Two weeks ago we covered Benefits and drawbacks of flexible sprinkler drops, and last week we covered Considerations with flexible sprinkler drops. This week we offer a summary of industry leaders in the U.S. market with flexible drop technology. Know someone we're missing? Contact us so we can be sure to provide a thorough summary.

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Last week we covered Benefits and Drawbacks of Flexible Sprinkler Drops, and this week's post covers things to consider when using the technology.

Maximum Bends

• The listing for each product limits the maximum number of bends that the installation can use
• The greater number of bends allowed will help allow for flexibility in the actual installation (to avoid obstructions), but the greater number of bends used also significantly impacts friction loss within the drop.
• It's important to also verify the actual number of bends used in installation so that the install does not violate the manufacturer's listing.

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Maximum K-Factors

• There are limits to sprinkler k-factors provided with flexible drops. These limitations are listed in the product data for each drop.​

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Minimum Bend Radius

• In order to prevent kinking, the UL Listing and/or FM Approval process dictates a minimum bend radius. This is listed in the manufacturer's product data.
• It's important to also verify minimum bend radius for field inspections so that the install does not violate the manufacturer's listing.

Bending Near Mounting Nut

• Some manufacturers require a minimum distance before a bend is allowed at the nut near the mounting bracket. This distance varies across manufacturers (we'll explore more next week) and is available in the product data.
• Some manufacturer's combat this limitation by providing a 90 degree elbow immediately at the reducing fitting near the mounting bracket, which offers flexibility in the hose direction directly above the sprinkler.

Hanging

• Flexible sprinkler hose fittings exceeding 6 feet in length are required to use a hanger attached to structure (NFPA 13 2016 Section 9.2.1.3.3.3, which was added in the 2016 edition)

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Pressure Loss

• We'll see this in more detail next week, but pressure loss within the flexible hoses have significant hydraulic impact, and vary widely across different products. 
• Pressure loss needs to be incorporated in the hydraulic calculations.

Types
Braided

• Braided hose is defined by the external braiding which wraps and protects the interior corrugated hose.
• This arrangement better retains internal water pressure and prevents deformation of the hose, prevents overbending of the flexible hose, and ends up being more flexible (workable) than non-braided hose
• Braided type is required by FM 1637 Standard. This approval process requires 50,000 cycle tests (under ISO 10380)

Non-Braided

• Corrugated hose only
• Can be prone to extension (corrugations can pop-out)
• Can be prone to kinking
• Can be very stiff (only tested to 100 cycles under UL test)

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• Next week I'll briefly dive into the currently available products developed by leaders in the U.S. marketplace.

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While not a code requirement, flexible sprinkler drops have quickly become a major innovation for the fire sprinkler industry. This week's post explores logistical advantages and drawbacks of the technology.

​Components

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​What is your experience?
Join the conversation and discuss what you see as advantages or disadvantages of flexible sprinkler assemblies for this post at www.meyerfire.com.

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Next week I'll explore points to consider with flexible sprinkler drops in design and inspection that I've come across in my research.

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Pipe slope is a critical element in reducing water collection following a sprinkler system drain. Water removal is important in that the largest detriment to sprinkler system life, corrosion, occurs across interfaces between air and water. Here is a quick summary of the minimum pipe slope requirements for fire sprinkler systems.

Components of a Return Bend
A return bend is the piping arrangement for pendent sprinklers where piping stems from the top of the branch pipe (riser nipple), runs horizontally (arm over), and then down to the sprinkler (drop).

Where Required
Raw Water Sources, Mill Ponds, Open-Top Reservoirs

• Required to avoid sediment and mineral deposit accumulation (NFPA 13 2002 Edition Section 8.14.18.1, 2007/2010 8.15.18.1, 2013/2016 8.15.19.1)

Dry Systems

• Although in theory return bends would trap air and prevent water from traveling to a pendent sprinkler, in practice many installers have found water trapped at pendent sprinklers in dry systems even when on return bends. This is in part why return bends on dry systems as well as sprinklers are required to be located in heated areas. (NFPA 13 2002 7.4.1.4, 2007/2010/2013/2016 7.3.2.5)

Where Not Required
Deluge Systems

• Deluge systems already provide an open orifice, so sediment accumulation to the extent that the system would be plugged is typically not a concern. (NFPA 13 2002 8.14.18.3, 2007/2010 8.15.18.3, 2013/2016 8.15.19.3)

Where Dry Pendent Sprinklers Are Used

• Sediment accumulation may be less of an issue at the sprinkler, but could still be a concern at the edge of the dry shaft. (NFPA 13 2002 8.14.18.4, 2007/2010 8.15.18.4, 2013/2016 8.15.19.4)

Wet Pipe Where K-Factors are 11.2 or greater

• In theory large orifices would be more difficult for accumulation of sediment to block. (NFPA 13 2013/2016 8.15.19.5)

So Why Use Return Bends?
1. Sediment Accumulation

• Prevent mineral deposit, pipe scale, and sediment accumulation (NFPA 13 2002 8.14.18.2, 2007/2010 8.15.18.2, 2013/2016 8.15.19.2)

2. Sprinkler Installation Flexibility

• By piping from the top of the branch pipe instead of the side, sprinklers have the flexibility to be located at the center of tile or a specific location with greater tolerance for the sprinkler installer

3. Remodel and Shell Friendly

• Where shell spaces are provided with upright sprinklers, return bends can typically be installed without modifying the branch piping
• When systems undergo remodels, taping the top of the branch piping allows for flexibility in future sprinkler placement.

Things to Consider
Hangers

• Hangers are required to prevent upward movement on the arm over piping when:
  • the arm over is steel, exceeds 12 inches, and system pressure exceeds 100 psi (NFPA 13 2002/2007/2010/2013/2016 9.2.3.5.2)
  • the arm over is steel and exceeds 24 inches (NFPA 13 2002/2007/2010/2013/2016 9.2.3.5)

Minimum Outlet Dimension

• New systems require outlets to be minimum 1-inch, but can have temporary bushings serving upright sprinklers (NFPA 13 2002 8.14.19.1, 2007/2010 8.15.19.1, 2013/2016 8.15.20.1)

Minimum Riser Dimension on Existing Systems

• For hydraulically designed systems, nipples less than 1 inch are allowed but cannot exceed 4 inches in length, and must be incorporated in hydraulic calculations (NFPA 13 2002 8.14.19.4, 2007/2010 8.15.19.5, 2013/2016 8.15.20.5)
• For pipe schedule systems, nipples less than 1 inch are allowed but also cannot exceed 4 inches in length (NFPA 13 2002 8.14.19.3, 2007/2010 8.15.19.4, 2013/2016 8.15.20.4)

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Further Reading
Minnesota Public safety Issue | Link
NFPA 13 | Link

I'd like to open the blog today with a different flavor of technical information alongside visuals which I hope you enjoy. Early in my career I realized that the value an engineer has is in the knowledge he or she gains and can then convey in order to help others.

Traditional thinking is that experience is the only way to gain knowledge and build value. While that may be true in large part, those who wish to learn without compromise naturally have more to gain and more to offer others. In this blog I hope to note takeaways I've gathered and topics which I hope to explore in more detail as part of my effort to be a relentless learner. It is my way of cementing details I've explored while garnering feedback and learning from knowledge of others.

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