Exposed FDC; Siamese Connection

Learn about Siamese fire department connection components, uses, and accessories

The fire industry has lingo for all kinds of equipment, and one term that is often used is "Siamese connection." This fire department connection (FDC) features two twin female inlets that are attached at an angle to the body (hence the term Siamese) and it plays an essential role in providing supplemental water to sprinkler and standpipe systems. Fire departments typically utilize FDCs when large fires have threatened or bypassed initial suppression efforts. The two Siamese-like couplings connect servicing hoses that pump water from fire engines.

Learned enough already? Browse QRFS’s FDC Siamese Connections here.

 Keeping Siamese connections code compliant

FDCs are one of the most important tools for firefighters at the scene of a fire, and there are several requirements in place to guarantee their accessibility. One of them has to do with the distance between a building’s fire hydrant and its Siamese connection: Any building that uses a fire suppression system should have a fire hydrant positioned no closer than 30’ to the Siamese connection but no farther than 50’. This is to ensure there are no other fire apparatus that obstruct access to the building's FDC. For an in-depth look at all FDCs, including key regulations and installation considerations, read our blog: "The Role and Components of Fire Department Connections."

The components of a Siamese connection

  • The first thing people notice about the Siamese connection is the dual female inlets, which come in several sizes. Most buildings require 2½” inlets. However, 3” connections are used in New York City and San Francisco and 4″ and 5″ “Storz” FDCs are becoming common replacements for traditional threaded FDCs due to their simple, quarter-turn connections.
  • Siamese FDCs will contain either a single or double clapper to channel the flow of water coming into the system. With a single clapper, if one hose is connected, the other side is kept shut by the pressure of the water. If two hoses are connected, the equal pressure will cause the clapper in the middle of the body to let water flow in from each side. Double clappers provide greater control. Aside from how they function, the biggest difference between single and double-clapper models is the price; double clappers use two clappers for added durability when supplying larger standpipe/sprinkler systems, and are thus more expensive. Single clappers utilize a lone clapper, which swings freely to cover any unused inlets via water pressure.
    An FDC with a single clapper.

    This FDC contains a single clapper.


  • The attached, threaded brass ring that connects fire hoses, breakable caps, and plugs is known as the swivel. The swivel features lugs on the outer ring to support breakable caps.
    An FDC with one swivel (left side) attached.

    A Siamese FDC with one swivel (left side) attached.


  • The next components are the FDC plugs or breakable caps. The inlets in Siamese connections need to be covered. Exposure can lead to the accumulation of foreign material which can clog waterways. FDC plugs, which come standard with most purchases, feature a chain for quick retrieval when removed. For more information on FDC plus, read our blog: "FDC Plugs: What They Are and How to Install One."
    Breakable caps on a siamese connection.

    Breakable plastic caps can be used to cover siamese connection inlets.


  • Siamese connections are required to have minimum signage. First responders need quick, specific system information when arriving on scene – whether it's what type of sprinkler system is involved or if an FDC-connected system reaches throughout an entire building. While FDCs are often marked with stamps, signage also takes the form of an escutcheon that surrounds the FDC body's entry into the building. Examples of common escutcheon signage include: “Standpipe & Auto-Sprinkler”, “Automatic Sprinkler”, “Test Connection”, or “Standpipe System.”

Things to consider when browsing for a Siamese connection

The number of female inlets and clappers, as well as the thread type, are the most important features to make sure are correct. To do this, check with local authorities; jurisdictions can differ in preferences. Siamese connections are exposed FDCs which means that you’ll need to purchase plugs or caps as well. These components prevent foreign material from clogging the FDC and its waterways. is proud to offer Siamese connections as well as several other variations of FDCs. At competitively low prices, we can provide you the fire department connection you need, as well as all the required components. Make the first step towards a complete fire protection program, and visit us today!

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This blog originally posted by Jason Hugo and Cameron Sharp at on January 2, 2019. If you like what you’ve read, check us out on Facebook or Twitter @QuickRsponseFS.