Heads, ASME dished torispherical

Solids suspension is usually carried out in mechanically agitated vessels with or without draft tubes, as shown in Figs. 5 and Dished heads (ASME dished, elliptical, or torispherical heads) are preferred. A single impeller is usually sufficient for off-bottom solids suspension in vessels with dished heads and 7 < 1.3. Dual impellers are recommended for vessels with 13 < H/T < 2.5, which are used for uniform suspension of fast-settling solids. Three or more impellers... 

Figure 4-3. Various types of more common formed heads a, flanged only b, flanged and shallow dished c, flanged and standard dished d, ASME Code flanged and dished (torispherical) e, elliptical dished (ellipsoidal) f, hemispherical g, flanged and conical dished (toriconical).

The volumes of heads must be calculated separately and added to the volume of the cylindrical portion of the tank. The four types of heads most frequently used are the standard dished head, torispherical or ASME head, ellipsoidal head, and hemispherical head. Dimensions and volumes for all four of these types are given in Luken.s Spun Heads, Lnkens Inc., Coatesville, Pennsylvania. Approximate volumes can also be calculated by the formulas in Table 10-65. Consistent units must be used in these formulas. 

Thin-walled vessel theory predicts that the thickness required for torispherical heads (depending on the dish radius) is usually greater than the shell thickness if the same allowable stresses and joint-efficiencies are used. The 1962 ASME Code Section VIII, Division 2 gives the following equation for thin-waUed torispherical dished heads in which the knuckle radius is 6% of the inside crown radius, ... 

If the hemispherical dished head is not feasible, the ellipsoidal dished should be preferred over the torispherical dished head for tall vertical vessels, since the cost of the top closure is only a small part of the total cost of the vessel. For a battery of horizontal storage tanks or small vertical vessels, the torispherical dished head may be the more economical choice. Closures with conical, tori-conical, flanged and dished (not ASME) or flat shapes have no place in the design of tall vertical towers unless the process requires such special shapes for some particular reason. 

A 102 inch OD F D (flanged and dished, or torispherical) head made to ASME specifications (KR > 0.60/ and KR > Sijj, where = head thickness) is spun from a 1-inch plate. The head is in the horizontal position. The liquid level is 35 inches inside the head. Determine the volume of the liquid that occupies the partial volume of the head. 

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