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.