# pressure on a fire system



## Plumber Jim (Jun 19, 2008)

I have a job to replace a leaking prv on a fire sprinkler system. and was wondering is there a setting that is a norm? I don't know for sure what the orginal one was set at. the call out was because it was leaking. the factory setting on this one is 55 psi with a max setting of 75. any suggestions?


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## skitian (Apr 5, 2011)

I've never seen a PRV on a fire system, I would think you would want maximum pressure. Don't they test those to 250 psi. Since the pressure is, hopefully, static, it's not like you would have to worry about the water etching the pipe with to high of pressure.


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## RealLivePlumber (Jun 22, 2008)

I'm sure your insurance co. Would not want to see you asking that question.

Let the fire protection co. handle it.


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## Plumberman (Jul 7, 2008)

Fire suppression systems are boosted after going through a backflow then supply the building it's protecting. I see them at usually 200-250 psi. 

What type of building?


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## HOMER (Jun 5, 2011)

Don't they test those by water volume at the stand pipes ?

Have a flow guage for stand pipe connection ?


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## Tommy plumber (Feb 19, 2010)

According to NFPA 14 7.2 "The maximum pressure at any point in the system at any time shall not exceed 350 psi."

However, 7.8.3 states that if the "static pressure at a hose connection exceeds 175 psi, an approved pressure-regulating device shall be provided to limit static and residual pressures at the outlet of the hose connection to 100 psi for 1 1/2" hose connections available for trained personnel use and 175 psi for other hose connections." This is for Class I and Class III facilities.

Class II facilites are: 65 psi minimum pressure and 100 psi maximum.

Look also at 7.8.1 and 7.8.2. There it states a min. pressure of 100 psi for 2 1/2" hose connections and a min. of 65 psi for 1 1/2" hose connections.


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## Plumber Jim (Jun 19, 2008)

I will be on site tomorrow to take a look at it. All i know at the moment is that it is leaking and is a 1 1/2" conbraco 36H-207. and they said that their fire guy told them to call their plumber. I will see if this is indeed a fire line or they are just confused.


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## Tommy plumber (Feb 19, 2010)

Let us know. In my state (FL) fire standpipes fall under the scope of the license of a plumber. For fire sprinkler systems, however, a fire contractor's license is needed. There are hydraulic calculations to figure out and so forth. 

It sounds like you are describing a fire standpipe.


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## Plumber Jim (Jun 19, 2008)

Ok, I got out there and I see why their fire guy told them to call a plumber. It was the main. Not the fire sprinkler supply. Thanks for the help.


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## sprinklertech (Oct 24, 2010)

In regards to fire sprinkler and standpipe systems I'll try to clear it up a little.

*But first a word of warning. Make sure you are licensed to do the work and as previously pointed out make darn sure you have insurance coverage for fire sprinklers.... if something happens it could get extremely costly... something goes wrong and you can do a million dollars damage real fast.* 

For most systems hydrostatic testing is to 200 psi or 50 psi above the normal operating pressure whichever is higher.

Since standard sprinkler heads are rated to a maximum of 175 psi working pressure under normal conditions the highest pressure you would see is 225 psi.

If static water pressure from the city or fire pump is 90 psi the hydrostatic pressure would be 200 psi. If the static pressure from the city or fire pump is 165 psi then the hydrostatic test pressure would be 215 psi.

There are exceptions to the 200 psi hydro in both NFPA #13 (full systems) and NFPA #13R which are:

From NFPA #13



> 16.2 Acceptance Requirements.
> 16.2.1 Hydrostatic Tests.
> 16.2.1.1 Unless permitted by 16.2.1.2 through 16.2.1.6, all piping and attached appurtenances subjected to system working pressure shall be hydrostatically tested at 200 psi (13.8 bar) and shall maintain that pressure without loss for 2 hours.
> 16.2.1.2 Portions of systems normally subjected to system working pressures in excess of 150 psi (10.4 bar) shall be tested as described in 16.2.2.1 at a pressure of 50 psi (3.5 bar) in excess of system working pressure


Why are these systems tested to 200 psi if the city pressure is only 45 psi? Most systems having more than 20 sprinklers have fire department connections where standard operations call for the fire department to use the pumper truck to boost pressure in the event of a fire. Most fire departments will boost to 150 psi and the whole reason for the test is to make sure a fitting isn't blown apart impairing the system.

Some people think we test to insure no drips... drips or small leaks isn't the main reason, the owner will take care of that... the main reason is to insure the integrity of the system when charged during fire fighting operations.

From NFPA #13D (home dwellings)



> 4.3* Hydrostatic Tests.
> 4.3.1 Where a fire department pumper connection is not provided, the system shall be hydrostatically tested for leakage at normal system operating pressure.
> 4.3.2 *Where a fire department pumper connection is provided, the system shall pass a hydrostatic pressure test performed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.*


I can not imagine a 13D system having a fire department connection, so far I have never seen one. My guess is 99.9% of the 13D systems don't have FDC's so the standard required hydro would be to simply turn the water on.

About PRV's.

You are only going to find a PRV in two instances.

One would be a main relief valve on a diesel engine driven fire pump (NFPA #20) and these will be big PRV's. On larger pumps I am talking 6", 8" and 10" with open waste cones. On larger pumps a discharge of 500 to 1,000 gpm can routinely expected. Not all diesel engine driven fire pumps are required to have one but NFPA #20 is beyond the scope of this forum so I won't waste your time.

On standard sprinkler systems you will find small (I use 1/4") pressure relief valves on gridded wet pipe systems.

From NFPA #13



> 7.1.2 Relief Valves.
> 7.1.2.1 Unless the requirements of 7.1.2.2 are met, *a gridded wet pipe system shall be provided with a relief valve not less than ¼ in. (6.4 mm) in size set to operate at 175 psi (12.1 bar) or 10 psi (0.7 bar) in excess of the maximum system pressure, whichever is greater.*
> 7.1.2.2 Where auxiliary air reservoirs are installed to absorb pressure increases, a relief valve shall not be required.


All PRV's I use are factory set to 185 psi.

Concerning "auxiliary air reservoirs" these would never be used. They make them, we do sometimes use them on anti-freeze systems, but they must be UL Listed for fire protection service and that makes them expensive. Better to spend $50 on a 1/4" PRV than $600 on a air reservoir.

You will never see a PRV on an NFPA #14 standpipe system. You can sometimes see pressure regulating valves but not pressure relief valves... there is a huge difference between the two.

Again most of you guys are limited with residential one and two family dwellings and even here you want to make damn sure you have the coverage on your liability insurance before you do anything. Fair is fair, I have coverage for sprinklers but if I changed a leaky faucet on the side I don't... works both ways so please check to cover yourselves.


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## DJ AquaMaster (Aug 19, 2011)

Hi Jim 

Usually prv's are installed on sprinkler system that were designed by someone  engineer or such  - that's why you dont want to mess with pressures . I would test existing prv and set new one just like old was set - 85 psi would be ideal if you are not able to determine desired psi on existing


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## abudgetplumb (Aug 22, 2011)

genius i love talking or reading plumbing


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## sprinklertech (Oct 24, 2010)

DJ AquaMaster said:


> Hi Jim
> 
> Usually prv's are installed on sprinkler system that were designed by someone  engineer or such  - that's why you dont want to mess with pressures . I would test existing prv and set new one just like old was set - 85 psi would be ideal if you are not able to determine desired psi on existing


If it is a combined system I can't see any reason for a prv ever. Every time the toilet, or the bathroom faucet drips, any excess pressure build up is released.

FYI on a commercial system a prv will be one of two settings. 175 psi or 185 psi *no exceptions ever* and even then the only time any prv is required is a wet gridded system. If you see a prv on a non-residential system and the setting is other than 175 or 185 it is wrong.


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## Wafflefryer (Nov 4, 2010)

On the residential side of things, it's not unusalt to see a 75/25 PRV installed on the waterline if upstream pressures exceed 80psi. It's my understanding that this is to protect the plumbing fixtures in the house.

I ever case where a sprinkler system share the incoming line with the domestic water, the location and pressure setting of the PRV is critical.

For instance;

Pretend the city supply has a static pressure of 120psi. Then lets say that there will be a total residual loss in the supply pipe of 30 psi.

Scenario 1 PRV located at the city connection;
If a 75/25 prv is located at the tap to the city main, then we no longer have 120 psi but a maximum of 75 psi to work with. 
Next we must factor in the friction loss across the PRV. An off-the-shelf 1" prv will usually be around 25 psi.
This bring the flowing pressure down to 50psi.
Since the prv is located at the street, we still have to factor in friction losses through the supply pipe which we are saying is 30psi.
This leaves us with only 25PSI at the base of the riser to work with.

Scenario 2 PRV Located at the base of the riser
120 psi at the street
30 psi loss in the underground leaves us with 90psi at the base of the riser
we still only can use 75psi because of the PRV
Then we'll subtract the friction loss across the PRV again of 25psi
This leaves us with 50psi at the base of the riser.

Scenario 3 PRV on the domestic line at the base of the riser after the FIRE/Domestic split
120 psi at the street
30 psi loss in the underground leaves us with 90psi at the base of the riser
since the prv is on the domestic split and not the fire split we have 90 psi at the base of the riser


Even though NFPA 13D does not require a flow test, I highly endorse them. Sometimes there are things in an underground pipe that nobody knows is there and dont really surface until the system fails. A flow test from the remote sprinklers is a good way to find these problems.


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## sprinklertech (Oct 24, 2010)

Wafflefryer said:


> On the residential side of things, it's not unusalt to see a 75/25 PRV installed on the waterline if upstream pressures exceed 80psi. It's my understanding that this is to protect the plumbing fixtures in the house.


Understand I have never done, or will I ever do, a multipurpose system. That's should rightfully belong to the plumber.

From NFPA 13D "Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes" - 2002 Edition



> 5.2.5.2 Fittings used in sprinkler systems other than those addressed in 5.2.5.3 shall be designed to withstand a working pressure of not less than *175 psi* (12.1 bar).
> 5.2.5.3 Nonmetallic fittings used in *multipurpose piping systems* not equipped with a fire department connection shall be designed to withstand a working pressure of not less than *130 psi* (8.9 bar) at 120°F (49°C).


There may be some confusion on what a pressure relief valve and pressure regulating valve is.

A small (1/2") relief valve commonly found on fire sprinkler systems *http://www.vikinggroupinc.com/usrelated/agf/m7000.pdf*

The only other place to ever see a relief valve would be the discharge side of a fire pump and most likely a diesel engine driven fire pump.

The valves will be big.

*http://www.cla-val.com/pdfs/E-750B-4KG1_Fire.pdf*

From NFPA #20



> 2-13 Relief Valve.
> 2-13.1*
> Where a diesel engine-driven fire pump is installed and 121 percent of the net rated shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation, exceeds the pressure for which the system components are rated, a relief valve shall be provided.
> 2-13.2
> The relief valve size shall not be less than that given in Table 2-20. (See also 2-13.7 and A-2-13.7 for conditions affecting size.)


GPM / Minimum Relief Valve Size
500 / 3"
750 / 4"
1,000 / 4"
1,250 / 6"
1,500 / 6"

I could be wrong but are some calling a pressure regulating valve a relief valve? I think it plumbing you would be using pressure regulating valves something like this *http://www.watts.com/pages/_products_details.asp?pid=776*

I've never installed one of those. Everything we use on commercial systems is rated to a working pressure of 175 psi and if we had something more, say 225 psi city pressure, there are sprinkler heads available rated to a working pressure of 250 psi.

As an example the *Viking MicromaticHP*® Standard Response Pendent Sprinklers (High Pressure) *Maximum 250 PSI* (17 bar) WWP are rated to 250 psi but the owner won't be liking the price.

Also, be advised I don't know of any residential listed sprinkler that has a higher rated working pressure than 175 psi.

The only place I've ever used a regulating valve is the 2 1/2" hose valves on standpipes like on of these *http://www.guardianfire.com/pdf/firehosevalves5000_c.pdf* (Most commonly used is at the bottom of page).

I know most of you guys knows the difference but maybe someone here didn't. Also sometimes we call something not exactly right but within the trade we all understand.


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