The pioneering inspiration behind the original concept of a metal hose – providing flexible, leak-tight, reliable, corrosion-resistant conveyance of fluid – is as relevant today as it was over one hundred years ago, particularly when considering the life safety and property protection aspects that modern fire sprinkler systems are expected to provide.  

Beginning in the 1980s, the first flexible sprinkler hoses were introduced in Japan. Arising from a need to accommodate seismic movement and absorb the damaging stresses at joints and other components in the system induced by large and rapid displacements, flexible hoses were used to connect fire sprinklers to their supply lines in lieu of traditional threaded steel pipe.  

Since then, the inherent mechanical benefits, together with ease and speed of installation, have driven a significant surge in the popularity and use of these products during the early 2000’s. The result is the adoption, specification and installation of flexible sprinkler hoses in fire sprinkler systems in almost every region of the world.  


ANCHORED ATTACHMENTS

Foundations settle and ceilings can shift and sag over time – this presents a problem to the threaded hard pipe arm-over, specifically with respect to the sprinkler position in relation to the ceiling surface. By code, hard piping is required to be anchored to the building structure separate from the ceiling structure.   
Because of this de-coupling between the pipe and ceiling, the sprinkler elevation relative to the finished ceiling surface cannot always be guaranteed to remain constant. Under an extreme “sagging” condition of the ceiling surface, a sprinkler can become excessively recessed above the ceiling surface over time, potentially to an installed condition considered to be outside its agency Listing or Approval.  
 

The issue of foundations settling and ceilings shifting or sagging presents a problem to the threaded hard pipe arm-over, specifically with respect to the sprinkler position in relation to the ceiling surface

What this really means is that in the event of a fire, the sprinkler’s operational response time and spray pattern characteristics would be severely impacted, thereby allowing the fire to grow unchecked in the affected area. 

In contrast, a flexible sprinkler hose is required (by code, its listings and installation instructions) to be securely attached with an anchoring bracket to the ceiling’s structural elements, such as suspended “T-grid” ceiling channels or wood/metal joists or studs. 

This positive bracket attachment to the ceiling structure ensures the elevation of the sprinkler in relation to the ceiling surface remains consistent over time. The inherent “adjustability” of the flexible hose accommodates the expansion, contraction, and settlement of the ceiling structure, preserving the designed operational response and water distribution characteristics of the sprinkler. 

HOSE TYPE

Flexible sprinkler hoses currently available on the market today have vastly different design constructions to their predecessors. Most are manufactured from an austenitic grade of stainless steel, however some designs are “braided” hoses, while others are “non-braided” (corrugated).  Additionally, subsets of each of these may have “wide pitch” or “narrow pitch” convolutions – again, each having some very important trade-offs affecting key performance characteristics of a hose, including minimum bend radius, flexibility and pressure resistance.

Braided sprinkler hoses are designed with an external stainless steel wire woven sleeve providing the necessary strength to withstand internal forces from system pressures, while the corrugated tubing underneath is able to remain relatively unaffected and flexible.  

Non-braided hoses, in contrast, rely on tube wall alone to provide both strength and flexibility. The non-braided hose’s convolutions are farther apart (“wide pitch”), thereby reducing flexibility and increasing stiffness. Because this type must simultaneously maintain pressure resistance while attempting to provide flexibility, albeit significantly diminished, the non-braided type falls short of fully reconciling these two critical features.  
Comparatively, braided hoses can withstand higher pressures than non-braided hoses without permanent elongation or deformation.  Braided hoses typically are also capable of achieving a smaller bend radius, permitting a greater number of bends, resulting in the ability to accommodate installations in tighter, lower clearance locations.  

A flexible sprinkler hose is securely attached with an anchoring bracket to the ceiling’s structural elements

The external braiding also provides vibration attenuation properties in a high flow condition and an added level of external abrasion protection. However, the convolution (or wave) profile, geometry, and number of convolutions per unit length, regardless of whether an external braid sleeve is present or not, have the greatest influence on flexibility. 

“Wide pitch” hose, either braided or non-braided, is more difficult to bend due to its inherently stiff cross-section and is more susceptible to “kinking” upon installation. “Kinking”, defined as a reduction in cross-sectional area due to inducing a bend beyond its limits, can occur during installation, which results in a deleterious effect on hydraulic friction-loss and corrosion resistance. 

While non-braided hose types continue to be used and are accepted in many jurisdictions, the clear answer is that “narrow pitch” braided hose types provide a higher level of performance and reliability.

Because of their superior flexibility, higher pressure ratings, vibration attenuation properties and safer net-installed-condition, these “narrow pitch” braided hose types have quickly become the standard within the fire sprinkler industry. 

CONCLUSIONS

Flexible sprinkler hoses not only install faster than hard-pipe, but more importantly they are able to accommodate ceiling shifts and sagging over time, ensuring sprinklers remain at their original installed elevation, in addition to providing superior performance over hard-piping in a seismic event. As building owners, insurance underwriters, regulatory agencies and authorities-having-jurisdiction all require an increasingly high level of performance, safety and reliability of a fire sprinkler system throughout its life, these products have become an easy choice in meeting all of these requirements.