Head (vessel)

Steel Pressure Vessel

The end caps on a cylindrically shaped Pressure vessel are commonly known as heads.

[edit] Head shapes

The shape of the heads used can vary. The most common^[1]^[2] head shapes are:

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.

Storage silo with a hemispherical head
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.
Torispherical head: These heads have a dish with a fixed radius (r1), the size of which depends on the type of torispherical head.^[3] The transition between the cylinder and the dish is called the knuckle. The knuckle has a toroidal shape. The most common types of torispherical heads are:

Schematic of a torispherical head

Klöpper head: This is a torispherical head. The dish has a radius that equals the diameter of the cylinder it is attached to ( $r 1 = D o$ ). The knuckle has a radius that equals a tenth of the diameter of the cylinder ( $r 2 = 0.1 * D o$ ), hence it's alternative designation "Decimal head".
Korbbogen head: This is a torispherical head. The radius of the dish is 80% of the diameter of the cylinder ( $r 1 = 0.8 * D o$ ). The radius of the knuckle is ( $r 2 = 0.154 * D o$ ). This shape^[4] finds its origin in architecture.^[5]

Flat head: This is a head consisting of a toroidal knuckle connecting to a flat plate. This type of head is typically used for the bottom of cookware.

Pans typically have a bottom in the shape of a flat head
Diffuser head: This type of head is often found on the bottom of aerosol spray cans. It is an inverted torispherical head.

Typical application of a diffuser head: the bottom of an aerosol spray can
Conical head: This is a cone shaped head.