Concern with Draining Standpipes Back to Tank?

9/3/2024

We're designing a small footprint high rise with 2 stairs/standpipes, and 3" drains in the stairs for floor control valve drains and testing/verifying hose valves.

Primary water is supplied from a vertical turbine pump and tank. Local codes don’t allow direct outdoor drains so it’s either into the tank or into large hub drains.

Owner is very ‘green’ and looking for ways to reduce water usage. We’ve already got the fire pump test flows back into the tank. We’re considering flowing the stair’s drains into a hub with a bypass into the tank -- hub for system draining, tank for PRV and flow switch testing.

Is it advisable or preferable to run these stair drains back into the tank?

Concerns include flowing black, stinky water into the tank and possibly adding pipe scale into the tank

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4 Comments

Anthony

9/3/2024 07:59:58 am

You can always drain/test back to a tank, if pipe scale is an issue you could have a strainer on the inlet to the manifold and include it in the maintenance plan for cleaning it out every 2ish years?

For the smell just have the tank vent somewhere appropriate.
You could do an exhaust vent to the plumbing vent system and add in a suction vent from the immediate tank area if it's not buried.

Jack G

9/3/2024 10:37:25 am

A water storage tank for the vertical pump should already have a vent to the exterior.
The tank water is already considered “ non potable “ per NFPA 13, 22, 14.
I usually put an automatic air vent at the tops of each standpipe. This is for draining and filling of the standpipes, easier and faster and to get trapped air out of the system. I also do this to eliminate the “ boyles law factor”. I have determined that with 5% or less of trapped air, and a 10 degree temperature change or more, system pressure will double and we d get callbacks. After years of this I started putting automatic air vents at the top ( clay valve vent) . Maintenance shutting down, for repairs and filling ( with no vents ) made the pressure increase worse.
A pressure relief valve at the lowest floor of the standpipes would let excess pressure out, but do nothing for the filling and draining.
So draining the volume into the fire water storage tank is required and also saves water where municipalities do not allow draining it to sewer or the ground.
When testing the floor prvs, I use 500 psi lined hose to the 3 inch drain riser from my flow meter, and also open up a 2.5 inch plug at least a couple above my test to avoid a vacuum while the discharge water is draining. ( tends to pull the hose inside out and damaging it)

Thomas Duross

9/5/2024 01:39:07 pm

Jack-

About 10 years ago I had 5' and 10' sections of 2 1/2" hydraulic hard hose (they pump concrete through it, same stuff) with male and swivel female and that cured the collapsed hose issue. We were drawing the liner out of the hose. I have vented elbows for my flowmeters that once cracked open after testing, cure the vacuum issue in minutes. Even 20-40 stories.

Thomas Duross

9/5/2024 01:35:08 pm

Plus, the tank will (supposed to) get inspections every 5 years so grit and debris should be removed. This is good conservation of water and 'green'.

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Concern with Draining Standpipes Back to Tank?

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