Nozzle on a Spherical Head flat pattern

What it is

The upright cylindrical nozzle on a spherical head, its axis parallel to the head's and offset by v. Its pattern is exact: the nozzle is a cylinder, and cylinders develop.

Where it is used

Off-centre manways, instrument take-offs, vents, agitator nozzles, any plumb nozzle on a formed head.

Measurements the calculation needs

• D2 Diameter 2
• H Height
• D Diameter
• V Outlet offset
• C Branch length
• DV Divisions
• THK Thickness

Worked example

The values the form comes pre-filled with, run through the tool itself:

Diameter 2	2000 mm
Height	500 mm
Diameter	300 mm
Outlet offset	600 mm
Branch length	200 mm
Divisions	16
Thickness	8 mm
The flat pattern fits a plate of	917 × 534 mm

Frequently asked questions

Does this part give the hole in the head too?

It does not, and that is not an omission: a sphere is NOT developable. The head is formed, and what stretches in forming is on no flat drawing — marking the hole from a drawing of the head would mean marking on a surface we cannot say where it ended up. Mark the hole on the already formed head, with a thin-sheet template taken from this nozzle's mouth, or from the nozzle itself resting on it.

Where do I measure c from?

From the POLE of the head, its highest point, not from the centre of the sphere. The centre is the datum consistent with the rest of the catalogue, but here it would be a point in mid air inside the vessel that nobody can reach. The pole is where you rest a straightedge — and with it the only length guard is c greater than zero.

Is d2 the head's diameter or the sphere's?

The SPHERE's — twice the head's radius of curvature. It is not the diameter of the cap's mouth, which on a shallow head is considerably smaller. The drawing carries the whole sphere in broken line precisely so the two are not confused.

Does it work for a torispherical head?

It works on the spherical part, the central crown: enter the radius of curvature of that crown. If the nozzle falls on the knuckle radius — the toroidal band near the rim — the surface there is not spherical and this pattern does not apply.

Can I put the nozzle at the centre of the head?

You can — enter zero offset. The cut is then a flat circle and the pattern comes out a rectangle, which is what it should be.