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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