FDC Tied-In Upstream or Downstream of PRV? 2

[Haldorson]

Hello all,

Consider a highrise equipped with a booster pump and two PRV's, one serving the dry zones in the parkade and one serving the Class I standpipe system. The PRV supplying the dry zones is set to 165 psi, the PRV supplying the Class I standpipe is set to 240 psi.

From what I understand we have two options with respect to the tie-in locations of the FDC's:

(1) Tie-in both required siamese FDC's downstream of the booster pump and upstream of both PRV's, OR
(2) Have a total of four siamese FDC's. A low and high pressure FDC for each remote FDC staging location. All FDC's are tied in downstream of both the booster pump AND the appropriate PRV's (ie, max pressure FDC's of 165 psi downstream of PRV serving the dry zones and max pressure 240 psi FDC's downstream of PRV serving Class I standpipe).

Thoughts?

Also, if the above is true, is the only advantage of using a high and low pressure FDC to reduce the run of 4" back to the valve station to tie-in upstream of the PRV's?

Thanks.

 

[cdafd]

The standpipes are supplied by the fire pump?

If so looks like option 1 is the way to go

 

[LCREP]

No matter what option you use, make sure you connect a pipe to a test header past the PRV so they can be flow tested at the maximum flow of the system. Also install a sign with the required psi and GPM after the PRV. The PRV'S will be required to be flow tested annually as per NFPA 25 2014.

My option would be option 2 so if the PRV fails the FD can supply the system. If you go with this option make sure you post the required GPM and PSI at the FDC for the fire department.

I did not investigate your options I am just providing feedback on what I think should be done based on problems I see in the field as an insurance engineer.

 

[Haldorson]

Is there anywhere in NFPA 13 or 14 that mandates a FDC MUST be installed downstream of a system PRV? If not, why on high and low pressure zoned highrises does anyone bother with high and low pressure FDC's? Why not just have a high pressure FDC and tie that into the system downstream of the pump and upstream of any PRV's?

 

[LCREP]

Hal,

I have no idea I did not research the codes for you. What I see is PRV in the field NEVER have the info required to test the PRV namely the required pressure before the PRV and the psi and GPM after the PRV. I see this as a significant problem that NFPA 25 addresses but is not enforced and many times not done. Regardless if it is a PRV on a floor or a standpipe valve or one for an entire system they are not tested and no one has a clue what is required. All it takes is dirt under a seat, not set properly and we are guessing if we have enough or too much pressure.

I do not see the required pressure gauges before and after the PRV, the test valve to flow the water past the PRV and the most important part no drain to flow the required water. How do you flow test a PRV on the 15 floor sprinkler riser with a required flow of 150 GPM with no drain ?

I do not know if you recall a high rise fire in Philly in 1991 at Meridian Bank Building where we lost 3 brother firefighters. This fire had a lot of things that went wrong, one of the contributing factors was PRV's NOT set properly, see link and details below.

This problem is still a problem in the USA. I can not tell you how many high rise buildings my staff looks at on a daily bases that the required NFPA 25 are just not being completed. The PRV tags are not filled out and many times the info is not available on site.

So why not connect the FDC past all this stuff so the FD has an adequate water supply?

http://www.usfa.fema.gov/downloads/pdf/publications/tr-049.pdf

Improperly installed standpipe valves provided inadequate pressure for fire department hose streams using 1-3/4-inch hose and automatic fog nozzles. Pressure reducing valves were installed to limit standpipe outlet discharge pressures to safe levels. The PRVs were set too low to produce effective hose streams; tools and expertise to adjust the valve settings did not become available until too late.

 

[LCREP]

More info from the Philly fire and PRV'S from the above report.

When the PRVs were originally installed, the pressure settings were improperly adjusted. Index values marked on the valves did not correspond directly to discharge pressures. To perform adjustments the factory and field personnel had to refer to tables in printed installation instructions to determine the proper setting for each floor level 4. For more detailed information about PRVs see Appendices D and E.

Several fire department pumpers were connected to the fire department connections to the standpipe system in an attempt to increase the water pressure. The improperly set PRVs effectively prevented the increased pressure in the standpipes from being discharged through the valves.

The limited water supply prevented significant progress in fighting the fire and limited interior forces to operat- ing from defensive positions in the stairwells. During the next hour the fire spread to the 23rd and 24th floors primarily through autoexposure, while firefighters were unable to make entry onto these floors due to deteriorating heat and smoke conditions and the lack of water pressure in their hose- lines. Windows on the 22nd floor broke out and the 23rd and 24th floor windows were subject to autoexposure from flames lapping up the sides of the building.

 

[Sdpaddler50]

I know you are looking for an answer re the FDC, and I don't know the answer.

But, LCREP is dead on re his posts. Getting these PRVs installed properly so they can be tested is a much larger issue than where the FDC goes. Key point, a PRVs is sitting there in the closed position unless the downstream pressure drops which causes them to open.

If anyone is interested check out fm data sheet 3-11 for details.

Hopefully someone can answer your question re the FDC.

 

[Sdpaddler50]

Where I work, most High rises are flow testing their 2 1/2 in hose connection PRVs on the standpipe by flowing water down a hose in the stairwell. But, the PRVs supplying the sprinkler systems sit there for years, and never full flow tested. If the codes adopted fm 3-11 for the design and install, the situation would be resolved.

 

[LCREP]

From NFPA 25 2011 Ed

For sprinkler per floor

13.5 Pressure Reducing Valves and Relief Valves.
13.5.1 Inspection and Testing of Sprinkler Pressure Reducing Valves. Sprinkler pressure reducing valves shall be inspected and tested as described in 13.5.1.1 and 13.5.1.2.
13.5.1.1 All valves shall be inspected quarterly to verify that the valves are in the following condition:
(1) In the open position
(2) Not leaking
(3) Maintaining downstream pressures in accordance with
the design criteria
(4) In good condition, with handwheels installed and
unbroken
13.5.1.2* A full flow test shall be conducted on each valve at 5-year intervals and shall be compared to previous test results.
13.5.1.2.1 Adjustments shall be made in accordance with the manufacturer’s instructions.
13.5.1.3 A partial flow test adequate to move the valve from its seat shall be conducted annually.


For a master PRV one that controls an entire standpipe and or riser, this is the one that does NOT get done most of the time, if so at most every 5 years.

As I have said how do you comply with # 2 below if it is never posted, and the hydraulic calculations are long gone? If the AHJ only enforced this section it would make things so much easier. This is going to come back and get some AHJ one day when another brother dies because no water is coming out of the outlet to the hose or sprinklers.

PLEASE ENFORCE THE CODE!!!!

13.5.4 Master Pressure Reducing Valves.
13.5.4.1* Valves shall be inspected weekly to verify that the
valves are in the following condition:
(1)*The downstream pressures are maintained in accordance with the design criteria.
(2) The supply pressure is in accordance with the design criteria.
(3) The valves are not leaking.
(4) The valve and trim are in good condition.
13.5.4.2* A partial flow test adequate to move the valve from its seat shall be conducted quarterly.
13.5.4.3* A full flow test shall be conducted on each valve annually and shall be compared to previous test results.
13.5.4.4 When valve adjustments are necessary, they shall be made in accordance with the manufacturer’s instructions.

 

[Haldorson]

Thanks for all the responses. Very useful and much appreciated.