Letters to the editor
Sam Dannaway, I read your article on AFFF for Aircraft Hangars (Plumbing Engineer, May – July) with more than a little interest since I happen to be an ex-USAF aircraft mechanic. Regarding VSR-type water flow switches, I can tell you
from 40 years’ experience that the pneumatic retards on these puppies usually start out pretty inaccurate out of the box, and only get worse over time. When it’s vital to not flow water unless there is an open head, the best way to handle wet pipe systems is with what used to be called a Gamewell Wet Kit Sprinkler Watchman. The kit super- vised both street and system sides of the check valve and maintained between 25 and 45 psi differential over street pressure on the system side of the alarm check. The main part of the system was an electric-motor dri-
ven Oberdorfer gear pump, which was controlled by a dif- ferential pressure switch. The kit contained other low pressure switches; one for Supervisory and one for Alarm. These switches, along with a pressure operated flow alarm switch, could be connected to fire alarm panels in a vari- ety of ways to meet site-specific needs. The kit part num- ber was M2700-15. The kit was discontinued by Gamewell because of the
cost difference between the kits and vane-type flow switches. Of course, most engineers and customers opting
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for vane switches probably failed to fully understand the utility and value of the kit. There was a stripped down ver- sion (minus the alarm and supervisory switches) called an Excess Pressure Pump (“jockey pump” in trade lingo). The part number for that was 26615-7. I much preferred the kit because it gave you vital infor-
mation about what you had for water right at the alarm check and a means to summon a response if the street pressure dropped too low. If you, or someone in your position, were to approach Gamewell with the idea of starting up production on the
The only problem I see with using the kit is that if a sprinkler pipe was broken or
minimize (by location) the time delay between a flow and a system dump, because you can adjust the differential pressure switch based on a site record of high and low supply pressures over some period of time.
kits again, or even doing a special, one-time batch run, they might be willing to listen. The only problem I see with using the kit is that if a sprinkler pipe was broken or developed a serious leak, you’d still dump the foam, but it’s an unbeatable way to minimize (by location) the time delay between a flow and a system dump, because you can adjust the differential pressure switch based on a site record of high and low supply pressures over some peri- od of time. I’m pretty sure Oberdorfer still makes the pump. I have
a parts list for the kit, if you’d like to take a shot at fabri- cating one yourself. For most commercial applications, a VSR is OK
because the worst thing that you can do is inadvertently empty a building and call the fire department. Cleaning up 30 – 50' of AFFF is a whole other animal, which sudden- ly helps the cost differential make a lot of sense.
Cheers, Continued on page 74 PLUMB-TECH DESIGN & CONSULTING SERVICES, LLC
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Page 72/Plumbing Engineer October 2011
developed a serious leak, you’d still dump the foam, but it’s an unbeatable way to
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