Fire Protection and Mechanical Equipment

FM Approved Sprinkler Hose: FM 1637 Approval and Selection Criteria

Learn what FM approval means, which tests flexible sprinkler hoses pass under the FM 1637 standard and what to check when choosing an approved hose.

ORFA Technical TeamUpdated: Oct 30, 20264 min read

FM approved stainless steel braided flexible sprinkler hose

In buildings with suspended ceilings, flexible sprinkler hoses are the most practical way to connect sprinkler heads to the branch line. Like every component in a fire protection system, however, these hoses must be tested and approved by an independent body. An FM approved sprinkler hose is a hose that has been tested to the FM Approvals examination standard for flexible sprinkler hose and appears in the approval listing.

This article explains what FM approval means, which tests are carried out under FM 1637 and what to look for when choosing an FM approved hose.

What Is FM Approval?

FM Approvals is an independent testing and certification organisation within the insurer FM Global. It tests fire protection products to its own examination standards, audits the manufacturing site and publishes approved products in its Approval Guide. FM approval is frequently required by insurance specifications and on international projects.

The key point is that an approval applies to a specific model, size, length and set of installation conditions. A product can only be regarded as FM approved when it is used within the limits defined in its listing.

What Does FM 1637 Cover?

Flexible sprinkler hoses are assessed to FM Approvals examination standard Class 1637. It covers flexible hoses with threaded end fittings that connect sprinklers in suspended ceilings, clean rooms and ducts to the sprinkler piping.

Criterion	FM 1637 requirement
Nominal size	3/4″, 1″, 1-1/4″ or 1-1/2″ (minimum inside diameter 19.05 mm)
Construction	Stainless steel inner bellows with stainless steel braided outer jacket
Minimum rated working pressure	175 psi (about 12 bar)
Maximum length	1.8 m (6 ft) including end fittings
Hydrostatic strength	Four times rated pressure, at least 700 psi

Main Tests

Fatigue test: 50,000 flex cycles under pressure.
Pressure cycling: 20,000 pressure cycles.
Vibration and vacuum tests.
Seal integrity: At -40 °C and +135 °C.
Friction loss: The hose pressure loss is determined as an equivalent length of 1″ Schedule 40 steel pipe.
Elongation: The hose must not stretch beyond the specified limit under pressure.

Why Choose an FM Approved Hose?

Verified performance: The hose has passed fatigue and vibration tests that represent seismic and ceiling movements.
Project and insurance compliance: It makes it easier to meet specifications that call for FM approved materials.
Data for hydraulic design: The equivalent pipe length established during approval lets the designer account correctly for the hose pressure loss.
Easy installation: Less pipe cutting and threading; the sprinkler position is easily adjusted to the ceiling grid.

The FM Approved Set Supplied by ORFA

The Ayvaz FM approved sprinkler hose and connection set has the following features:

Hose: AISI 316L stainless steel
Braid: AISI 304 stainless steel
Fittings: Carbon steel or stainless steel
Connection: 1″ nipple on the pipework side, 1/2″ female sprinkler adapter on the sprinkler side
Hose size: DN25 (1″)
Working pressure: up to 16 bar
Minimum bend radius: 200 mm

Tip: FM approval applies together with the length, number of bends and ceiling fixing components stated in the listing. Bending the hose more tightly or using a different fixing instead of the approved ceiling bracket may void the approval conditions.

Applications

Hotels, offices, business and shopping centres with suspended ceilings
Hospitals, schools, libraries, cinemas and theatres
Clean rooms
Buildings in seismic zones

Frequently Asked Questions

What is the maximum length of an FM approved sprinkler hose?

FM 1637 allows a maximum length of 1.8 m (6 ft) including end fittings. The usable length and number of bends are also stated in the product’s approval listing.

Is FM approval the same as a UL listing?

No. FM approval is granted by FM Approvals to FM 1637, while a UL listing is granted by UL to UL 2443. Some hoses carry both; the project specification states which one is required.

How is a flexible hose included in hydraulic calculations?

The hose pressure loss is added to the hydraulic calculation as the equivalent length of 1″ Schedule 40 pipe established during approval. This value depends on hose length and number of bends.

Conclusion

An FM approved sprinkler hose combines the installation convenience of a flexible connection with independently verified performance. When the length, bending and fixing conditions in the listing are respected, it provides a reliable sprinkler connection. Explore all options in our Sprinkler Hoses and Connection Sets product group.

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