Venting applications require careful management of condensate on the vent filter to maintain a sufficient level of gas flow, not only during use, but also during steam sterilization. Water vapor can condense on a vent filter membrane during use if the fluid in the tank is water based and the temperature of the filter is lower than the dew point of the fluid in the tank. 

In most applications the fitting of a heating jacket will resolve this issue by maintaining the temperature of the vent filter and housing slightly above the dew point of the liquid in the vessel. This should prevent the formation of condensate on the filter, thus preventing the filter from blocking and being damaged due to excessive differential pressure. 

To avoid filter blockage on hot WFI storage tanks, the filter must be removed and brought back to our lab where we carry out a reverse bubble point test. The results of the reverse bubble point test can confirm filter failure by extensive bubbling @ 150mbar.

The lab deconstructs the filter for further inspection. If the pleat pack has collapsed, the membrane can be damaged. This indicates that the max differential pressure has been exceeded in the reverse flow direction, and indicates that the filter has been blocked. This confirms that the pressure when filling the tank exceeds the design operating parameters of the filter, causing the filter to fail.  

We believe condensate is able to penetrate the pores of the drainage layer and possibly even the membrane. Vapour at 90°C has a much lower surface tension and makes wetting of a hydrophobic membrane a lot easier. The wetting of the membrane creates enough of a blockage to exceed the max differential of the filter, thus damaging the membrane and affecting the integrity.  

Hall Pyke’s solution is to use our COR-PFA filter, which has an all fluoropolymer construction. We install our filter and carry out water intrusion tests every 4 weeks, for six months, to ensure there are no more failures. 

For more information on ways to prevent vent filter integrity test failures on hot WFI storage tanks, get in contact with a member of the team today on +353 1 4501411 or email us at info@hallpyke.ie.