Since your only using it to restore the lower operation pressure in the
mains why use a 2.5" device? The smaller a device the lower the impact if it
fails open. Also if the only usage on this system is for fire, you'll have a
small spike at start up, but a very low volume to deal with to return it to
155 / 160 Psi. If the system feeds domestic / industrial uses wouldn't that
relieve the excess?
Thom McMahon
Firetech, Inc.
2560 Copper Ridge Dr
Steamboat Springs, CO 80488-2136
Tel: 970-879-7952
Fax: 970-879-7926
----- Original Message -----
From: "George Church" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, September 19, 2007 6:05 PM
Subject: PLD and PRV
We've noticed the PLD's we've installed allow brief surge of
overpressurization while the diesel starts up, builds pressure, and for
the
time it takes the PLD to react, there's an inrush of some of the churn
pressure until the governor kicks in and backs it down. Guy at Clarke
confirmed this.
We have a project with what is possibly fragile UG in many sections of the
facility. We're trying to keep it, and the related interior systems, from
creeping up to high pressure (isn't that why we have the PLD?). This
particular site is getting twin 2,000 @ 150 diesel vertical turbines,
which
feed a large looped yard system, in turn feeding -oh, couple dozen risers
scattered around.
We're thinking a small (2.5"?) Relief valve located past the pump
discharge
valve, just before it drops into the yard system, PRV discharge piped back
to the reservoir, set point 5 PSI above the PLD, set adjustment on
reaction
time to ASAP setting, so it will bleed off the excess pressure as soon as
possible. We think the size of the yard loop- complete with sectionals,
hydrants, etc.- will absorb the shock with only a small amount of it
getting
into the interior systems. If some does, 1/2" relief valves on the grid
will
take care of anything > 175. But we want to be able to have the UG drop
back
to the 155~160 range as soon as possible.
Since the twin pumps go into one yard system, the small PRV only has to be
installed on one of these. Since its relatively small, even if it failed
OPEN the loss wouldn't de-rail the train, we have 150 @ 4,000 when
combined,
and demand is about 150 @3,000. Assuming the 2.5" PRV stuck open wouldn't
flow more than 1,000 GPM, it could drop the water back in the hole to be
re-pumped all day long.
Both pumps will start remotely from elec detection systems on these large
demand systems, and on pressure drop for the conventional wets.
Yes, the owner has authorized high pressure testing of the UG, still
doesn't
mean we can slam the heck out of it or let it sit at 175+ and not see a
main
break in a couple yrs.
Any other thoughts from those with some PLD experience?
glc
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