Tank Venting and Air Filtration
Hydrophobic sterilizing-grade filters are commonly used as air vents on processing tanks. The goal of the application is to maintain near ambient pressure in the tank while ensuring sterility in the tank. The tank vent filter removes viruses and microorganisms from the gas as it flows in or out of the tank.
Filter requirements
- Sterilizing-grade PTFE membrane
- Integrity testable, bacteria and virus retentive
- Robust construction validated for multiple SIP cycles
- Delivers high flow rates
- 100% integrity tested to ensure quality
Sizing Your Vent Filter
Air flows in and out of a process tank for two reasons. The first is to replace a volume of liquid as it is pumped in or out of the tank. Sizing the tank vent filter for pump-out or fill rate is relatively simple. The air flow rate will be equal to the pump-out or fill rate. With flow rate and pressure determined, a flow/ΔP curve can be used to determine sizing.The second reason air will flow into a process tank is to compensate for the volume change associated with steam condensation. At the end of a tank steam-in-place procedure, steam in the tank will cool and undergo a phase change to liquid water. There is over 1,000X difference in volume between an amount of water in gas phase vs. liquid phase. During cooling, sterilized ambient air must be allowed into the tank to prevent vacuum. Sizing the vent filter for steam collapse requires knowing the vacuum rating of the tank and the convective cooling rate. These can be calculated based on the tank dimensions including height, diameter and wall thickness. Millipore has developed a computer program to facilitate these calculations.
Improper tank vent sizing can result in low pump-out rates, loss of sterility due to rupture disk or filter failure, or worst case, tank implosion. Fortunately, proper sizing is not difficult as long as the flow requirements and driving force are understood.
