Introduction to Grooved Pipe & Fittings

We previously have introduced different types and combinations of threaded fittings - which have been around for more than a century.

Here we're introducing another common way to join pipe; using grooved fittings. 

An attic sprinkler system using a grooved elbow with couplings. 

Use of "mechanical" couplings that could allow faster joining of pipe came to life in 1919 by Lieutenant Ernest Tribe. Just a few years later the Victory Pipe Joint Company renamed itself to Victaulic (a combination of "victory" and "hydraulic"), and grew to expand the technology worldwide. 

Today, Victaulic and other manufacturing leaders provide grooved fittings that are often used for pipes in fire sprinkler systems. It is not uncommon for both mains and branch lines to be grooved today.

What are common grooved fittings, and how do they work? Let's introduce them. 

An in-rack sprinkler with a branch line using (starting with the sprinkler) a groove x thread reducing elbow
​with a grooved coupling, a grooved piece of pipe, and a grooved tee (connection not shown).

PIPE
Let's start with the pipe. In order to give grooved fittings an opportunity to "grip" the pipe and remain in place, they need an opportunity to resist the pressure of the water that is trying to "pull away" the pipe from the fittings which join them together.

A grooved coupling about to connect two grooved-end pipes. Note the loose nut and bolt on the right-hand side, allowing the coupling to be expanded and "slip" over the pipe on the left.

In order to create a groove in the pipe, steel can either be "roll groove" or "cut groove". Roll groove pipe involves pressing an indentation into the pipe near the end of the pipe. This allows a grooved fitting to slip over the end of the pipe and fit into the groove. Roll groove pipe has the advantage of not reducing the pipe thickness, so it can have more tolerance for corrosion than thinner pipe, similar pipe with threads, or pipe with cut grooves.

Pipe which is cut groove involves cutting into the pipe rather than pressing it. This cutting removes a portion of the pipe wall, making a thinner but smooth interior pipe wall. This thinner wall makes it more susceptible to corrosion, however, for pipe systems with a minor slope, the smooth inside of the pipe does not create a ridge where water can sit and corrode the pipe.

Roll Grooved Pipe (top) and Cut Grooved Pipe (bottom). Note the ridge on the inside of the pipe wall for roll groove pipe, and the thinner pipe wall along the cut groove pipe.

A tape measure with a "go" or "no-go" measurement to determine if the groove is within manufacturer tolerances.

ELBOWS & TEES
Let's start with the basics. Elbows allow bends of 90-degrees (most common), 45-degrees, 22-1/2 degrees, and 11-1/4 degrees.

Why not every possible angle? What if I need to have a 60-degree bend because of my building?

First, it wouldn't be economical to make a fitting of every bend. Second, is that using just two 90-degree elbows back-to-back we're able to create a "swing joint" and make any angle we could want, just by changing the elevation of the pipe that's being joined.

Victaulic "FireLock" Grooved Fittings; 
90-Degree Elbow #001 (left), 45-Degree Elbow #003 (center), and Standard Tee #002 (right)

One notable specialty with the grooved elbow is a "Drain Elbow", which has the elbow except it includes a drain outlet at the bend of the elbow. This is used all the time with fire department connections which come down a wall and need to be capable of being drained (to avoid having water-charged pipe freeze and burst). This is also called a "Drain-El" or is a Victaulic #10-DR.

A wall-mounted fire department connection that is away from the riser, here showing the "Drain Elbow" with a ball drip below. The portion upstream of the check valve is intended to be dry unless the FDC is actively being used in order to avoid freezing water inside.

COUPLINGS
Nice sketches, Joe, but that's not how things look in the field!

That's because unlike threaded fittings, the actual pipe joining is by a grooved coupling. The coupling has malleable iron bumps that grip the indent of one groove (pipe/fitting) and connect it to the second groove (the other pipe/fitting). 

A grooved coupling (here a Victaulic #009N shown).

OTHER FITTINGS
There are a host of other fitting types. Grooved Reducing Tees? Yep. Less common. Less common can equate to more expensive, or at least that's what I hear from contractors familiar with all the pricing nuances.

What other grooved fittings do I often see? 

Reducing fittings, which is a concentric, single-cast piece of metal that has a large groove on one end and tapers down to a smaller groove on another end. One note of caution is using these in the vertical orientation; I've heard it is much better, more stable, and stronger to use a reducing-fitting as opposed to a reducing-coupling when in a vertical orientation. One of my clients goes so far to say to not use reducing couplings at all (where the coupling itself has two different groove sizes). I wouldn't have the expertise to gauge that myself.

A flange x groove reducer (left) and a grooved cap (right).

There are also reducing adapters, than can accept a flange connection and convert it to a reduced groove connection. 

Crosses are also available, as are caps (like the Victaulic #006 shown above on the right) which can terminate the end of a branch line. These caps even have 1-inch threaded opening options for easy auxiliary drains. 

Many manufacturers have equipment and components with grooved ends that can readily attach to pipe and fittings.

If you're looking to explore the extend of all available grooved fittings, I'd invite you to check out manufacturer's catalogs or do a simple google search for grooved sprinkler pipe fittings. The manufacturer's product data can do a whole lot of good in clarifying what's been created and listed for use in sprinkler systems.

Have tips, tricks, or things to consider about grooved fittings? Comment below.

​That's all for this week - hope you have a great rest of yours.