[copachino]

hi all, im trying to undestand why beer fermenters have a dome shapped top, i believe that its for pressure distribution for isobaric fermenter but, for non isobaric fermenters its there any use on that or its just that they look good.

the main reason its because i want to make me a 10bbl fermenter, i got all the equipment uncludinf the shop for sanitary welding (not mine but a friend of mine), so i can make it conical with out problems but the dome top its quite hard to make, im trying to make it simple, flat top with a big 12 inch ferrule on top and a 4 inch reduction ferrule for the arm and the spray ball, main use would be mead and wine.

so the main question its does a flat top could be a problem?, should be ok to add a manhole in the middel of the tank?

[kramerog]

Some of the most common fermenters for fermentations at atmospheric pressure have flat lids such as bucket fermenters. I have seen adjustable volume fermenters having flat lids too. 

[denny]

I don't see that it would be an issue

[BrewBama]

The domed lid is for pressure. Either fermenting under pressure or pressure transfers.  I don’t do either. If you do or want to you might consider a domed lid. Otherwise, it’s an unused feature.



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[denny]

The domed lid is for pressure. Either fermenting under pressure or pressure transfers.  I don’t do either. If you do or want to you might consider a domed lid. Otherwise, it’s an unused feature.



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Since I was ignorant of this, can you tell me why a domed lid is needed for pressure uses?  I had no idea.

[BrewBama]

I guess the qualifier is how much pressure. I’ve learned that very low pressure (1-2psi) can be used with my flat BrewBucket lid. …but higher than that and a domed lid is recommended.

Theoretically, a sphere would be the best shape of a pressure vessel. But a spherical shape is tough to manufacture, therefore more expensive, so most pressure vessels are cylindrical with 2:1 semi-elliptical lids (aka heads).

There are several designs of pressure vessel lids: Ellipsoidal Head, Hemispherical Head and Torispherical Head are three types of ASME Pressure Vessel Dished Heads.

Ellipsoidal head
This is also called a 2:1 elliptical head. The shape of this head is more economical, because the height of the head is just a quarter of the diameter. Its radius varies between the major and minor axis.

Hemispherical head
A sphere is the ideal shape for a head, because the pressure in the vessel is divided equally across the surface of the head. The radius (R) of the head equals the radius of the cylindrical part of the vessel.

Torispherical head
These heads have a dish with a fixed radius (CR), the size of which depends on the type of torispherical head. The transition between the cylinder and the dish is called the knuckle. The knuckle has a toroidal shape.



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[denny]

I guess the qualifier is how much pressure. I’ve learned that very low pressure (1-2psi) can be used with my flat BrewBucket lid. …but higher than that and a domed lid is recommended.

Theoretically, a sphere would be the best shape of a pressure vessel. But a spherical shape is tough to manufacture, therefore more expensive, so most pressure vessels are cylindrical with 2:1 semi-elliptical lids (aka heads).

There are several designs of pressure vessel lids?  Ellipsoidal Head, Hemispherical Head and Torispherical Head are three types of ASME Pressure Vessel Dished Heads.

Ellipsoidal head
This is also called a 2:1 elliptical head. The shape of this head is more economical, because the height of the head is just a quarter of the diameter. Its radius varies between the major and minor axis.

Hemispherical head
A sphere is the ideal shape for a head, because the pressure in the vessel is divided equally across the surface of the head. The radius (R) of the head equals the radius of the cylindrical part of the vessel.

Torispherical head
These heads have a dish with a fixed radius (CR), the size of which depends on the type of torispherical head. The transition between the cylinder and the dish is called the knuckle. The knuckle has a toroidal shape.



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Thanks for that, but I'm still left wondering why.

[hopfenundmalz]

Flat panels have little strength. Curved panels have much more strength.

[narvin]

Have you thought of building it and testing it out MythBusters style?  Make sure to film it for us.   

[BrewBama]

Because circles can withstand internal pressure by pure tension in the tank material instead of bending.

If the shape were not circular, then there would be bending stresses applied and it would not be able to withstand as much pressure without breaking.

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[denny]

DUH!  It's so obvious once someone tells you!  Thanks, gentlemen!

[Saccharomyces]

Flat panels have little strength. Curved panels have much more strength.

With a sphere offering the greatest strength because pressure is equally distributed.