Keep in mind that it is not the system demand that matters but the
amount of water that will flow at the lower pressure from what ever
accumulative orifice is open that triggers the 350 gpm pump.
Roland
On Apr 2, 2007, at 10:09 AM, Thom McMahon wrote:
What they are considering is requiring ALL designs be done to the
lower supply, without the Fire Pump running. The situation would
for high demand systems require additional fire pumps, which just
seems to be an expensive fix to a city wide problem. I propose
using the lower flow to design up to the point at which they are
sure the fire pump will activate, and then provide a second calc
for all flows required above that point.
If you start asking about current domestic demands ect. there are
no real answers nor anyone to ask. The city doesn't have a city
engineer. The guy that runs the water treatment plant and sewage
plant is the only "Water guy" they have. For years this has been
called the "High Pressure" main, which supplies the airport, and
hangers at the airport. The questions started flying when the
inspectors test on the new Terminal addition couldn't call for the
fire pump to activate, and just dribbled water. They solved the
immediate problem by connecting the flow switch to a signal
transmitter to call for fire pump start, but that still has about a
2 min. delay. Now they are looking at all the Airport systems,
because any small fire won't energize the fire pump. The airport is
located over a mile away from the fire pump.
Our project is half way between the airport and the fire pump, at a
new industrial park (Live work units) connected to the "High
Pressure" main
A 4 sprinkler design for the residential portion won't start the
pump, but what about the OH II 3000 SF design area? For the first
350 Gpm the fire pump won't be on, but for the total design demand
it will. That's why I proposed two calc's, since they tell me the
"Normal pumps wouldn't be able to supply the full 600 Gpm at 20 Psi
or more, not to mention the hose allowance.
Another screwy water system.Water tanks without the elevation to
get the water to the airport, hence they supply the pumps, fire
pumps to meet the "Emergency" demand, supplied from the same tanks.
Still trying to find the pressure settings for all the pumps on
this system, and their elevations, and the various tank elevations.
Thom McMahon
Firetech, Inc.
2560 Copper Ridge Dr
Steamboat Springs, CO 80488-2136
Tel: 970-879-7952
Fax: 970-879-7926
----- Original Message ----- From: "Roland Huggins"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, April 02, 2007 10:19 AM
Subject: Re: Flow test & fire pump
Are they considering IGNORING the pump demand portion of the
initial sprinkler calc since once the fire dept hooks up, the flow
is going to exceed 350 gpm?
Roland
On Apr 1, 2007, at 12:48 PM, Thom McMahon wrote:
We have a municipal water system which operates at 48 psi most
of the time, however when the flow exceeds 350 Gpm the fire pump
kicks in and boosts the system to 145 Psi, @ 2000 gpm. Whenever
a flow test is performed the results are always based upon the
fire pump flow.
As we all know most fires are contained or extinguished by one
to three heads. Obviously this isn't enough to make the fire
pump kick in.
The local Fire Chief has started to question the operation of
systems installed using the full flow of the fire pump, since
even in flow conditions over 350 Gpm it can take as long as 2
(Two) minutes for the pump to kick in. The bigger concern as I
see it is that the design for any system up to 350 Gpm should be
based upon "NO" fire pump, with two sets of calculations one for
flow up to 350, and another for flow over 350. This way we can
be sure that the sprinkler heads will have the min. pressure and
flow even if only a few go off. The other calc should be easy to
prove, as over 350 there will be a large increase in pressure
available. The caveat is that the higher flow calculation cannot
be used to reduce the pipe size below those used for the lower
calc. It is just a "Proof" calc.
Does this sound like the right approach?
No the city has no intention of changing the pump set up any
time soon.
Thom McMahon
Firetech, Inc.
2560 Copper Ridge Dr
Steamboat Springs, CO 80488-2136
Tel: 970-879-7952
Fax: 970-879-7926
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