In the first segment of our 2-part series on irrigation design for sports fields, Donald D. Franklin of Franklin Irrigation Consulting, FIC, covered the effects of wind, head placement, and other factors on a design as a whole, in addition to providing some valuable tips for selecting and spacing heads. In this second presentation, Donald will pick up where he left off with Part 1, providing insight into everything from water velocity to pressure surges, water hammer mitigation, pipe sizing for long-term success, and analysis of different welding techniques.
Note: The following catalog of content covered in this webinar is time stamped to allow you to follow along or skip to sections of the video that are relevant to your questions. You can also search for content on this page using the FIND command in your browser (CTRL + F in Windows, Command + F in Mac OS.)
- Velocity: 5 Foot Per Second (FPS) Rule
- Pressure Surges & Water Hammer
- Fittings & Thrust Blocks
- Gasketed vs. Solvent Weld: Which Is the Best?
- Thrust Blocks
0:00 – 4:07: Intro/TOC
Review of Part 1 (1:42)
Additional information: resources from the Irrigation Association and other sources (2:49):
- Irrigation, Sixth Edition
- Principles of Irrigation
- Designing, Operating, and Maintaining Piping Systems Using PVC Fittings by Ron D. Bliesner
- Handbook of Technical Irrigation Information (Hunter Industries)
- Professional Turf Manager's Efficient Irrigation Practice (Rain Bird)
4:08 – 9:03: Velocity: 5 Foot Per Second (FPS) Rule
Velocity and pressure: review of frictional loss charts (4:08)
5 FPS second rule: Basic hydraulics teaches us that water should travel no faster than 5 feet per second to control pressure surges.
Velocity and mass (5:44)
The larger the pipe diameter, the more volume of water and weight it carries.
9:04 – 23:03: Pressure Surges & Water Hammer
Calculating pressure surges and water hammer (9:59)
Factors that create pressure surges and water hammer (10:59):
- Operating pressure
- Length of pipe
- Time it takes, in seconds, for a valve to close
Causes of pressure surges and water hammer (14:37):
- High velocities
- Large volume of water
- Change in direction
- Long pipe runs
- Air trapped in the line
- Valves switching on and off
Additional pipe information such as pressure and burst ratings:
Mitigating pressure surges and water hammer (15:57)
- Slow velocities
- Reduce demand
- Increase pipe size
- Install pressure-regulating valves
- Install pressure relief valves
- Install continuous air release valves at high points/end of mainlines
Final benefits of slowing velocities (17:36):
- Slowing the water below 5 fps mitigates pressure surges and water hammer.
- Reduces costly repairs in labor, material, etc.
- Repairs can introduce debris and air into the system, causing more damage to the system.
- Allows for a change in velocities over time.
- Incorrect nozzles installed by maintenance.
Changing velocities over time: issue (18:39)
Changing velocities over time: result (20:01)
Some causes of dry spots, or "donuts" in sports fields:
Changing velocities over time: solution (20:51)
23:04 – end: Fittings & Thrust Blocks
Gasketed vs. Solvent Weld: Which is Best? (23:04)
Gasketed vs. solvent weld: Installations (23:38)
Gasketed and mechanical fitting require:
- More labor to install
- Thrust blocks against "non-distributed" soil
Solvent weld pipe and fittings:
- Require faster installation and less labor
- Typically do not require thrust blocks
Cost difference: Mechanical fittings may cost three times more than solvent weld.
Sizing thrust blocks (source: EJP) (26:40)
Thrust blocks (48:49)
- Thrust blocks should be installed against undisturbed soil.
- Concrete placed over the top and on both sides of the fitting is not acceptable.
- Stones, bricks, concrete blocks, and wood are not proper thrust blocking material.
Review of how water hammer happens (32:31)