Chromatography Forum

I've tried to calibrate the seal pack for a Waters 717 plus LC autosampler, nkg had helped get past the first hurdle which was getting the pressure between 400-600 psi for the seal pack adjustment process to ensue on my autosampler. Now I'm getting the message "top sensor too low".

Hi,

When you rebuilt the seal pack and replaced the needle this can sometimes happen due to the needle ferrule been in a slightly different position. You need to adjust the sensor until it passes the adjust seal setup.
Which type of injector have you the old or new style. The old style is gold in colour and the new is silver in colour. This is for an Alliance. If it is a 717 autosampler then it is gold in colour. There will be an adjustment screw on the top of the bracket which holds the sensors, there is a spring under it for tension. You just loosen the bottom locking screw and then adjust the sensor heights until it passes. If it doesn't pass then it is more than likely the seal pack is at fault.

Regards,
Bull76

I have a waters 717 plus autosampler for the LC, the adjustment screw seems to be silver in color and for some reason it's tainted with blue paint. There isn't any bottom locking screw so I've adjusted the screw so that the injection needle is pushed up and down. If I adjust the screw excessively clockwise, the platform will move up and will read "top sensor too low", if I screw clockwise till the screw is about to come off it'll give me a "pressure not in range" message.

By "top sensor", is it referring to the sensor that senses the position of the injection needle i.e. designates the inject and non-inject positions?

quick start point for the sensor bracket is that you should just be able to get a 5/16 union between the bracket and injector where the spring is. when adjusting the bracket, only do it by quarter / half a turn at any time and then see what results you get by doing the seal pack adjustment.the blue 'paint' applied twas just o stop the screw moving after adjustment had been carried out

thanks, will take that into account. Do you have any advice on what measures to take when getting the message "cannot find upper seal" during the seal pack adjustment? I called waters and they suggested several things

1)check to see if there's liquid on the top of the vial caps as this may be a sign of a worn out seal.

2)use a higher flow rate.

3)adjust the level of the injector with respect to the sensor once again, in smaller increments.

4)observe the type of vial caps and see if they're the waters brand, find better caps if necessary.

Any other suggestions to this would be greatly appreciated. At this point, it seems that I've got a worn out upper seal. When I first opened up the autosampler, it was discovered that the previous Waters technician didn't screw on the injection platform, my guess is that the poor alignment and possible injections to the more concrete peripheries of the vial caps may have worn out the seal caps. Not certain how to describe these seal caps but they're the ones where you pop them on to the glass vials which are about 1.5 inches in length (the glass vials that is) and they're definitely have more tensile strength then those teflon caps.