Flexible Fire Sprinkler Connections

Like most "little" things, the final few feet between the branch line and the sprinkler head in a fire protection system usually gets little, if any thought. But as increasing numbers of new and retrofit commercial projects are proving, these few feet can make a noticeable difference, both initially and over the life of the property. Using flexible connections in place of traditional hard-pipe armovers pays dividends that at first blush would seem out of proportion for such a relatively minor detail.

Flexible connections install quickly, have fewer points of potential failure, have an installed cost that is at least competitive with hard pipe, and are very accommodating of building, use or code reconfigurations. This article discusses the physical attributes of flexible fire sprinkler connections, and the financial/economic aspects of specifying flexible connections rather than hard-pipe armovers

Flexible Approaches

Within the realm of flexible sprinkler connections, however, there are several comparison points to consider that affect cost (initial, installed and lifetime) and performance. These include the material used, the design, and the degree of factory vs. onsite assembly required.

The most obvious feature, and an important delta, is the corrugated hose. Both the inside diameter and the material used affect friction loss, which can vary among different brands by more than 350% over a six-foot hose length. In practice, as systems are sized from the heads back to the main--regardless of whether they are hard pipe or flexible--the friction loss values can impact the size of the mains. One-inch "true" inner diameter stainless steel hose exhibits the best friction loss, producing equivalent-length values similar to that of a hard-pipe armover, as well as providing superior resistance to corrosion over time. Flexible sprinkler connection friction loss data is expressed in equivalent lengths of one-inch Schedule 40 pipe, and should be included in the hydraulic design calculations the same as a valve or fitting

Both the strength of the hose and its resistance to reverting to its original shape under pressure are greatly enhanced by the use of a braided sheath. The fact that only braided hose can pass the stringent testing that Factory Mutual requires for its certification (see UL/FM Testing Sidebar) illustrates its importance. As with the hose itself, the sheath material used also affects the performance.