Calculate the Flow in a Pipe Full of Liquid

• 1
  Water flows through PVC pipes very efficiently.water pipes image by Byron Moore from Fotolia.com
  
  Define the liquid full-flow pipe application parameters. In this example, two 250-feet-long Schedule 40 PVC plastic pipes are taking 15-psi (pounds-per-square-inch) well water flows to two different locations at the same elevation. The first pipe is a 1-inch Schedule 40 PVC pipe, and the other is a 2-inch Schedule 40 PVC pipe. With this information, you can calculate the flows in the two pipes.
  
  
• 2). Calculate the pressure drop per 100 feet of pipe in either case. Because there is a 15-psi drop in both of the pipes across 250 feet of pipe, there would only be a 15 psi divided by 250 feet/100 feet = 6 psi for each 100 feet for both pipes.
  
  
• 3). Look up flow-pressure drop data for Schedule 40 PVC plastic pipe in the industry data chart using the link in References. The 1-inch pipe shows a flow of 20 gallons per minute, or gpm, for a 9.4-psi pressure loss, and the 2-inch pipe shows a flow of 100 gpm for a 6.5-psi pressure loss.
  
  
• 4
  PVC pipe makes it easy to fabricate reliable flow-conduit systems.pvc image by Greg Pickens from Fotolia.com
  
  Correct the two flows for the actual drops in the example. Because flow varies as the square root of pressure differential change, the flow for the 1-inch pipe is: (6 psi/9.4 psi)^0.5 = (0.63829)^0.5 = 0.7989, which when multiplied by 20 gpm yields a flow of 15.98-gpm. Similarly, for the 2-inch pipe there is a flow of 100 gpm with a 6.5-psi drop, so (6/6.5)^0.5 = 0.9607 x 100 gpm = 96.08 gpm.
  
  

Water Flow in Schedule 40 Steel Pipe

• 1
  Schedule 40 steel pipe is usually smooth-welded.Pipes image by Sergei M. Kharitonov from Fotolia.com
  
  Define the flow application. This application uses Schedule 40 steel pipe in place of the PVC pipe in the Section 1. The steel pipe has the same basic inner diameter dimensions of 1.05 inches and 2.07 inches.
  
  
• 2). Look up the flow pressure loss data for the 1-inch and 2-inch Schedule 40 steel pipes. The 1-inch chart shows a flow of 9.5 gpm with a drop of 6 psi per 100 feet. The 2-inch pipe chart indicates a flow of 63 gpm with a 7.3-psi drop.
  
  
• 3). Calculate the two flows for the two steel pipes. The industry data chart already indicates a 9.5-gpm flow for the 6-psi drop per 100 feet of 1-inch pipe, so this is your answer and no further calculation is necessary. Because the flow data for the 2-inch pipe indicates a 7.3 psi of drop for a 63-gpm flow, its calculation works out to 63 gpm X (6 psi/7.3 psi)^0.5 = 57.12 gpm.