Fire Hose Couplings

In order for a fire hose to work safely and effectively, proper coupling selection is essential. A hose coupling is a type of fitting located on the end of the fire hose, which is typically made of steel, brass, or aluminum. The coupling has threading on each end, one female end and one male end, allowing the hose to connect with another hose, tap, or other water source. In order to attach the two threaded devices together, several factors must be considered, such as size, gender, and thread standard. To better understand fire hose couplings and threading, consult this helpful guide.

Coupling Gender
Hose couplings come in three different genders: male, female, and universal. The gender of a hose coupling is easy to determine by looking at its threads. Male coupling has threads on its outside and female coupling has threads on the inside. Universal coupling, on the other hand, can be joined to any other end of the same diameter rather than having a distinct male or female end.

Coupling size
To ensure that your fire hose functions properly, it's important to choose the correct size coupling for your application. To determine the size of the coupling that your hose will require, check the number on the female coupling. Other options for determining the correct size of the required coupling include measuring the diameter of the inside of the male coupling or looking for numbers stenciled on the fire hose.
Thread standards
Understanding the different thread standards of fire hose couplings is essential for properly matching fire hose devices together. While there are many different types of fire hose threads, there are three main types that are most commonly used in fire departments. The most common types of fire hose threading are identified by the initials NH or NST, which refer to national standard thread; NPT, which stands for national pipe threads; and NPSH, which represents national pipe straight hose thread.

To determine what type of thread standard your coupling requires, check for a stamp with the initials of the thread's standards on the female couplings of the hose you plan to replace, the water source adapter, or fitting. In the case that there isn't a stamp in any of those locations, you can determine the thread standard by measuring the male coupling's outside diameter, or circumference.

Before you start to couple fire hose you need a good understanding of what an expansion ring coupling is, the names of its parts and how it works.

The Concept Is Simple: A brass ring is expanded inside the fire hose which traps it against the coupling bowl. All critical parts are inside the coupling.

To the left is a set of standard, 1-1/2" expansion ring couplings for double jacket fire hose. The coupling with exposed threads is the male coupling. The female coupling is equipped with a swivel that has internal threads. The swivel on modern couplings is held on with a "piston ring" type snap ring that cannot be removed once it is assembled. Older couplings might have a plug on the female swivel. When a plug is present it indicates that the swivel is held on with bearings which are removed and installed through the hole the plug fills.

In the past it was possible to simply change out the swivel if it became out of round or damaged. Unfortunately modern couplings have be be completely replaced when the swivel is damaged.

The raised ridges on the body of the male and the swivel of the female are known as rocker lugs. These lugs are engaged with spanners to tighten and loosen the couplings. The notch on the lugs is called a higbee notch or higbee cut (I have also seen it spelled higby). The notch indicates exactly where the first thread starts. If you look closely you can see the thread just beginning where the notch is on the male coupling. When a firefighter is in a hurry to connect two hoses he can align the notches and be rewarded with engaged threads with less than half a turn of the swivel.

The section of the coupling the hose is attached to is called the bowl. As you can see in the picture to the left, the bowl has distinct ridges. The ridges have an almost sharp edge which slopes toward the rear of the coupling and is straight toward the front. This geometry aids in inserting the hose but locks the hose in place once the expansion ring is expanded.

The rounded opening edge is slightly smaller in diameter than the rest of the bowl portion. A correctly seated and expanded ring will wedge the hose against this smaller opening as an additional means to retain the fire hose.

There are two gaskets associated with a female coupling and one with a male coupling. A swivel (or face) gasket is inserted into the swivel of the female coupling to seal it when attached to a discharge or a male coupling. The other gasket is known as a tail (or butt) gasket. The tail gasket forms a seal between the expansion ring and the coupling. While there is a slight difference in outside diameter, the easiest way to tell the two gaskets apart is the thickness. A tail gasket is twice as thick as a swivel gasket as can be seen in this picture.

The expansion ring is the most important piece in the whole setup. It is this ring that, when expanded, holds the hose tightly to the bowl of the coupling while sealing against the tail gasket. Expansion rings are chamfered at one end to make it easier to install. Expansion rings are shown for 1", 1-1/2", 1-3/4", 2-1/2" and 3" hose. The chamfered edge is visible on the largest ring.