blog about Guide to Pressure Vessel Head Design and Volume Calculation

Selecting the appropriate head type for pressure vessel design presents a critical challenge for engineers. The choice impacts not only equipment performance but also safety and cost-efficiency. This comprehensive guide examines three common head types and provides practical volume calculation formulas to streamline your design process.

Torispherical heads, also known as dished heads, offer an optimal balance between affordability and mechanical performance. Their design features a spherical cap connected to a knuckle (transition radius), which effectively distributes stress for reliable pressure containment.

• Crown Radius (R): Equal to head diameter (D)
• Knuckle Radius (r): Typically D/10
• Head Height (H): Calculated as D × 0.194 + SF + t (SF = straight flange height, t = thickness)
• Blank Diameter: D × 1.11 + 2SF for material cutting

Excluding straight flange height, volume (gallons) ≈ [D (inches)/12]³ × 0.582. This simplified formula enables rapid capacity assessment during preliminary design phases.

The 2:1 ellipsoidal head has become the industry standard for high-pressure applications due to its excellent stress distribution characteristics. Its semi-elliptical profile approaches hemispherical geometry while maintaining material efficiency.

• Crown Radius (R): 0.90D
• Knuckle Radius (r): 0.17D
• Head Height (H): D × 0.25 + SF + t
• Blank Diameter: D × 1.15 + 2SF

Volume (gallons) ≈ [D (inches)/12]³ × 0.954. Ellipsoidal heads provide approximately 64% greater capacity than torispherical designs at equal diameters.

Hemispherical heads represent the theoretically optimal pressure containment geometry, distributing stress uniformly across the surface. Their manufacturing complexity and material requirements result in significantly higher costs, limiting use to extreme pressure applications.

• Inside Radius (IDR): D/2
• Head Height (H): D/2 + t
• Blank Diameter: πD/2

Volume (gallons) ≈ [D (inches)/12]³ × 1.958. Hemispherical designs offer the largest capacity among standard head types.

Manufacturing processes, particularly forming operations, can cause material thinning—especially in transition areas. Engineers must account for this through either:

• Adding 10% margin to calculated minimum thickness, or
• Applying thickness-specific allowances: 1.5mm for heads ≤12mm thickness; the greater of 1.5mm or 15% of minimum thickness for heads >12mm

Optimal head selection requires careful evaluation of operating pressure, budget constraints, space limitations, and fabrication capabilities. Torispherical heads serve well for moderate pressure applications, ellipsoidal designs excel in high-pressure environments, while hemispherical configurations provide ultimate performance for extreme conditions. These volume calculation formulas and design parameters enable engineers to make informed decisions that balance performance, safety, and cost-effectiveness.