Water Supply Below 20 psi: Chart Entire System?

10/28/2019

We have a project which is on a steep slope (the bottom of the site is about 120 feet lower than the top of the site). If we attach a fire main to the bottom of the site, the fire pump we have won't have much issue with keeping the city pressure at a 20 psi minimum or above.

If we attach to the water grid at with the fire service main at the top elevation of the site, we will probably need a suction control valve in order to keep the city pressure at 20 psi at the top elevation since the available water supply is so low.

My question is - if we pull pressure on a city's system at the low elevation, do we have to chart and consider the rest of the water supply network?

There's a chance if we pull the water supply down to 20 psi at the lower elevation that the system at the higher elevations would be well below the 20 psi due to elevation pressure loss. Thanks for your input!

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3 Comments

Wayne Ammons

10/29/2019 07:11:09 am

I'm trying to visualize what the underground piping looks like on your project from the connection to the city main to the fire pump and building being protected. Are there any backflow preventers and at what point does the water become private and not controlled by the local water purveyor?

I have seen the pressure at the pump inlet drop below 20 psi many times but the pressure remains above 20 psi at the connection to the city main and/or backflow preventer, which is where it can be argued the minimum 20 psi rule is effective.

ANON.

11/6/2019 08:15:27 am

In this case if the tap at the street gets down to 20 psi, then portions of that same city system just up the street (at 120 feet higher elevation) should be pulled well below the 20 psi, right?

I don't know how much of the city's system we need to account for, but I would presume pulling the system down to 20 psi at the lowpoint would cause issues for the same system nearby that is at a higher elevation.

Extractors Pump Vancouver link

5/4/2020 10:04:40 am

I'm trying to visualize what the underground piping looks like on your project from the connection to the city main to the fire pump and building being protected. Thanks for this wonderful article . This is a great post; I will share as much as I can.

Water Supply Below 20 psi: Chart Entire System?

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