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I have a "Micropump GB-P25.JVS.A" gear pump. I pump in the range between 100 and 500 ml/min up to a column about 10 cm above the pump level. The column is filled from the top and has a bottom outlet.

I have noticed lately that my pump allows the fluid to flow backwards when it is not on. I assume this is caused by the small pressure head caused in the column. The backflow is small, but it is there. This was not the case a couple of months ago.

Furthermore, one can forcefully pump the fluid from the inlet side of the pump using a syringe.

I suspect that either the gears or the O-ring are damaged.

Are there any other possibilities I might be missing?

How hard is it to change an O-ring of this kind of pump?

Are there any other possible fixes to the situation? I have attached check-valves before and after the pump, but I doubt this is the ideal solution.

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  • $\begingroup$ Please show the type of pump - if it is similar to the one I am thinking of, then there is a face to face seal and the o-ring is for the case... $\endgroup$ – Solar Mike Sep 18 '18 at 14:15
  • $\begingroup$ @SolarMike the pump is a "Micropump GB-P25.JVS.A" gear pump. Specs can be seen here www.micropump.com/support_documents/Series_GB_Technical_Specs.pdf $\endgroup$ – Keine Sep 18 '18 at 14:20
  • $\begingroup$ So no more info ie diagram or link etc to material in the original question. $\endgroup$ – Solar Mike Sep 18 '18 at 15:59
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You will probably need to install a check valve (or manual valve) to prevent the backflow, and rebuild the pump heads periodically. Over time, the gears wear down and small gaps form. This both leads to reverse flow when the pump is off and reduces the liquid flow rate for a given pump speed.

I used to work at a plant that used gear pumps that look similar to the one you have. When the pumps were in service, they were used continually, but when out of service they were manually valved out to prevent backflow like you describe. The pumps were connected to a flow meter and VFD to maintain the same flow rate despite pump wear. Additionally, we rebuilt the pump heads periodically (yearly if I remember right). I'm pretty sure the manufacturer sold rebuild kits for that purpose.

Side note: Eventually, we switched to peristaltic pumps which were much easier to control and maintain.

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