DE10008623A1 - Automatic effluent water sampler draws sample to a pre-determined level within sample holder then brought to a given level by compressed air - Google Patents

Abstract

Automatic liquid sampler sucks a liquid dose into a vessel (1) in which the level is automatically brought to a pre-defined level (5). Fluid is then expelled over an overflow by the introduction of a given volume of compressed air, leaving a given residual volume of fluid in the sample holder (1). Any required sample volume may be selected whose volume is below that of the pre-defined level (5). The volume of air required to displace the excess sample volume is automatically determined by the period of pump operation or pump operating speed.

Description

The invention relates to an automatic sampling system according to the vacuum principle, in which the dosage can be changed automatically.

In many cases, there is an automatic sampling of water and waste water Requirement to control the sampling depending on a flow measurement. This means, that at a high flow rate more sample liquid should be taken and at low flow rate correspondingly less.

So far, this has been achieved in such a way that a volume of e.g. B. 50 ml is removed, the sampling frequency being adapted to the flow signal. Sampling devices available as standard are capable, depending on the sampling point, to a maximum take a sample every 2 minutes. This has the consequence that when things change a lot Flow of z. B. 1:20 a sample is taken every 40 minutes at low flow.

However, since pollutants may also be present at low flow rates Subsequent examination of the samples may be of interest, these are also important Sampling phases as often as possible. At an interval of 40 minutes, however, that is The risk that such pollutant discharge is not recorded is relatively high.

To avoid this problem, a sampling device is required, which is in constant sampling intervals of z. B. takes 5 minutes of samples Individual volume is adapted to the respective flow signal. To the above In order to cope with flow fluctuations, the volume of the individual samples must change by 1:20 to be possible.

There are already devices on the market with which this flow-dependent sampling is possible. These are devices that work with a peristaltic pump, but only the number the pump revolutions is adapted to the current flow signal, which leads to proportional change in sample volume leads.

Since in Germany and the rest of Europe mainly sampling devices Vacuum system used is a flow-dependent sampling based on this pneumatic system is desirable.  

Here, too, there is a system on the market in which the sample liquid is vacuumed into one Dosing vessel is sucked in. The desired amount of sample is set here through an overflow pipe in this vessel, which is adjusted in height by a motor. If this The overflow pipe is moved to the lowest position, most of the removed runs Sample back to the sampling point and only a small part of about 20 ml dosed. In the uppermost position of this overflow, about 250 ml dosed. This system partially meets the requirements set out above, but has fundamental disadvantages.

• - Very high mechanical effort
• - technically vulnerable
• - moving and to be sealed Parts in the liquid (waste water!)
• - expensive to manufacture
• - Setting range too small (only about 1:10).

In order to meet the requirements mentioned without the disadvantages mentioned, an extraction system is required that meets the following basic requirements:

• - working pneumatically, d. H. Suck in the liquid with Negative pressure in a dosing vessel
• - automatic adjustment of the sample quantity without Moving parts in the liquid
• - Volume setting range greater than 1:20
• - easy to manufacture
• - reliable (low wear)
• - inexpensive

The basic idea of the invention is to use a relatively large vacuum system To convey sample amount into a dosing vessel, there to a reproducible maximum amount level, and then pump in so much of a precisely defined amount of air Squeeze out liquid so that the desired amount of sample remains in and in the sample container can be dosed.

One problem with this is that the maximum amount can be exactly increased after the suction process level without environmental conditions such as suction height, hose length and Diameter, viscosity of the liquid etc. influence the accuracy.

Another difficulty is the exact adjustment of the sample volume, which means that precisely measure the amount of air delivered to displace the liquid that is not required and that the drainage of this liquid can take place unhindered.  

The object is achieved according to the invention with the features from characteristic part of the protection claim 1

The conveyor and metering device of the automatic metering unit consists, as shown schematically in Fig. 1, of a metering vessel ( 1 ) with a drain valve ( 7 ) and an inlet line ( 4 ). In the upper part of the vessel there are two level electrodes ( 2 ) and an air connection ( 3 ).

The supply of pressure and vacuum takes place via the pump ( 8 ) and a switchover device ( 9 ).

A ventilation opening with hose and ventilation valve ( 12 ) is attached to the inlet line.

The procedure for taking a sample with automatic volume adjustment and dosing is as follows:

• 1. The drain valve ( 7 ) closes
• 2. The switching device ( 9 ) is put under pressure
• 3. The pump ( 8 ) switches on.
  The metering vessel ( 1 ) is thus pressurized with compressed air via the air connection ( 3 ).
  This pressure can only escape through the riser pipe ( 6 ) and the suction hose ( 4 ), which leads to the blowing of this hose.
• 4. Then the switching device ( 9 ) switches to vacuum. A vacuum is created in the dosing vessel ( 1 ), which leads to the suction of liquid from the tapping point ( 11 ) via the suction hose ( 4 ) into the dosing vessel ( 1 ).
• 5. As soon as the liquid in the metering vessel ( 1 ) has reached the level electrodes ( 2 ), the pump ( 8 ) switches off and the ventilation valve ( 12 ) opens.
  This causes the liquid in the hose ( 4 ) to run from the overflow edge ( 5 ) back to the tapping point ( 11 ).
  Since there is still negative pressure in the upper part of the dosing vessel ( 1 ), no further liquid is removed from the dosing vessel during this process and the water level remains above the overflow edge ( 5 ).
• 6. After a short settling time, the changeover valve ( 9 ) switches to ventilation, which causes the liquid level in the dosing vessel ( 1 ) to automatically level to the overflow edge ( 5 ). The excess water runs off through the suction hose ( 4 ). In any case, this results in a precisely reproducible maximum volume, which is determined by the overflow edge ( 5 ).
• 7. After leveling, the changeover valve ( 9 ) switches back to pressure.
• 8. The pump is switched on at a reduced speed until the desired volume of air is pumped into the metering vessel ( 1 ).
  The air volume is determined either by the running time of the pump or by the number of revolutions.
  Pumping air into the metering vessel ( 1 ) causes exactly the same amount of liquid to overflow over the overflow edge ( 5 ) and the suction hose ( 4 ). The desired amount of sample that should remain in the dosing vessel can thus be set precisely.
• 9. After a further brief settling time, the drain valve ( 7 ) opens and the sample runs into the sample container ( 10 ).

Fig. 1

Fig. 1 shows the sampling system in a schematic representation in the rest position. The drain valve ( 7 ) is open, the changeover valve ( 9 ) is on ventilation and the ventilation valve ( 12 ) is closed.

Fig. 2

Fig. 2 shows the sampling system in the suction stage. The drain valve ( 7 ) is closed, the changeover valve ( 9 ) is in vacuum, the pump ( 8 ) is running and the ventilation valve ( 12 ) is closed.

In this illustration, the dosing vessel is already half full, i.e. H. the suction process is still running.

Fig. 3

Fig. 3 shows the sampling system after the water level in the metering vessel ( 1 ) has already reached the level electrodes ( 2 ) and the ventilation valve ( 12 ) has opened.

The drain valve ( 7 ) is closed, the changeover valve ( 9 ) is on vacuum, the pump ( 8 ) is off. The suction hose ( 4 ) is already empty. The liquid in the riser pipe ( 6 ) is thus up to the overflow edge ( 5 ). The liquid level in the dosing vessel ( 1 ) is slightly above the overflow edge ( 5 ), since there is still negative pressure above this liquid.

Fig. 4

Fig. 4 shows the sampling system after leveling.

The drain valve ( 7 ) is still closed, the changeover valve ( 9 ) is on ventilation, the pump ( 8 ) is off and the ventilation valve ( 12 ) is open.

By venting the interior of the metering vessel via the air connection ( 3 ) and the changeover valve, the excess water runs down to the overflow edge ( 5 ) via the suction hose ( 4 ). An exactly reproducible initial volume of sample liquid is thus set.

Fig. 5

Fig. 5 shows the sampling system in setting the desired amount of sample. The drain valve ( 7 ) is closed, the changeover valve ( 9 ) is under pressure, the ventilation valve ( 12 ) is open and the pump ( 8 ) is running at reduced output. Pumping in air causes the liquid in the metering vessel ( 1 ) to be pressed down and overflows via the riser pipe ( 6 ), the overflow edge (S) and the suction hose ( 4 ).

Fig. 6

Fig. 6 shows the sampling system after reaching the desired amount of sample. The drain valve ( 7 ) is closed, the changeover valve ( 9 ) is on ventilation, the ventilation valve ( 12 ) is open and the pump ( 8 ) is off. The liquid level is now exactly at the desired level.

Fig. 7

Fig. 7 shows the sampling system when dosing into the sample container. The drain valve ( 7 ) is open, the changeover valve ( 9 ) is on ventilation, the ventilation valve ( 12 ) is open and the pump ( 8 ) is off.

The set sample volume now runs into the sample container ( 10 ).

Claims (3)

1. Automatic sampling system for liquids, characterized in that the sample liquid is sucked into a metering vessel ( 1 ) by negative pressure, is automatically leveled to a fixed level ( 5 ) in this vessel and then by injecting a certain amount of air so much liquid over a Overflow is displaced so that a desired smaller volume of sample liquid remains in the metering vessel ( 1 ) and can be filled into a sample container ( 10 ). This means that every sample volume whose level is below level ( 5 ) can be set automatically. 2. Sampling system according to claim 1, further characterized in that the Air volume necessary to displace the unnecessary sample volume by the Change in the running time of an air pump is determined. 3. Sampling system according to claim 1, further characterized in that the Air volume necessary to displace the unnecessary sample volume by the Change in the number of revolutions of an air pump is determined.