4" firelines and detector check valves

[okieduck]

Hi All!
This is the first question Ive posted, so please be gentle. Im reviewing plans for fire flow check valves and had a couple questions that no one @ my job can seem to answer.
1. Other than cost, why would a commercial business or a city use a 4" fire line.
2. Ive got a fire flow detector check meter with a bypass. There is also a check valve after the bypass. Is there an absolute need for this?
Any help would be greatly appreciated.

 

[saxon]

okie, In response to question 1, I take it your talking about the riser in the building. This line size is dependant on the flow volume that is required when the sprinkler heads activate during a fire.

As for the double check arrangement on the infeed to the risers this is to keep the pressure constant in the fire system when there are pressure fluctuations in the water main. It also provides for backflow prevention into the water mains if they fail or a pumper truck is hooked up to the risers. As for your queston 2 is concerned; "Yes, a check valve is required." It's all spelled out in the Building Code.

saxon

 

[okieduck]

Saxon,
Thank you for your reply. But no, Im referring to the line from the main, since that is really the only thing we are concerned with here. This fire system comes from the main with a 4" and has a single detector check before going to the fire suppression system. Quite interesting.
The fire meter already has 3 check valves on it before the fourth goes into the facility. Two are on the main and one is on the bypass. So is that fourth one necessary?
Im sorry I didnt make my question clearer.

 

[hydrae]

okieduck

On the 4" question: if the facility just needs to sprinkle without onsite hydrants then the smaller system are not uncommon, I have seen 1",2",3", and 4" fire lines. also in the 1950's and 1960's some water suppliers only had 4" mains they used 2 port 4" hydrants. you get maybe 500 gpm out the hydrant.

on the check valve issue
check with the water provider on backflow device requirements, in water systems that I have worked with, the check valves are numerus and if you do not have all the devices, odds are you will be asked to install them soon.
It sounds to me you may not have enough check valves.

The list includes double check valve assembly (dcva) with detector bypass, the bypass also has a dcva, then the FDC has a single check that is reversable, then the sprinker alarm valve has internal check devices. just to met current req'mts
if you have a antifreeze, or a aux source booster pump then those DCVA's need to be RPVA's
also the DCVA's needed to have many blessing from USC, FM, UL and a local backflow inspector and tester.

good luck

hydrae