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Considers hydraulic problems (from surge), air-related problems (both vacuum and air-release), and mechanical problems (from slam) that can be addressed with valves. A technical presentation, but light on math and heavy on metaphorical examples that make the hard-to-see inner workings of a fluid system easy to visualize and understand.
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HOW TO USE VALVES TOPROTECT FORCE MAINS
Brian GongolDJ Gongol & Associates, Inc.
January 28, 2015
Nebraska Snowball Conference
Let's start with a beer keg
If you pump a few times, you add pressure
Pumping too much creates foamy beer
Beer is relatively incompressible
Releasing a little volume eases lots of pressure
Water in a pressurized system: Same behavior
Not zero like a solid (steel or concrete)
But close
Squirt guns and belly flops prove it
Water is not like air in a storm door cushion
But also unlike pushing on a pool cue
Energy is transmitted quickly but not instantly
Energy is conducted as a wave
Surge is like a train starting or stopping
Energy transmits through couplers
Slam is the train sliding back downhill
Blood pressure is a surge event
Everyone with a dishwasher knows surge
Driving while hauling tank of liquid
Don't jam on gas or brake
Operate smoothly
Sudden starts/stops could drop a transmission
Momentum/inertia matters
Centrifugal pump from stop to 100%
Like hitting gas pedal to floor
Shock demand is hard on transmission
Rotative speed isn't 100% instantaneously
Pipe friction
Fire hose/garden hose/flexible hose
PVC pipe
Ductile iron, copper, and other metal pipe
More friction means more surge dissipation
But also more headloss and energy use
High efficiency trade-off with surge potential
Magic number: 10 critical periods
Cross-cancellation of wave action
Surge moves at the speed of sound in water...
...modified by pipe characteristics
Published tables of surge wave speed ("a")
"a" for plastic pipe is 900 fps (615 mph)
"a" for ductile iron is 5,000 fps (3400 mph)
Plastic expands and absorbs the wave energy
Metal disspates less wave energy
Surge mitigation techniques
VFDs might help
But what part of the scaleis actually effective on surge?
Depends upon static head
Soft starters might help
But what about pump shutdown?
What about power failure?
Automatic pressure-control valves
Air is also a problem
Air release upon pipeline fill
Dynamic operation to release air
Vacuum-breaking upon pressure drop
Air in solution in water: About 2%
Air valves
Air restricts pipe diameter
Can be significant
Air pockets will build
Imagine trapping a tough balloon in the pipe
Lots of compression possible...
...but dangerous high pressure results
Weight of a column of water
4" diameter, 500' long 43.55 cubic feet 325.75 gallons
At 8.3 lbs per gallon: 2700 lbs. (a Honda Civic)
You have to break that vacuum
Pipe is not like a drinking straw
Something has to give eventually
How it's harmful
Long-term wear on pipes
Main breaks
Valve failures
Backspinning pumps
Pipe swings inside plant
Leaks
Contamination by negative-pressure events
We've covered hydraulic problems (air/water)
Upsurge and downsurge are hydraulic
Slam is mechanical
Slam comes from column reversal
Slam and surge are independent
Check valves are used for protection
Prevent simple column reversal
Ball check valves
Weighted-flapper check valves
Cushioned check valves
Non-slam check valves
Close fast enough to prevent slam
Don't close too fast for pumps and systems
Quick self-closure isn't actual slam
Slam is involuntary seating of the valve
Some valves can control both surge and slam
Checktronic Overcoming high head after bringing pump up to speed
Illustrations
Tank to closed valve
Pump to closed valve
Demo: Surge valve
Demo: Sewage air-release valve
Demo: Water air-release valve
Demo: Wide-body air-release valve
To recap
Pipes, valves, and equipment are endangered by three problems:
Hydraulic upsurge and downsurge
Hydraulic consequences of air
Mechanical slam
These problems can be resolved through multiple means Automatic valves are often the best choice
You don't have to figure it out alone
Free surge analysis available Call: 515-223-4144
Email: info@djgongol.com
Questions?
Thank you for coming!
Thank you for your attention!
Contact us anytime with questions
Brian Gongol DJ Gongol & Associates 515-223-4144 info@djgongol.com
References
Catalog photos of valves are courtesy GA Industries All other photos are original work by Brian Gongol. All rights
reserved.
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