Air in dosing lines

[miller75]

I have got hold of a used KH director and have been using it for a couple of months now, it seems to be working fine but I have noticed that in the line for the sample water always seems to have large air bubble in it.

I assume this is going to affect the accuracy so wanted to get rid of them but I cant see where they are coming from, would a worn dosing head allow the water back siphon back into the sump? Would there be any issue adding a none return valve to stop the siphon?

 

[Lasse]

The last action of the KH director is to empty the sample tube. After an analyse is the sample tube total empty - including the filter - no water - only air. When a new analyse start - pump 1 (sample tube) fill up the sample line and a part of the sample chamber. Next step is that pump 2 empty the sample chamber and after that pump 1 fill the chamber to the decided volume. In this way - its always guaranteed fresh samples. This means that you can sometimes see air in both pumps (1 and 2) suction tube

Sincerely Lasse

 

[Lasse]

Would there be any issue adding a none return valve to stop the siphon?

Do not use a none return valve to the sample tube. It should be empty after an analyse

Sincerely Lasse

 

[miller75]

Do not use a none return valve to the sample tube. It should be empty after an analyse

Sincerely Lasse

Thanks Lasse. I do see air in the lines on the second fill of the chamber and to be honest its quite a lot, the air bubbles are about 10mm (1/2 inch) in length and are continually going through.

I will double check the length of the sample pipe and recalibrate the pumps just in case its pulling the correct amount through on the first pass

 

[Lasse]

If you have a filter in the sample tube line - activate add filter volume. I also measure the sample input tube and add the length of the pump tube (normally around 11) cm and also add the length of the tube between the pump and the KH director. When I get a steady result I do a test with my alternative methods (Hanna and Salifert) and - if necessary use the percent calibration

Sincerely Lasse

 

[miller75]

Thanks Lasse all sorted now, recalibrated everything and the air bubbles are gone