Considerations with Flexible Sprinkler Drops

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.

Flexible Drops have limitations on minimum bend radius, the maximum number of bends allowed, and bending near the mounting nut

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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