Protecting force mains with valves

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: [email protected]

Questions?

Thank you for coming!

Thank you for your attention!

Contact us anytime with questions

Brian Gongol DJ Gongol & Associates 515-223-4144 [email protected]

References

Catalog photos of valves are courtesy GA Industries All other photos are original work by Brian Gongol. All rights

reserved.