When to Calculate Flexible Armovers in Retrofit?

1/13/2025

From my AHJ perspective and in regards to flexible drops and tenant improvements, where you typically don't receive hydraulic calcs, how are you then accounting for their equivalent lengths and friction loss?

I know some AHJ's require new calcs whenever these are being used period. I'm interested to see how others handle this. Thank you!

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15 Comments

Dan Wilder

1/13/2025 07:06:21 am

All of our AHJ's require calcs if there were no flex hoses previously on a project as there are so many options and lengths for the hoses that exceed what the hard pipe eq. length was originally.

We just use the VS-2's as these are listed as a non-calc required flex hose for the larger projects (their cost vs profit point doesn't make sense for smaller projects) and the smaller projects we just hard pipe.

https://assets.victaulic.com/assets/uploads/literature/10.93.pdf

1/13/2025 08:27:57 am

Our AHJs also require calculations for flex hoses where hard pipe was originally designed and installed.

You can make a case for flex hoses with no additional calculations if you use short hoses with a low number of bends that is close to the same friction loss as a return bend that is installed, but the AHJ can ask to see as-built drawings and hydraulic calculations from the base building (which we all know rarely exist for older systems) so we typically plan for a new flow test, surveying, drawing, and recalculating existing system modifications that change from hard pipe to flex hoses.

As mentioned, the VS-2 hoses are a "work around" for recalculating, but they're pretty expensive and depending on the project size it may wind up costing more to buy these than to recalculate the project to use the Victaulic AH2 hoses.

[WSF] Dan Wilder

1/13/2025 08:33:44 am

I will also add that we are also required to match or beat the flex hose characteristics that are installed so we can't just use any flex hose (typically length restrictive). The inspectors are a little hit and miss with enforcement but it's getting more consistent.

Pete H

1/13/2025 07:25:44 am

In my human opinion:

If Flexes have been used at the location and previously exist:

As long as the flexible connections used in the retrofit are of the same type or a less demanding type in terms of equivalent footage, no negative effects on existing hydraulics. Especially if the earlier submission where flexible head connections were used for this application can be dated and addressed on the new submission.

If Flexes do not previously exist at the location and the hazard has not changed/increased:

A calculation should be provided for all new heads using flexible head connections. Existing heads not using such connections should still be calculated as hard piped.

Flexes do not previously exist at the location and the hazard significantly decreased (like formerly ESFR outlets are now feeding a light hazard system below):

You probably still should calculate it, but I also can't see any likely system where the demand on the system's hydraulic characteristics increases during this change.

Glenn Berger

1/13/2025 08:16:37 am

It all depends on the extent of the retrofits and if the water supply conditions are different.

1/13/2025 09:15:55 am

Where we are adding flex drops to a system where there previously were none, where the existing system is old and no hydraulic calculations are available- I understand the need for calculations. Example- we did a grocery store where the overhead was scheduled and we added a ton of flex drops and calculated them and had to use fewer max bends to make them work. This example makes sense to me.
However, when we are adding flex drops to a system where the existing overhead is ESFR that demands 1500-2000 gpm and is supplied by a fire pump, I personally think it is a little ridiculous to require calculations. Recently had to do this for a few TI's. We have consistently been able to use 5.6 EC pendents on flex drops calculated at the max equivalent length and still be ~150% over the demand. Frankly, I feel that this should be obvious considering the demand for an ESFR system vs the demand of a light hazard system. In these situations, I do not agree with the necessity to provide calculations so long as the original system has been accepted by the AHJ and the fire pump has been maintained as required.
There are obviously situations in between these ends of the spectrum as well. Just my opinion.

Anthony

1/13/2025 10:11:44 am

I think calc's are required every time. 20-some-odd feet of extra 1'' pipe is a lot for who knows what kind of sprinkler. If I have a system with an original safety factor of 2 psi it won't work with flex heads. Alternatively, if the system has a 20 psi safety factor and its ~10 sprinklers I could be convinced with a good contractor not to require calcs. But this all depends on the original design.

Also, I never trust the " but it'll be a single bend radius" when it comes to field adjustments, been burnt too many times on that.

Jack G

1/13/2025 10:13:25 am

If the heads are/ were center of old tile - pattern, usually the AHJ in my neck of the woods will not make you recalculate as long as the head spacing doesn’t change dramatically.
Years ago I came up with an idea for a 1.25 flex hose to victaulic for storage and ceiling changes that would not require calcs ( 2003) - had a R&D meeting with them. they actually made it and got it approved ( 1.18 I’d), and this looks like it. I used them in AHJ jurisdictions that required them and I would present their flow data against the hard pipe data, and were accepted. Tracing the pipe back to the source of an existing system can be expensive. Philadelphia was the worst for it. Thru the years they indicated to me there wasn t much call for it, other than me.
Looks like maybe they are getting popular.

Jerry

1/13/2025 10:46:02 am

As an AHJ, we do require the calculations on a finish out where no flex drops were used prior except when using the new VS-2's. I review plans as well as do inspections here. And I would require the maximum amount of bends allowed to be calculated because in the field, the installers are not likely looking out to only using 2 bends versus 3 bends. Plus, during an inspection on a large finish out, inspectors might not catch the use of too many bends. I think Victaulic is pretty smart to make this flexible drop.

CHRIS H.

1/13/2025 11:02:32 am

Thanks for all the reply's

James E Art Fire Protection Engineer (FPE)

1/13/2025 04:50:36 pm

Flex drops are often reused when the office layout changes,
and can save a lot of pipe,
but no one will count the number of bends,
so I require the calcs to show max no of bends.

Greg Collier

1/15/2025 10:35:58 am

We always require calculations and drawing, you may use existing calculations, supported by a recent flow test with seasonal adjustment. It may require an update drawing and the conformation by the (Licensed) Design Professional indicating that the demand will less than the existing design and available water supply. All this information should be readily available if they are doing proper ITM and maintain record drawings.

Brian Cook

1/15/2025 08:17:32 pm

Victaulic came out with a flex hose that do not need calculations. It is called the VS-1 & VS-2, one is a dry flex head

Sean Kostka

1/25/2025 03:12:24 pm

Appreciate you mentioning Victaulic VS1 and VS2 Brian.

For everyone else, please find information and links below for reference to both Victaulic VS1 Dry Sprinkler and VS2 Standard Coverage Sprinkler

As it pertains to this forum topic, we will start with:

VS2 Standard Coverage Sprinkler
https://www.victaulic.com/products/vicflex-standard-coverage-sprinkler-series-vs2/
- Sprinkler and hose assembly has been calibrated as a k5.6 which does not require further calculations or use of equivalent length values
- hose lengths: 56”/ 68”
- Quick and Standard Response sprinklers
- UL Listed/ FM Approved

Victaulic VS1 Dry Sprinkler
https://www.victaulic.com/products/vicflex-dry-sprinkler-style-vs1/
- No equivalent length calculation required. (Stated on the submittal package)
- hose lengths: 38”/ 50”/ 58”
- Quick and Standard Response sprinklers
- eliminate freezes up by ensuring water stays in heated space.
- UL Listed/ FM Approved

Should any of you have any questions, please feel free to reach out.

Brian Cook

1/25/2025 04:40:45 pm

Thank you, Sean

When to Calculate Flexible Armovers in Retrofit?

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