k-factor and orifice size

[Ciaci]

Hi everyone,


I’m looking into the compatibility between UL-listed K-factors and European classification under UNI EN 12259-1. Specifically, I’m reviewing a Viking upright sprinkler (presubimely marked 5.6 gpm/√psi), with the typical UL listing and a 1/2” NPT thread. The orifice appears to be in the 10 mm nominal range (photo attached). According to Table 3 of UNI EN 12259-1, a 10 mm nominal orifice corresponds to a K-factor of 57 ±3 l/min/√bar. However, UL 199 allows sprinklers to be classified as 5.6 even with some variation in orifice geometry, and the unit conversion from 5.6 US gpm/√psi gives approximately 80 l/min/√bar, which seems inconsistent with the European 10 mm / K57 classification.

1. Have you encountered UL-listed 5.6 sprinklers that, due to actual geometry, fall within the K57 class under UNI EN?
2. Are there known cases where K-factors "overlap" across standards?

I'm attaching:

• A photo of the sprinkler head,
• An excerpt from UNI EN 12259-1 Annex C.

Thanks for your insights — I'm trying to understand how this is approached in practice during technical evaluations or retrofitting in Europe.

 

[cdafd]

One suggestion call Viking tech support and ask the question
1-877-384-5464

 

[UFT12]

The K factor is not only depended on the orifice size rather on other factors as well such as geometry etc. A manufacturer can achieve the same K value with a smaller orifice diameter. I wouldn't pay attention to this table, rather what the spec sheets say and most importantly, what certification (listing/approval) is carries.

 

[Danefre]

K-factor is a nominal designation. It's the relationship between the Flowrate and Pressure of that specific orifice adjusted to a "nominal" value of K5.6

You cannot convert it from Imperial to SI as it's a "nominal" coefficient.

It's derived from the continuity equation for mass conservation and Bernoulli's theorem but heavily simplified. Look into that for more info.

Follow the listing!