TMCO HYDRAULIC SERVICES – BACKFLOW PREVENTION

HOW DID TYPICAL BACKFLOW PREVENTION DEVICES PERFORM THROUGH THE CHCH EARTHQUAKES?

PRESENTED BY: MIKE BAKER

INTRODUCTION

Speaker: Mike BakerTM Consultants Ltd- EECA FUNDED- 35 staff- All services - All projects- All locations

ENCLOSURES AND DEVICES

-University of Canterbury installation.

ENCLOSURES AND DEVICES-Note seepage caused by silt or blockages

ENCLOSURES AND DEVICES

-Sturdy enclosure-Clearance under doors to allow adequate runoff

BACKFLOW DEVICE OVERVIEW

-No external damage to backflow preventers-Foundation pad, thrust blocks and enclosures performed well-Leaky devices caused by non-localised liquefaction and small stones-Most problematic devices simply required a cleanout-Few devices required new parts-Steel spools through slab helped with above slab stability

BACKFLOW DEVICE OVERVIEW-Encountered damage in cracked seats for the devices, more prevalent after earthquakes-Possible water hammer and increased pressure resulting from earthquakes damaged devices-Hairline cracks in balls causing leaks-Increase in particles and stones from mains pipework blocking devices

INSTALLATION

- High mass valve assembly support was critical to avoiding damage.

PIPING-Pipe work was the main issue with damage to backflow assemblies being secondary to this.

OTHER ISSUES-Illegal temporary unprotected connections were prevalent. Many still remain. - Backflow did occur, witnessed by foaming in broken street mains near commercial/industrial buildings. Maybe backflow from inadequate air gaps. -Frost protection, particularly for those devices unused over winter (spring, cartridge, test cock failures). -Water hammer theory.

OVERALL-Installation-wise I believe we are doing well. -Rigidity and support are key. -Keeping silt, stones and other debris out of the system is important. -Frost protection, particularly for those devices unused over winter (spring, cartridge, test cock failures). -A TA check up on existing systems would be prudent to check for illegal systems.