Are there any suggestions or tips on troubleshooting flow problems on the Lachat QC8500 FIA instruments?


Dokument-ID TE7662


Veröffentlichungsdatum 23.10.2019
Are there any suggestions or tips on troubleshooting flow problems on the Lachat QC8500 FIA instruments?
Tips on troubleshooting flow problems
Information on common causes of flow problems and instruction on isolating where the concern lies.

Confirming a flow issue – Once a flow issue is suspected or realized it is recommended that all reagent lines be placed in water. It is important to understand that a flow issue is present if there is a lot of backwards movement in a line or no movement though the line. This can be determined by pulling the transmission line of concern out of the water/reagent to draw some air. The movement of the air slug can then be observed. Some lines will move forward then stop, forward then stop. If the movement is predominately forward this is not necessarily an indication of a flow problem.

Pump tube concern - If a line is showing significant backwards movement or no movement at all, one should verify that pump tubes have been recently changed. If pump tubes are worn they may not flow properly. It may be worthwhile to unclamp pump tubes and clamp them down again just in case one or more pump tubes did not seat properly.

Waste line concerns - Waste lines are a common source of flow issues. It is not uncommon to think the waste line is not important since it is just for the waste. However, all flow must ultimately move through the waste line so they are very important. If a waste line is dirty, submerged in waste, or travels too far (dead volume) it can cause back pressure and contribute to flow issues. The user should also make sure waste lines drop straight down from the instrument. If the waste container is placed at the level of the instrument or above, it will also add back pressure. The waste line can be ruled out or confirmed as an issue by checking if it contributes to the issue by detaching the waste line and letting the waste drip into a beaker. If flow improves when detaching the waste line, it is contributing. The waste line can then  be trimmed, replaced or laid out differently depending on the exact concern.

Tracing the flow problem – If the source of the flow issue is not apparent there is a simple method to isolate where the concern is located. The concern may be a clog in tubing or component or crimped tubing. By systematically disconnecting connections one can determine where the flow issue is located. It may be helpful for the user to have the manifold diagram to look at while doing this. Once tubing is disconnected from a specific spot, the user can pull the line with the flow problem out of the water to draw a slug of air. If it flows well, it means that things are OK up to the point from which the line was disconnected. If it does not flow well, it means the problem is prior to the point from which the line was disconnected.

For example, if the user disconnects before a specific mixing coil and flow looks good but when they disconnect after the mixing coil flow does not look good, there is an issue with the mixing coil. This would likely be a clog or crimp in the tubing around the mixing coil. If the user systematically disconnects from various points and continues to check the transmission line of concern, they should be able to isolate the location of the issue. 

Working from the back end (starting with the waste line) and moving forward can be more efficient. Whenever disconnecting before the problem, it may take a couple of minutes for the flow problem to develop again. If disconnecting after the problem, the flow issue will still be present and the user can move forward to the next spot right away. If disconnecting before the problem and the flow problem goes away, the user will need to wait until back pressure builds up to the point that they can see the flow struggling again, before they can move on the next spot.

Carrier and sample line – For problems with flow through the carrier and/or sample lines, a good place to check first is before and after the injection valve. It is possible to get a clog at the injection valve. To try and resolve a clog at the injection valve see the article on What can be done if a Lachat valve seems to be clogged or flow is not smooth through the valve?

Sample line – For problems with flow through the sample line, another good place to check is the dilutor valve if the system has a dilutor. This can be done by using a piece of tubing to bypass the dilutor. If a piece of tubing is run from the sampler probe to the sample line pump tube in place of the tubing that goes through the three-way dilutor valve, the dilutor valve will be bypassed. If this resolves the flow issue the problem is with dilutor valve (or one of the two lengths of tubing attached to it.  To try and resolve an issue with flow through the dilutor see the article on What can be done if there is a problem with flow through the Lachat PDS200 dilutor?


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