Pressure instability is a common fault in high pressure liquid chromatography ( HPLC ), and its performance is: 1 pressure gradually changes (rises or decreases) over a period of time; 2 The pressure changes instantaneously ( >3kg ). The reasons for summing up are nothing more than the following four situations: (1) There are bubbles; ( 2 ) Leakage; ( 3 ) The check valve is defective; ( 4 ) The pump is not working properly. For the case of 1 : it usually appears in the period of starting up, often the mobile phase is not well balanced in the liquid chromatography column , and the temperature of the oven is not constant. These are not instrumental problems, as long as they are balanced for a while, they will be stable. If a gradient program is used, the pressure will follow as the ratio of the mobile phase is changing. For the first case â‘¡: by analyzing the following steps, you can quickly determine the cause. Firstly, the bubble factor is eliminated: the bubble is generated because the air is dissolved in the mobile phase, and the air will be separated under the action of the pump pressure. The air bubbles will not be discharged in the pump body, which will not only affect the accuracy of the flow, but also the pump pressure. Stable, then we only need to open the exhaust valve, and use the quick flush function to quickly drive out the air bubbles. To prevent the generation of bubbles, a good way to use it is to use an online degasser. When there is no degasser, the mobile phase is degassed. Ultrasonic vibration is a commonly used method for removing bubbles. Although it is simple but not effective, it is advisable to filter the mobile phase twice with a microporous membrane and use the negative pressure of the vacuum pump to release the air dissolved in the mobile phase. Better. If we find that there are tiny bubbles in the infusion tube connected to the filter head, it means that the filter head has a blockage and must be cleaned. You can use 10 % nitric acid for 15 minutes. If there are bubbles, then change it. New filter head. Secondly, it is necessary to check whether there is liquid leakage in the liquid chromatography infusion pump. Generally, the leakage of the pipeline connected to the pump will lower the pressure and have little effect on the pressure stability. If the plunger or plunger rod in the pump is worn out, it is not the same. It is not only in pressure, but also in large changes and insufficient flow. As long as the pump head or the flushing tube is leaking (the liquid level will rise when there is a flushing bottle), there is definitely a problem with the plunger pad or plunger rod. The third is that the one-way valve is defective. When contaminants such as salt or impurities adhere to the surface of the ball and the valve body in the check valve, the sealing performance is destroyed, and the one-way performance of the infusion is lowered. Although the pump is working, It is to transport poor liquid, and it can not be infused when it is serious. Reflected in stress, it is characterized by severe instability or no pressure. At this point you can remove the check valve and ultrasonically clean it with isopropyl alcohol for 20 minutes. If there is salt, it will be better to use ultrasonic cleaning with hot water. If the requirements are not met after cleaning, the check valve can be connected to the flow path and flushed with a large flow of isopropyl alcohol. The structure of the check valve is relatively fine. If you are not sure, do not disassemble and clean it. When using ultrasonic cleaning, pay attention to the position of the valve to prevent the component from oscillating. Otherwise, the effect will not be satisfactory after assembly. When the ball in the check valve is damaged, it is only replaced. After zui, there is a situation that causes pressure instability, that is, there is a problem in the phase of the pump operation. This situation occurs less and can be solved by adjusting the initial position of the pump. The above four aspects basically include all the reasons for the unstable pump pressure. For most users, as long as they follow this line of thinking, the general fault can be solved. Biological Glue,Histoacryl Bio Glue,Bio Glue Safe Surgical,Cyanoacrylate Bio Glue Shaoxing Aladdin Enterprise Co.,Ltd , https://www.xhemostat.com
Maintenance example 1
    Model: LC-10ATVP pump
Overhaul process:
   1 First open the drain valve, use the purge function to remove air bubbles from the pump body, observe the infusion tube, and found no air bubbles. Close the drain valve and run the pump at a flow rate of 1 ml/min . Check that the pressure is still unstable, so that it is confirmed that there are no air bubbles in the pump and the filter head is not contaminated.
   2 Observe that the pump head and the cleaning pipeline are not leaking. Close the pump outlet with a plug and run the pump at a flow rate of 0.2 ml/min . The pump pressure will rise all the time, and the pump will be stopped after reaching the high protection pressure of Zui. It can be concluded that there is no wear on the plunger rod or the plunger pad.
 3 Check the check valve.
 4 Check the initial position of the pump and find that the position sensor changes again. After adjusting the distance between the light coupler and the lever, the fault is eliminated.
Maintenance example 2
 Model: LC-20AT double pump high pressure gradient unit + mixer
 Symptoms: The pressures of the two pumps A and B are stable when they are operated separately; as long as the pressure of the double pump is turned on, the pressure is unstable, and the higher the pressure value, the greater the fluctuation.
Overhaul process:
 Preliminary judgment that the fault is strange, the pressure change is small when the pump is running alone. It seems that the fault should not be on the pump, it will be transferred to the mixer, the mixer will not block or leak, take another instrument and try it. No problem. . Check the check valve. In order to confirm which valve is the problem, the ultrasonic cleaning method is adopted. When the check valve check valve is cleaned, the problem is solved. There are two gem balls in the check valve. If both spheres are polluted, this valve basically loses the one-way effect. Now only one ball is polluted, so it will show a little instability at high pressure. When a double pump is used, the pressure of the A pump is affected by the valve that is not tightly closed to the B pump, which exacerbates the pressure change.