FLUSH BOTTOM VALVE / TANK OUTLET VALVE
Valves used to drain off the contents of a tank or vessel or equipment is termed as (Tank) Bottom Valve.
What does a Tank Bottom Valve do?
â€¢ Provide drainage.
â€¢ Provide Dead space free shutoff.
Which is a Tank Bottom Valve?
â€¢ Any valve serving the purpose.
â€¢ Can be manual or actuated.
Can any Tank Bottom Valve serve the purpose in a BioProcess Equipment? Why?
â€¢ Because, BioProcess is a sterile operation. So, any valve capable of maintaining sterility is to be used. Best choice-Diaphragm Valve.
Can all Diaphragm valves be used? Why?
â€¢ Not always.
â€¢ Because, ordinary Diaphragm valves when mounted in a vertical or angled position will have the content (media or Fermentation Broth) of the tank till the diaphragm. This creates a dead leg, a very serious issue in BioProcess.
â€¢ But this valve can be used in places where the sterility is not very critical (Media preparation vessels, Buffer formulation vessels and other preparation vessels wherin the contents of the tank may either be sterilized in the next process or will be filtered using a 0.2 Micron filter.
â€¢ Sometimes, steam is connected to this type of valves and sterilization is done before the harvest.
â€¢ A valve which perfectly seals the opening in the vessel and has the capability of being sterilized independently before the harvesting of the vessel contents.
This questions and answers lead us to a new Kind of valve called Flush Bottom Valve.
â€¢ The valve is normally welded to the bottom most portion of the bottom dish. The term Flush comes because the valve body is flush welded to the vessel dish.
â€¢ Though many types of FBVâ€™s are available, the diaphragm type is more commonly used.
â€¢ The valve is independently Steam sterilisable.
Diaphragm Flush Bottom Valve – Working Principle:
The three steps shown in the picture is explained.
1. Contents are removed (Diaphragm in open position)
2. Valve shuts down (Diaphragm in closed position)
3. Steam enters and cleans the valve internals
FBV in Bottom driven Vessels:
In case of bottom driven agitators which are present in the centre, the FBV finds a place just adjacent to the agitator and the consideration is that there should be no dead leg inside and drainability should be 100%. And this is achieved by the perfection of the fabrication department.