How to Inspect for K-Factors and Orifices?

MeyerFire University | FX103.17

By Franck Orset

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• Notes Page

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TRANSCRIPT

How do you inspect for K-factor and Orifices? 

ORIFICE CHECK

We’re continuing on our series of inspections from the perspective of an insurer, here, covering how we inspect for correct k-factor and sprinkler orifices. 

What is an orifice, and what is a k-factor? 

We cover this in more detail elsewhere, but in short an orifice is the size of the opening that allows water to travel from a pipe out to the sprinkler deflector. 

The orifice varies in size, but has a major impact on the sprinkler's k-factor which ultimately governs the sprinkler's relationship between flow and pressure. Opening sizes vary fairly dramatically but in general are not a major driver for sprinkler selection. 

Here are common orifice sizes, depending upon the k-factor of the sprinkler. These correlations are defined in NFPA 13:

k2.8 matches a 3/8" orifice 
k4.2 matches a 7/16" orifice 
k5.6 matches a 1/2" orifice 
k8.0 matches a 17/32" orifice 
k11.2 matches a 5/8" orifice 
k14.0 matches a 3/4" orifice 

The k-factor is a way that we describe the orifice size. It is a number that relates the flow that will discharge through a sprinkler to the pressure of the water at the sprinkler.  

In the old days when MTV played music, we used to refer to sprinklers with a k-factor of 5.6 as being “1/2-inch sprinklers”, or k8.0 sprinklers as being “17/32 inch sprinklers”. We no longer use this terminology, because the k-factor is a more simple and consistent way to represent the orifice size of a sprinkler. 

Sprinklers with a k-factor of 5.6 are considered standard orifice sprinklers. These make up the basis that we use to compare against all other sprinklers. Sprinkler with a k-factor less than 5.6 are “small orifice sprinklers”. We technically don’t have a name that lumps in all sprinklers greater than 5.6, but these often include storage and other special application sprinklers.  

PINTLES

It’s not possible to check whether standard spray sprinklers are installed with the matching orifice size in most installations just by looking at the sprinkler. But, we do have a clue to determine when there is an unusual situation that could require further investigation. 

This is related to the presence of a pintle on the sprinkler deflector. A pintle is the raised cylinder that extends above a sprinkler deflector. This pintle is a visual clue that the thread of the sprinkler is not the thread size that is expected, based on the orifice size of the sprinkler. 

For example, 1/2" thread normally applies to k5.6 orifice sprinklers.  

For larger orifices (K11.2) and larger, the thread size may vary from 3/4" to 1”.  

But if you have a smaller orifice (or a larger) than expected with a ½" thread, then you have a different K-factor. This could be the case if a system was designed with ½-inch outlets, but then remodel with some storage that uses retrofit k8.0 sprinklers on those same branch lines. The pintle is an indication that a k8.0 sprinkler is used with a ½-inch thread. 

Use of smaller orifice sprinkler can be problematic in some locations when raw water is used, as sediments and mud may obstruct and alter the water pattern discharge of sprinklers with very small orifices. 

For that reason, some Insurance companies do not recommend the use of K factor smaller than 5.6, even for light hazard occupancies 

THREAD & ORIFICE SIZE

Other parts of an evaluation that are affected by k-factors and orifice sizes is storage criteria. If we need to evaluate whether a new storage commodity is properly protected, we’re going to want to know the k-factor of the sprinklers being used. Storage criteria, such as with ESFR sprinklers, for example, will base a minimum pressure at the sprinkler depending upon the k-factor used. Starting pressure and the k-factor work together as baseline design requirements in NFPA 13 and in FM Global. 

This information can be gathered from drawings or from sprinklers in the spare cabinet box, but the only way to know with certainty what is installed is to look at the installed sprinklers themselves. While a k-factor may not be marked on the sprinkler, it can be gathered from product data once the Sprinkler Identification Number, or SIN, is read from the sprinkler deflector.

Reading the model number is not always an easy feat. It often requires a ladder or a lift, and if the sprinkler has been installed for some time, dust often concealed the etched model number on the deflector. When up close, try blowing off dust on the sprinkler and use a camera or flashlight to give the engraved model number a chance to shadow and show itself. For upright sprinklers, model numbers are often on the top of the sprinkler. Here, using a smartphone in selfie-mode can make getting a close up picture with you and the sprinkler a helpful treat. Or just get the sprinkler, your call there. 

When walking storage areas, noting the model number of the sprinkler can be useful information if we need to study the system in more depth. Taking notes by sampling each type of sprinkler by reading the SIN number on the deflector could be a helpful indicator of the storage capability of a system, and at the very least arm you with information that may prove helpful later.

I’m Franck Orset, this is MeyerFire University.