Leak on purge valve when opened with zero flow

[jcharoen]

We have a problem with our semi-prep pump Thermo Fisher Ultimate 3000 series HPG3200-BX. Even with zero flow set, when we open the purge valve, there's a constant flow of solvent out of the valve. The flow seems to be because of gravity as when we heightened the tubing, the flow slows down. The fastest out is about 12 mL/min. Note that the maximum flow rate of this pump is 50 mL/min. What could cause this to happen? Thank you.

[vmu]

https://assets.thermofisher.com/TFS-Ass ... ration.pdf
Page 61
HPG-3200BX
To prevent the solvent from flowing through the pump fluidics when the pump flow is zero, close the shut off valve on the solvent supply line when the pump is not delivering.

For your pump, this gravitation-driven flow is normal even when the purge valve is closed. A special shut off valve (page 233, P/N 6042.2531) is needed to prevent this.