Calculating System requirements

1
Calculating System requirements

• Area Ag Mechanics
• Unit Plumbing
• Lesson 3

2
What is the recommended safety limit for the
velocity of water in pipe?

• The recommended velocity limit for pipe is 5 feet
  per second.
• Has less of a chance of causing damaging surge
  pressures
• Helps reduce friction loss

3
Why is sizing pipe important in developing an
irrigation system?

• It helps to control and maintain
• PSI
• GPM

4
What are the procedures for sizing pipe using the
5 fps method?

• Step 1 Determine the type of pipe needed
• Step 2 Determine the gpm needed by the sprinkler
  head
• Start with the last head on the circuit
• Use the smallest pipe that can deliver the
  required gpm under the 5 fps velocity.

5
Sizing procedures cont

• Step 3 The next section of pipe must supply 2
  sprinkler heads
• Add the required gpm for the two sprinkler heads
• As in step 2 find the smallest pipe that falls
  under the 5 fps
• Step 4 Continue the process until you reach the
  circuit valve

6
What are the rules for sizing valves?

• Rule 1 Static pressure loss should not be
  greater than 10 from the mainline
• Rule 2 The valve should be the same size as the
  largest pipe in the lateral or no less than 1
  size smaller.
• Rule 3 The valve should not be larger than the
  largest pipe in the lateral.

7
How is the total system pressure requirement
determined?

• Determine the pressure needed to operate the
  system at the flow demanded
• Subtract it from the static pressure available
• Formula
• Pr Ps - (Po Pls)

8
Total system pressure requirement cont

• Where
• Ps Static Pressure
• Po Operating pressure for worst case head
  (Head furthest from the source in the system)
• Pls Pressure loss throughout mainline and
  worst case lateral circuit
• Pr Pressure remaining after satisfying the
  total system requirements

9
Total system pressure requirement cont

• If the result is a very low or negative number
• Designer knows the system needs more pressure
  than the system has available
• The design needs to be re-worked before
  installation begins!!