Here in Johnson County KS. our local water service purveyor (WaterOne) had a
54" main break on July 1st , I know that parts of this extensive system were in
excess of 20 psi residual. However as a precaution the water company issued a
boil order for over 400,000 of its customers.
I have always understood the minimum of 20 psi residual was to keep enough
pressure on the mains and taps so as to prevent contamination or a backflow
condition from occurring.
As a pumper operator during a fire I never went below 20 psi in the intake side
of the pump, unless of course we were drafting from a body of water, which
would then usually have a suction of 10 to 17 "Hg. (5 psi to 8.5 psi)
Yours truly,
Captain Frank J. Herrick
City Of Leawood Fire Department
14801 Mission Road
Leawood, Ks. 66224-9560
Office: 913.681.6788 x 26
Fax: 913.681.2399
Fire Sprinklers Save Lives, Property, the Environment, and Water - Protect what
you value most!
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Smith, Steven D.
(CSFD)
Sent: Wednesday, August 24, 2011 9:16 AM
To: [email protected]
Subject: RE: Minimum pressures in water supply; Why 20 psi?
During a sprinkler design class we were told by the instructor that the 20psi
comes from the health department and anything less than 20psi in the mains will
require citizens to boil the water to remove containments in the water.
Previously I had always heard anything less than 20psi could potentially
collapse water lines.
Steve
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of David de Vries
Sent: Wednesday, August 24, 2011 8:11 AM
To: [email protected]
Subject: Minimum pressures in water supply; Why 20 psi?
Does anyone know where the 20 psi minimum for undergound piping originated? I
have seen it in some state water regs, but have never been satisfied that it is
a sound, scientifically-based number.
I have also seen fire dept SOP's set an alert on suction pressure at the pumper
to 5 psi. Depending on the hose lay, that might equate to 20 (or 10) psi in
the main.
Dave
David A. de Vries, P.E., CSP
Firetech Engineering Incorporated
--- On Wed, 8/24/11, Letterman, Todd <[email protected]> wrote:
From: Letterman, Todd <[email protected]>
Subject: RE: Minimum pressures in water supply
To: [email protected]
Date: Wednesday, August 24, 2011, 8:27 AM
I agree with all who have responded and I'm not sure if there is hydrant
at the entrance to this place or along the street that could rob your
suction pressure. If there is a hydrant coming into the property, then
they are most likely going to start there hose lay at that point, which
may rob all the theoretical values so far. You are not going to have
much suction pressure at a 100%. If a fire takes it to that demand but
there is really nothing stating that you cant go lower than 20 unless
the water authority or other entity states other wise. It was never
stated if it is going to be a Electric or Diesel Driver or have you
gotten that far yet?
Todd Letterman
Fire Prevention Engineer CFPS
Riverside County Fire Department "Fire never sleeps"
(951) 955-5273 FAX (951) 955-4886
[email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Todd
Williams
Sent: Wednesday, August 24, 2011 5:21 AM
To: [email protected]
Subject: Minimum pressures in water supply
I am working on a new school project, where the building is 65 ft above
the water supply in the road and 760 ft horizontally. The water supply
is 54-46-1130. There is a pump planned, which I have to size. The total
pressure loss in the underground between the supply and the pump house
is approximately 30 psi. I know the general consensus (and some water
company requirements) is that the water pressure not be drawn down below
20 psi. A 500 gpm at 60 psi pump would be a good fit for this project,
but the suction pressures at the pump would end up being below 20 psi.
The supply in the public mains would remain above 20 (due to the
elevation), but would be below that in the private main at the pump
room. Any thought if this would be acceptable?
Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, CT
860.535.2080
www.fpdc.com
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