MeyerFire
  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • About
    • Catalog
    • Content Library
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT
Picture

Best Way To Cut-In Backflow on Underground?

2/25/2020

7 Comments

 
What is the best way to cut in to an existing underground line that may have a thrust block at the end?

We are doing a project that has scope to retrofit an 8" backflow into an existing approximately 200' of 8" underground. There is an existing detector check valve in the line which will be removed. Because of the age of the building and underground (about 30 years old) it is assumed the piping has a thrust block at the end. But with cutting into the line and adding a couple 90 degree elbows to get the backflow above ground there is fear that the line may slip back to the water main because the thrust block at the end of the 200' run is no longer holding the entire line in place.

We are planning to add a thrust block to the new 90s, but the issue is that there is only a shut off valve that is in the straight line of the 200' of pipe. If we shut that valve, there will still be pressure on the front side of the valve and when we cut into the pipe, the pipe may slip.

Any suggestions on securing the pipe on the supply side of the new backflow or limiting the pressure prior to the concrete being poured on the elbows for the backflow?

​​​​​​​​Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
7 Comments
Darrell
2/25/2020 10:14:26 am

My understanding of thrust blocks is limited, but I believe they are only applying force when water is flowing. The thrust block is sized to apply a reaction force to the flowing water. If you have a shut off valve, where no water is flowing during the BFP addition, then the pipe is seeing no force.

Reply
RyanO
2/25/2020 10:15:30 am

I had a similar situation a few years ago where we just poured concrete between the two ells below grade. Everything else was assembled with Grip Ring retainer glands. It has never moved.

There are also a few manufacturers that make assemblies specifically for this. Look at Watts(Ames) website under backflow preventer accessories. They're called Valve Setters.

Reply
RyanO
2/25/2020 10:18:10 am

I may have misread the problem. Are you concerned about the valve blowing off after you cut in downstream? Only way to mitigate this is to retain the valve with a large "deadman" upstream, or isolate the supply to the valve.

Reply
Peter
2/25/2020 01:34:03 pm

The concern is the valve or pipe before the valve pulling out of the tee (or 90) after the pipe is cut out, prior to setting the new MJ 90 ell that will be the supply side of the new backflow preventer. Once the new MJ 90 is set, a new thrust block can and will be poured but it is the time period between cutting into the pipe before a temporary thrust block (with wedges or some other anchoring) can be performed.

I had thought about using an EBAA 1100SDB in a dead man like you had suggested just upstream. We've cut in a number of backflows, but the valve had always been upstream of another 90 or tee. This one is about 4' in front of where we need to cut in. We are planning to dig back to the valve and we've already spoke to the water municipality who has ownership of the valve about the potential issue. They haven't offered too much advice.

Reply
C.T. Carbonari link
2/25/2020 04:37:16 pm

I would use a restraining collar and rod back to a deadman poured just downstream of the valve. (A collar from a Bell & Spigot restraint set should work just fine and is probably what I would grab if I was on the jobsite). If I understand your conditions correctly then rodding the pipe back to a deadman should prevent any longitudinal slippage throughout the run of pipe back to the Ell (or Tee).

You propose an interesting Risk/Assessment question. I would think the probability of any joints slipping loose is very minimal (under typical line pressures, with no thrust, and the weight of the ground acting as a retaining force). With that said, the results of being wrong could be catastrophic.

A healthy fear of pressure is a good trait to have in this business and I would always err towards the side of caution and safety.

Reply
Peter
2/25/2020 08:02:48 pm

I am probably being over cautious. The existing pipe underground is steel and the connections visible are welded flanges. There may be no thrust block at all and the pipe may be welded back to the tee. However given the set of circumstances on a 30+ year old install I feel it better to be over cautious. There is an existing concrete valve pit we can use as a dead man and rod back to. This should at the very least provide enough of a restraint until the thrust blocks on the new underground elbows are cured.

Reply
C.T. Carbonari link
2/26/2020 09:08:40 am

Black Steel? Not Ductile Iron? That would give me even more concern of existing piping integrity due to increased likelyhood of corrosion.

Like you, I am overly cautious as well. I've seen deadend MJ Valves pop off. Granted, it was after ~3.5 hours of hydro @ 200 psi and we were running the jumping jack in the trench all morning during backfill (I'm convinced we were trapping air at the end of the lateral). Not one of my Boss's wiser ideas.




Leave a Reply.

    Picture
    Why Sponsor?

    ALL-ACCESS

    Picture
    GET ALL OUR TOOLS

    SUBSCRIBE

    Subscribe and learn something new each day:
    I'm Interested In:

    COMMUNITY

    Top ​June '22 Contributors
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    SEE LEADERBOARD

    YOUR POST

    SUBMIT A QUESTION

    PE EXAM

    Get 100 Days of Free Sample Questions right to you!
    SIGN ME UP!

    FILTERS

    All
    A117.1
    ABA
    ADA
    ASCE 7
    ASME A17.1
    Daily Discussion
    Design Documents
    EN 12845
    Explosion Protection & Prevention
    Fire Detection And Alarm Systems
    Fire Dynamics
    Flammable & Combustible LIquids
    FM Global
    Human Behavior
    IBC
    ICC-500
    IFC
    IMC
    IPC
    IRC
    ISO
    Means Of Egress
    NFPA 1
    NFPA 10
    NFPA 101
    NFPA 11
    NFPA 110
    NFPA 1142
    NFPA 1221
    NFPA 13
    NFPA 13D
    NFPA 13R
    NFPA 14
    NFPA 15
    NFPA 17A
    NFPA 20
    NFPA 2001
    NFPA 214
    NFPA 22
    NFPA 220
    NFPA 24
    NFPA 241
    NFPA 25
    NFPA 291
    NFPA 30
    NFPA 33
    NFPA 400
    NFPA 409
    NFPA 415
    NFPA 497
    NFPA 5000
    NFPA 502
    NFPA 54
    NFPA 55
    NFPA 654
    NFPA 68
    NFPA 70
    NFPA 72
    NFPA 75
    NFPA 90A
    NFPA 92
    NICET
    Passive Building Systems
    PE Prep Guide
    PE Prep Series
    PE Sample Problems
    Poll
    Smoke Management
    Special Hazard Systems
    UFC 3 600 01
    UFC 3-600-01
    UFC 4-021-01
    Updates
    Water Based Fire Suppression
    Weekly Exams


    ARCHIVES

    July 2022
    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    November 2016
    October 2016
    July 2016
    June 2016


    PE PREP SERIES

    Fire Protection PE Exam Prep
    SEE LEADERBOARD

    RSS Feed

Picture
​Home
Our Cause
The Blog
The Forum
PE Exam Prep
The Toolkit

MeyerFire University
​Pricing
Login
​Support
Contact Us
Picture

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

​MeyerFire, LLC is an International Code Council Preferred Education Provider.

All text, images, and media ​Copyright © 2022 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. 
The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • About
    • Catalog
    • Content Library
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT