When performing hydraulic calculations, do I need to account for the length of the barrel of a dry sprinkler?
The sprinkler itself starts at the threads, but the length can sometimes be quite long before water hits the orifice of the sprinkler.
Under NFPA 13, under friction loss, the closest I can find says "friction loss shall be excluded for the fitting directly connected to the sprinkler."
Thanks in advance.
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5/10/2022 07:18:21 am
5/10/2022 08:07:26 am
If you're using 1" dry pendents and also using 1" drops for other pendents the calculations is the same. If I was using a 3/4" dry pendent I would certainly put the dry barrel length in, but in most case I'm just doing it for fab purposes.
5/10/2022 08:10:36 am
It has always been my understanding that the way the dry sprinklers are tested and listed they have already factored in the length during the testing process. So based on their listing and testing it is the same for a dry sprinkler with a 12” barrel as it would be for a standard pendent in a bell or ell. You don’t add the drop length to your calculations as friction loss.
5/10/2022 08:33:34 am
I have always been under the understanding that the length of the sprk is factured in as well.
5/10/2022 08:34:58 am
There is a significant hydraulic difference between a 4'-0 dry barrel and a 1'-0.
5/10/2022 08:36:26 am
Many of the cut sheets have this kind of language (this was taken from a Viking Cut Sheet) which means you don't need to adjust for the dry length per NFPA 13-19' Section 184.108.40.206.3 - "Flow from a sprinkler shall be calculated using the nominal K-Factor except that the manufacturer's adjusted K-Factors shall be utilized for dry-type sprinklers"
5/10/2022 08:41:10 am
Yes the length of the matters significantly for hydraulics. As the length changes the K-Factor changes for many manufacturers on their data sheets. Secondly pay attention to the C-Factor. Lastly the exposure temperature charts will dictate the minimum barrel length. All of this information is typically listed on the manufacturer data sheets as it varies for each type and manufacturer.
5/10/2022 09:09:36 am
You need to document what k-factor being used. K-factor for the dry barrel assembly should be used and assumed at the tee-connection.
5/10/2022 09:13:54 am
The engineering behind a UL listed product probably exceeds my skill, knowledge and intelligence.
Brian Gerdwagen FPE
5/10/2022 09:15:03 am
Glenn is 100% correct, as are some others. The adjusted K factor from the manufacturer gives you the K factor at the fitting the sprinkler is attached. There is no need to add additional friction loss for the length of the barrel of the dry pendent.
5/10/2022 12:46:42 pm
5/10/2022 03:06:16 pm
When you see the size of the orifice entering and exiting the assembly well rough guess the barrel is three times the area of the orifice. Relatively little resistance to the flow.
5/10/2022 09:56:32 am
i see conflicts in the responses - my state construction office requires calculating the lengths of flexible connections to Vic's Flex Sprinklers so whether M.Newell or others are correct or incorrect, my situation requires I calc the lengths (including dry barrel). Check with your AHJ or State Construction Office and streamline your process to include the most stringent requirements ... The "costs" should be passed on to the owner anyhow so why not be safe and do it ?
5/10/2022 10:37:28 am
Vic already states in the literature:
5/10/2022 10:41:41 am
Back in 63, my father taught me hydraulic calculations. Head k factors adjusted to account for length are factored in. It hasnt changed.
5/12/2022 04:54:53 pm
Larry A Gallego
10/3/2022 11:29:18 am
Another aspect that comes into play is whether the elevation of the outlet on an 12" dry pendent is used for the calculation or is the elevation of the connection to the branchline/mains selected?
10/4/2022 09:14:51 am
I checked several manufacturers data sheets for dry pendants.
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