Share:
How It Works
When a pipe operates under internal vacuum (e.g., during rapid drainage or pump suction), atmospheric pressure pushes inward on the pipe walls. The vacuum load per linear foot equals the vacuum pressure times the inside diameter divided by 12. This load adds to external soil and wheel pressures in the total design check.
Example Problem
A 24-inch pipe experiences 200 lb/ft² vacuum pressure. What is the vacuum load?
- WV = 200 × 24 / 12 = 400 lb/ft
Frequently Asked Questions
What causes vacuum in a buried pipe?
Rapid drainage of a full pipe, pump suction, or water column separation after a valve closure can all create internal vacuum. The pressure difference between atmosphere and the partial vacuum pushes the pipe walls inward.
How much vacuum pressure is typical?
Full atmospheric vacuum is about 2,116 lb/ft² (14.7 psi). Most buried pipe systems see partial vacuums of 100–500 lb/ft² during transient events.
How can vacuum collapse be prevented?
Air-release valves, vacuum breakers, and thicker pipe walls all help prevent collapse. Designing the system to avoid rapid flow changes is the most effective prevention method.
Related Calculators
- Pipe Hydrostatic Pressure Calculator — external water pressure on buried pipe.
- Buried Plastic Pipe Calculator — combined pressure, thrust, and wall area.
- Pipe Soil Pressure Calculator — soil weight pressure and buoyancy factor.
- Pipe Wheel Loading Calculator — wheel loads at various cover depths.
- Fluid Pressure Calculator — calculate hydrostatic pressure at any depth.
- Pressure Unit Converter — convert vacuum and pressure between different units.
National Resources Conservation Service. National Engineering Handbook. 1995. USDA.