By Jon Stewart on Monday, June 14, 2004 - 03:36 pm:

I am having a weird problem with my Beckman 126 pump and would be grateful for any help. The system is running System Gold software (the old VDI version) and is being used for reversed-phase analysis (water-acetonitrile). The problem is that the pressure read-out for both A and B pumps are 4-5 fold higher than they should be for every column in my collection. For example, a brand-new C18 column that gave a very normal backpressure of 600 psi (100% acetonitrile, 1 mL/min flow rate) on a Gilson system displayed 2500 psi on the Beckman instrument under the same conditions. When connected to the Beckman system, both the A and B read-outs give essentially the same pressures, and the same high pressure readings occurred even when I connected the outlet check valve directly to the column (by-passing the mixer, pulse damper, filter and injector). On the other hand, when no column is connected, the backpressure is essentially zero. I'm about out of ideas at this point. Has anyone else ever seen anything like this or have any suggestions of where to look?

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By bill lyons on Tuesday, June 15, 2004 - 12:35 pm:

Hello Jon,
Inspect the filters on the discharge (top) check valves.Those pumps used an arrangement such that the pressure reading is actually a measurement of the current the pump motor draws against the restriction. When the seal sheds material over the years,the filter will block and the motor current increases.
It might also be that a recalibration of the pressure readout is necessary,because of aging of components such as the motor.

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By Maria on Wednesday, June 16, 2004 - 01:30 am:

Perhaps if you work with salts, a little "stone" is installed in the tubes. TO remove salts, you must past acid water (with no salts, pH 3), to sissolve them. But the most probable fact is that it is the filters in the pump.

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By henrik on Wednesday, June 16, 2004 - 12:18 pm:

When you say pump A and B do you mean to diffrent system or is it one high pressure system?

Also check the flow