Round, square, or egg-shaped – sealing cushions calculations.

Not all pipes are the same. And they come in a range of shapes and sizes. Some reasons are historical, (they used brick!) some are practical.

It’s 100% important that you take the time to get all calculations right. Lives depend on it.

And remember: for non-circular special profiles, only the devices with special sealing can be used (sealing pads./cushions).

Here’re some handy rules of thumb.

ROUND PIPES:

MEASURE THE DIAMETER OF THE PIPE. Carefully measure the inside of the pipe to determine its diameter. (Measure the dimension in inches.)

DETERMINE THE BACKPRESSURE: (Air or Liquid) The pressures a plug must withstand are measured in PSI (Pounds per Square Inch.) These pressures can be calculated by determining the height of the water that accumulates (head feet) from the centreline of the pipe.

DETERMINE THE PIPE’S AREA: (square inches) R x R x 3.14.

• Divide the pipes diameter by 2 to get to radius.
• Multiply the radius by the radius.
• Multiply that number by 3.14. the resulting total will be the pipes total square inches.

EXAMPLE

Step (1) 60” Pipe diameter divided by 2 = 30”
Step (2) 30” x 30” = 900”
Step (3) 900” x 3.14 = 2826 total square inches

CALCULATE THE TOTAL POUNDS OF FORCE

Multiply the total PSI by the total square inches of the pipe. The resulting total will give you the total pounds force the plug must withstand.

EXAMPLE

10 ft of water = 4.33 PSI
4.33 PSI x 2826 Sq.in = 12,236.58 pounds of force

 

RECTANGULAR PIPES

 Important: the maximum linear distance from one point to the other must be within the diameter range of the sealing pad used.

Basically: Scope / 3.141592654 + 10%

(Height + width=U) x 2 / 3.141592654 + 10 % = diameter round.

The largest distance for rectangular profiles is normally the diagonal.

Calculation: a²+b²=√c²

 

EGG-SHAPED

Standard egg profiles (width / height ratio: 1 / 1.5)

Max. width x 1.4 = round (incl. 10% tolerance)

Important: the maximum distance from the pipe apex to the bottom must be within the diameter range of the duct sealing cushion used

 

Egg profile (w/h) mm	Min cushion size	Alternative
300 / 450	1- 600	1 – 800
400 / 600	1- 600	1 – 800 1-10000
500 / 750	1 – 800	1-1000 1-1400 1-1200 1- 1500
600 / 900	1 – 1000	1-1200 1-1400 1-1500 1-1600
700 / 1050	1 – 1200	1-1400 1-1500 1-1600
800 / 1200	1 – 1200	1-1400 1-1500 1-1600
900 / 1350	1 – 1400	1-1500 1-1600
1000 / 1500	1 – 1500	1-1600 1-1800 1-2200
1200 / 1800	1 – 1800	1-2200
1400 / 2100	1 – 2200	1-2800