Hydrophobic vent filter

Of course, the opposite phenomenon occurs with hydrophilic liquid filters where air bubbles are present in the liquid process stream it is called "air-binding". Often a hydrophobic vent-filter will be used in conjunction with the main hydrophilic membrane filter to allow escape of accumulated air without permitting liquid leakage. 

Other applications of filters include sterilization of venting or displacement air in tissue and microbiological culture (carbon filters and hydrophobic membrane filters) decontamination of air in mechanical ventilators (glass fibre filters) treatment of exhausted air ftom microbiological safety cabinets (HEPA filters) and the clarification and sterilization of medical gases (glass wool depth filters and hydrophobic membrane filters). 

Pipework systems, valves and vent filters should be properly designed to facilitate cleaning and sterilization. The use of clean in place and sterilize in place systems should be encouraged. Valves on fermentation vessels should be completely steam sterilizable. Air vent filters should be hydrophobic and validated for their scheduled lifespan. 

Water storage tank vent filters must be equipped with a sterilizing air filter in order to prevent the air, which displaces water drawn from the tank, from microbiologically contaminating the water. The filter must be hydrophobic in order to prevent condensation from blinding the filter and preventing air entry or escape from the tank. It also must have a mean porosity of less than 1 pm. 

PTFE membranes are highly hydrophobic and, therefore, are used as air filters. Air filters have to be highly hydrophobic to avoid water blockage due to moisture or condensate, especially after steam sterilization of these filters. Water blockage could be detrimental, if the filter is, for example, used in a tank venting application to overcome condensation vacuum of a non-vacuum resistant tank. If the filter would not allow a free flow of air into the tank, it may implode. Therefore, vent filters for this application have to be chosen and sized with care. PTFE membranes are also highly mechanical and thermal resistant, which is required, because such filters are used over several... 

WFI storage tanks are equipped with hydrophobic bacterial retentive vent filters. 

In the case of air-vents, even if the filter has been sized adequately to handle the passage of air commensurate with liquid filing and withdrawal rates, the use of hydrophilic filters has caused the implosion or collapse of more than one storage tank. A hydrophobic filter passes air preferentially indeed, a water intrusion pressure is required to force water into the pores. 

The overpressure relief containment system (see detail in Figure 12.5) uses a stainless steel vent stack (4 inch diameter pipe) to the roof of the building. It is terminated by an oversize hydrophobic filter. Calculations indicate that, in the event of a burst, the volume of liquid that will be discharged can be accommodated in an extension (ca. 10 feet long) of the vent stack below the discharge point. This accommodation is necessary to... 

The treatment so far has focused essentially on microfiltration and cake filtration of a liquid feed. However, microfiltration of process gas streams, as well as gas flowing through vents on tanks, containers, fermentors, etc., are also quite important in the deadend mode. Generally these filters are made of hydrophobic materials like PTFE, PVDF, PP, etc., so that water does not wet the pores and gases can easily flow through the filter pores. 

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