Fire Protection Guide

Fire Department Connection Guide: Siamese Inlets & Couplings

In short: a fire department connection (FDC) is the inlet where responding engines pump water into a building's standpipe or sprinkler system. The siamese version has two inlets feeding one outlet so two engines can supply the same riser, and its inlets must match the hose couplings the local fire service carries. This guide covers the SQD100-1.6 siamese connection, the coupling options around it, and what to check before ordering.

SQD100-1.6 Fire Pump Adapter (Siamese)

2 x DN65 inlets, DN100 flanged outlet, 1.6 MPa

2.5" Storz Coupling (German Standard)

DN50-DN150, 1.6 MPa, self-sealing aluminium

HS Coupling Adapter

DN50/DN65, GB12514, anodized aluminium

Indoor Fire Hydrant Head (SN65)

DN65 indoor hydrant head for standpipe outlets

1. What Is a Fire Department Connection?

A fire department connection is the building-side interface for the fire service. When the building's own water supply is not enough — or when the sprinkler system has been isolated — arriving engines connect their hoses to the FDC and pump water into the standpipe riser or sprinkler main. The connection is therefore a pressure entry point into the building, not a water source.

Because it is used under emergency conditions, an FDC is judged by three practical questions: can the fire service connect to it quickly with the couplings they carry, can enough water be delivered through it, and is it accessible when the building is full of smoke and apparatus. Everything in this guide follows from those three questions.

A siamese connection answers the flow question with two inlets. One engine can supply the system alone if necessary; when a second engine arrives, both inlets are used and the flow into the riser is roughly doubled without either pump running at a disadvantageous point on its curve.

2. Twin Inlets, One Outlet

The SQD100-1.6 fire pump adapter is a compact siamese body: two DN65 (2.5") inlets with caps on one side, and a single DN100 (4") flanged outlet on the other that bolts to the building main. Working pressure is 1.6 MPa and the body is only 120 mm long, which matters in pump rooms and below-grade vaults where space is tight.

Two design details are worth calling out for procurement. First, the body carries an integrated control valve operated by a handwheel, so flow through the connection can be regulated rather than simply blocked or opened. Second, the inlet caps are held by braided steel safety cables — a small feature that prevents the most common scene at a real incident, where caps are set down during pumping and lost.

Construction is ductile iron / cast iron with a corrosion-resistant powder coated red finish, with a brass or stainless steel handwheel stem. The combined twin-inlet, single-outlet layout is what distinguishes a siamese from a single-inlet connection that would limit the system to one pumper.

3. Inlet Coupling Standards and Adapters

This is the specification point that decides whether an FDC is usable on the day. Hose couplings are regional: a connection that matches one fire brigade's equipment may be useless to another's. The SQD100-1.6 is supplied with 2 × DN65 inlets and caps in SQS65 / KWS65 form, and the coupling type should be confirmed against the local fire service before the order is placed.

Where a project uses German standard connections, the 2.5" aluminium Storz coupling covers DN50 to DN150 with a self-sealing edge and the Storz quick-connect geometry, in aluminium with brass or chrome-plated options and a 1.6 MPa rating — suitable for clear water and foam mixture.

For thread-to-coupling transitions on site, the HS series coupling adapter (DN50 / DN65, 1.6 MPa / 232 PSI) uses anodized aluminium alloy with standard internal and external threads to GB12514 or factory standard, so hoses and hydrant or FDC outlets can be matched without leakage. Where connection systems are specified by project standard, our CE & EN 12845 compliance guide explains how Storz, KWS and threaded systems are treated in European specifications.

4. Where FDCs Are Installed

An FDC is mounted on the outside face of the building it protects, at a point the fire service can reach with hoses from the street or hard-standing — clear of door swings, landscaping, signposts and anything that could later become a parking space. It is normally combined with a sign identifying the system it serves, so a crew arriving at a large site knows which riser they are pressurising.

On the building side it feeds the riser network: the standpipe system serving landing valves and indoor hydrant heads, and/or the sprinkler main. That is why the FDC belongs in the specification conversation alongside the building's hydrant and riser equipment rather than as a standalone purchase.

Two installation habits prevent most failures. Keep the outlet flange and body drainable so water cannot stand in the connection in freezing weather, and make sure the connection is never obstructed — an FDC hidden behind a parked delivery van is functionally absent, and it is the most common defect found on site visits.

5. Siamese Body, Storz Coupling or Adapter?

The three items solve different problems: the siamese body is the FDC itself, the Storz coupling is the connection system where a project specifies German standard, and the adapter is the field fix that lets mismatched threads and couplings still work together. A well-specified project usually needs the body and one coupling system — adapters should be the exception, not the plan.

6. Specification and Installation Checklist

• Confirm the coupling with the fire service — match the inlet type to the couplings local engines actually carry (SQS65 / KWS65 as supplied, or Storz where the project specifies it) before the order is placed.
• Check the flow path — 2 × DN65 inlets into a DN100 flanged outlet at 1.6 MPa working pressure; confirm the outlet flange matches the riser connection on the shop drawings.
• Decide on valve and cap details — the SQD100-1.6 includes an integrated handwheel control valve and capped inlets with braided steel safety cables.
• Plan the location — outside face, reachable by hose from the street, signed, visible, and protected from future parking or landscaping; specify a body that drains so water cannot stand in freezing weather.
• Specify the finish and material — powder coated red ductile iron / cast iron body, brass or stainless handwheel stem, compact 120 mm body length for confined installations.
• Request the documentation — batch pressure test reports and material certificates for the assembly, and run our B2B valve sourcing checklist before committing to a supplier. For the supply side of the same project see how to choose a fire hydrant.

Frequently Asked Questions