 In this module, we will talk about the seal and the o-rings that is very important while designing and while making the fermenter. Not only in the designing and fabricating of the fermenter but also they are very important in the operation of the fermentation process. So when we talk about the construction material either that will be the glass either that will be the stainless steel. So there is a different joints and there will be a contact from the outside environment to the inside of the fermenter vessel. So as concerned the seals and the o-rings because as we have well aware about the fermentation process that should be in a septic condition and that should be having a specific containment regulations. So as concerned the seals either that concern because when there is agitation system and we will talk about agitation system or agitator in the later modules but we see when there is agitation as we have talked about the single impellers and the multi impellers then there should be a shaft and there should be a motor over that. So when there will be a mixing mechanism then there should be a mechanical stirring. So we should have a very reliable seal that can give us a surety of no way enter of the contaminants from the outside to the inside of the fermenter and as well as there should be no release for the fermenter while there is a need of the o-ring or a seal. So when there is a material mean glass to glass or glass and metal or metal to metal because the joint in case of a small scale when we talk about the glass vessel and there the top plate should be the stainless steel. So when we talk about the joint between the two solid object so it is not possible to have a very close contact and between two solid surface because the microorganisms from where the air can pass then the contaminants can come inside and then the microorganism has the chance to escape from that. So then we have some flexible rubber like material that can be utilized as a seal or o-ring. So that can withstand that is not only the first for the choice of the seal and the o-ring that can also have some because that can withstand some temperature effect while making the sterilization. So as concerned with the glass and the metal seal can be made with compressible gasket or lip seal or o-rings. So with metal to metal joints only the o-ring are suitable but this can only be placed in a groove. So it can only be placed on the end plate of the fermenter but as concerned the seal that should ensure the good liquor and the gas tight joint there should be no leakage either in case of the expanding and the contracting at different rates when we have the process of sterilization and other cycle of the incubation during the fermentation process. Mostly when we talk about the type of the material used for the seal and the o-rings nitrile or butyl rubbers are normally used because the nitrile and the butyl rubbers can withstand and can give us that quality which we need in a fermentation process. So mostly the nitrile and the butyl rubbers are used in fermenter design. So you can see in this slide that three different kind of the joints and the symbolic representation in first case you can see that how it is a gasket type but in B case this is known as the lip type seal and in this case there is an o-ring that is only possible when we use as round shaped but there should be a groove in the top plate as that. So these are the three different type of the seal or the o-rings but in restriction when we talk about the seal and there is a difference between the o-ring and the seal but when we talk about stick sense that seal is mostly when we say about that seal which have fixed with the agitator shaft. In this case we can see here very simple seal having a single in this you can see that this is a packing material and three-dimensional shape of that and this is also three-dimensional and actually actual diagram of a seal. So such seal is mostly fixed where the agitator shaft has to has a link with the fermenter vessel. This seal is a very double mechanical seal that is mostly used in industrial scale fermenters that is reported by you can see that that mostly used in New Brunswick scientific headfield England model. So as concerned the seal sometime when we talk about the laboratory scale fermenter and when we use the glass as a construction material on a laboratory scale then there is a choice that we can avoid such seals because in a prolonged run and a prolonged for a long term use of the fermenter then there is a risk of contamination and the leakage from that. So such kind of the fermenter having no seal that is fabricated by a company new brand bioengineering company they design a small scale fermenter having the impellers and their motor and the impellers are moved with the magnetic contact. So under the magnetic the impeller having the agitation in the fermentation medium. So there is no direct contact as you can see in this there is no direct contact between the vessel and the seal. So this point is basically having the magnet and the internal that is having the magnetic effect. So that is why that used for the agitation system without the main seal. So that is why it is good only on a laboratory scale.