 522 494 
Through Sample 
`Tee` ml/sec 
______________________________________ 
FIG. 5 shows graphs of sample rate ml/stroke of RFD (y axis) v RFD drive 
pressure (x axis) for the needle arrangement of FIG. 2 (graph d) and FIG. 
4 (graph e). 
For reasonable results the lower end of the needle 22 or extension 40 
should be at or below the level B of the mid-line of pipe 19. 
It is evident that the vacuum generated in the sample bottle 24 and the 
sampling rate both increase, with increasing length of discharge line 21 
(N in FIG. 1) from the sample `Tee` 20 and also with increasing RFD drive 
pressure up to 650 mbar, further increases in RFD drive pressure failing 
to increase sample rate. It should be noted that this RFD drive pressure 
is specific to the pipe geometry tested and different relationships may 
apply to other pipe arrangements. The vacuum generated in the sample 
bottle is substantially independent of the point at which the needle 
terminates within the sample `Tee`; however the sample rate is greatest 
when the needle terminates below the center line of the side branch arm 19 
of the angle `Tee`. From Table 1 it is evident that the liquor sample rate 
is increased as RFD drive time is increased up to a time when the 
discharge pipework from the sample `Tee` runs full of liquor; in this 
geometry, 3 sec. Further increase in drive time did not improve the sample 
rate. 
In all cases when the needle terminated at positions A or B, of FIG. 2, air 
was ejected from the needle at some time during the RFD drive stroke. Air 
is ejected for a short period only as the liquor first arrives but then 
air flow is reversed and air is drawn into the liquor stream. This is 
caused by the general pressure fluctuation at the sample tee which takes 
the form shown in FIG. 6. In FIG. 6 the y axis is pressure, the x axis is 
time; the RFD drive time was 5 sec, the RFD drive pressure 758 mbar, 
needle position C. The points on the graphs are K: initial slight increase 
in pressure; L: end of RFD drive stroke and start of back stroke; M: end 
of back syphon, dotted lines D indicate atmospheric pressure. However, in 
considering the pressure curve for the needle it must be remembered that 
pitot effects cause a general reduction in the pressure in the needle 
provided the end of the needle is in such a position as to allow pitot 
effects to work. Thus when the needle is at or below the center line of 
the side arm of the tee then pitot effects prevent a positive pressure 
occurring in the needle. However, when the needle terminates above the 
center line of the side arm no pitot effects are present and the small 
"blip" of positive pressure recorded causes liquor or air to be ejected 
from the needle. When a short time later the pressure goes negative air is 
then drawn into the liquor stream. With the needle terminating at position 
C, of FIG. 2, no air or liquid was ejected at any condition. 
Use can be made of the pressure transducer 25 sited in the RFD delivery 
line adjacent to the sample `Tee` to prove a trace of pressure and vacuum 
during each complete stroke of the RFD. Typical forms of the trace are 
shown in FIG. 6 where it is evident that, with the configuration tested, 
as liquor reaches the transducer 25 a very small positive pressure pulse 
is seen, the pressure then rapidly becomes subatmospheric. At the end of 
the RFD drive stroke and the commencement of the back syphon the pressure 
reduces still further to a minimum and then returns to atmospheric. It is 
suggested that a similar situation exists in the sample bottle. 
Thus, the length N of pipework 21 on the discharge side of the sample `Tee` 
20, returning to the feed tank, influences the sample rate since it 
determines the length of time that liquor is available at the sample 
needle 22 during the back syphon part of the cycle. However, excessive 
lengths of discharge pipe could produce high pressure at the sample `Tee`, 
during the RFD drive stroke, with the danger of liquor ejection from the 
needle. High pressures at the needle could also be generated if the end of 
the discharge pipework is submerged below liquor level in the feed tank. 
When the sample needle terminates at, or below, the center line B of the 
sample `Tee` side arm 19, air bubbles, drawn from the sample bottle during 
evacuation, are carried away from the `Tee` in the liquor flow. When 
however the needle terminates above the side arm, the air bubbles collect 
in the top limit of the `Tee`, position A of FIG. 2, and are drawn into 
the sample bottle at the expense of liquor during the sampling stage of 
the cycle. This effect causes lower sampling rates measured with the 
needle terminating above the side arm of the sample `Tee` than those with 
the needle terminating below it, even though the vacuum generated in the 
sample bottle is approximately the same in each case. 
The increase in sample rate obtained with the 60 mm long, 0.85 mm ID needle 
fitted with a 75 mm long, 6 mm ID extension, over that obtained with a 128 
mm long, 0.85 mm ID needle, is almost certainly due to the reduced 
pressure drop through the increased diameter needle extension. 
The length of pipework on the discharge side of the sample `Tee`, required 
to enable a reasonable sampling rate to be obtained, does not necessarily 
have to be incorporated in the vertical pipe run but could be horizontal 
or formed into a coil if space limitations apply. 
Thus it is possible to use an RFD to provide liquor to a sample point and 
also to evacuate the sample bottle. The position of the sample needle 
should be such that its lower end terminates at, or preferably below, the 
center line of the sample `Tee` side arm 19. The sample rate per stroke of 
the RFD depends on the length of the pipework in the discharge line from 
the sample `Tee`, and also on the RFD drive pressure. Provided that the 
RFD drive time is sufficiently long to ensure that a significant length of 
the discharge pipework downstream from the sample `Tee` runs full of 
liquor, no advantage is gained in increasing drive time. 
Air or liquor was not ejected from the sample needle when the sample bottle 
was absent from the needle, with the RFD drive pressure varying between 
550 and 827 mbar, if the needle 22 or needle extension 40 terminated below 
the center line of the side arm of the `Tee`, and no turbulence or regions 
of high pressure were generated in the sample `Tee`. To this effect the 
geometry of the `Tee` piece should be smooth and free from sudden changes 
of cross-section and the discharge pipework should not be so long as to 
produce high back-pressures at the `Tee`. The discharge pipework should 
terminate at a break pot and not be submerged in the liquor of the feed 
tank, since this can also result in high back pressures with the 
possibility of air or liquor ejection from the needle.