Tips from the Plug Peddler
Pneumatic Plugs Essential Terminology.
Back Pressure: Back pressure is the amount of air or water that has built up behind (or in front of) a pipe plug.
Feet of Head or Head Pressure: The depth of the water from the centerline of the plug to the water’s surface.
Grade or Slope: The percentage the pipe is slanted downward to allow the affluent to flow. Example: If the pipe is on a 1 % grade that means the pipe gradually slants downward at a rate of 1 foot every 100 feet of pipe.
Pounds of Force: The amount of force being exerted on a pipe plug (back pressure). It is important to understand the pounds of force that a plug is holding back to help you understand the amount of damaged/danger that can be caused if a pipe plug fails or deflates. This also helps in developing or designing a proper blocking or bracing strategy.
Pneumatic Plugs Essential Calculations
Pounds of Force Formula:
3.14 x (radius of pipe²) = square inches or area of the pipe. Multiply this figure by PSI (back pressure) to calculate pounds of force.
Example: If a plug is installed in an 8-inch pipe and the plug is holding back 5 PSI of air pressure, how much force is the plug holding back?
- Calculate the surface area of 8”-diameter pipe: 3.14 x 4(pipe radius)² = 50.24 square inches
- Multiply the back pressure (5 PSI) x square inches: 5 x 50.24 = 251.20 pounds of force
Calculating feet of head using the slope or grade of the pipe:
To calculate the feet of head/head pressure that is backing up behind a pipe plug, you must know the grade or slope of the pipe and the distance the water is backing up behind the plug.
If a pipe is laid on a 1% grade and the water inside the pipe has backed up 500 feet behind the plug, then the plug will be holding back 5 feet of head.
Example: The number of feet the water is backed up in the pipe behind the plug equals 500 feet multiplied by the slope or grade. In this case equals 1% or .01 = (500 x .01 = 5 feet of head). Every additional 100 feet the water backs up would add one additional foot of head to the back pressure.
Pneumatic Pipe Essential Conversions
General Conversion Table
Pressure Conversion Table