Hello everyone,
My question is about the flow exceeding the set value in the Knaver HPLC pump. By setting the flow pump to a specific value and opening the pressure relief valve, the flow output from the pump is much higher than the set value. The output value is close to the value that the purge button is pressed for bubble removal. This amount does not change with the change of flow.
I would be grateful if you could help me find out what the problem is.
HPLC pumps are positive displacement pumps. They should deliver a constant flow rate up to the rated pressure. As seals wear, the flow rate will drop as the back pressure goes up and need replaced. Getting a flow rate higher than rated is only possible if the electronics are miscalibrated or the pump head is over-sized for the unit. You can always manually recalibrate the flow rate. Note, depending on the pump design, you might (I emphasize might) get some siphoning from the reservior when there is no backpressure on the pump. You can check this by locating the reservoir at different heights and measuring the flow rate.
This might be occurred due column inefficiency. At first the column used in the HPLC need to be checked whether there will need a guard column. Otherwise the suction pump have to be checked.@ Luke V Schneider
Md. Akbar Khan He was claiming the flow rate was high and when the column by-pass was used. A blocked column makes the flow rate low.
Mahdiyeh Hj wrote "and opening the pressure relief valve":
- NOTE: Pump testing / operation should be done with the pressure relief valve CLOSED. If the pump is siphoning liquid from the bottles (overhead), then liquid may stream through the line at a high flow rate. HPLC pumps are not designed to be used by running liquid through the relief valve (which is for purging solution only).
Unless the pump has been tampered with (calibration off), it should not output a higher flow rate than indicated. After properly purging the pump for use, Verify actual flow rate (on each channel) by running the pump with pure water under suitable back-pressure (e.g. 40-bars) using a restriction line, then measure the volume obtained over time, at a set flow-rate (e.g. 1 mL/min for 5 minutes should = 5 mL volume in a graduated cylinder).
Have you tried calling Knauer technical support for the proper way to determine flow rate performance verification? Is your pump configured with or without a pressure sensor? Based on your details, it does not sound like you are measuring flow rate correctly. Luke V Schneider is correct and performing pump troubleshooting maintenance incorrectly could become a qualification nightmare. If you are truly experiencing variances in the pump flow rate then you to: 1) Clean the ball valves 1st, 2) try exchanging the ball valves 2nd, 3) purge the pump head to remove the air bubbles, or 4) tighten the inlet screw 1 and outlet screw 1 on the pump head with a torque wrench and 15 Nm (pump head with ceramic inlays: 8 Nm).
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