You don't give your location,so we don't know the actual Fire Rules at your Subdivision.

One problem with a house fire, is that you may well lose the electric supply, by the cables being burnt through, or the electric supply being cut off by the Fire Brigade on their arrival.

In many jurisdictions, the Fire Brigade do cut the electric supply, before spraying the property with water, to prevent electric shock to the firemen, or those standing around nearby.

Disregarding the above situation - of no electricity at the time of a fire, it is best to use a reciprocating (push/pull) piston type pump, which pumps water into a pressure tank, and a pressure switch on the tank, which stops the pump when the desired pressure is reached.

The pressure tank has air which is compressed above the water, thus maintaining the required pressure for a short time, while the sprinkler/sprinklers is/are actually sprinkling during a small fire.

If your subdivision/local Authority rules permit you, and you want water at 78psi for some time while the power is off, you need to install a steel framed tower, with a large water tank on it, kept full via that pump.

You then have a short calculation to establish the tower height, so that the 78psi pressure is maintained.

The water tank on the tower situation is not for everyone, because of freezing in winter, earthquakes, and general unsightliness, of course.

You then have a short calculation to establish the tower height, so that the 78psi pressure is maintained.

I had to laugh at this.... he needs a 250 foot high tower in his back yard, needs a red beacon for aircraft, has to support 5000 gal of water at 8 lbs/gal......

I think he can build a house in another town cheaper.....

Now if he wanted a realistic solution, install a gas engine driven booster pump with exhaust carefully piped outside. This engine would be SAFER it were PROPANE. A wild guess is an 8hp gas engine with a pump capable of at least 90 psi discharge AND at the total GPM delivery potential of all the sprinkler heads, the installer HAS this info.

Are you sure about the sprinkler system requiring 78 psi to operate this seems very high most sprinkler systems will operate between pressures maybe the 78 is maximum. If however you need 78 minimum you cant just boost the pressure from the mains without a storage tank. If you try and suck water from the mains directly the pump will run dry and seize very quickly.

If you try and suck water from the mains directly the pump will run dry and seize very quickly.

Well not quite, first of all, it wouldn't "run dry", maybe go into cavitation. But this has been done before, the check-valve and pressure regulator represent the biggest pressure drop but you'd be surprise what you can pull through main.

And you can indeed do this without a storage tank, its been done before. The pump will seek it's own operating curve dependent on resistance and flow. When the building is on fire, no one worries about running my pump at maximum efficiency...just "please make the sprinkler heads squirt!"

Hi, Sniccus!

I was under the impression that a limiter of some kind had been placed on the mains, restricting the flow to a specific pressure. If the draw by the blogger's pumps exceeds that pressure, wouldn't there be a danger of the mains running dry?

Mark

I was under the impression that a limiter of some kind had been placed on the mains, restricting the flow to a specific pressure. If the draw by the blogger's pumps exceeds that pressure, wouldn't there be a danger of the mains running dry?

This limiter would only be a back-flow preventor so that a customer couldn't "poison" a main. They even have little back-flo devices on hose bibs at campgrounds and outdoor spigots now.

Water companies seldom even offer a pressure regulator. (Liability issue). Their pressure is typically 70 psi to 110 psi. This fella's pump can't suck the main dry.

Storing water is not realistic either. I've seen many rural fire companies suck a neighbor's 18,000 gal swimming pool dry fighting a fire.

Bottom line here is, draft the main if it is not illegal to do so. An electric pump is cheapest but not if the fire company is going to kill the electric, but then, you don't need your sprinklers anymore, fire company's here!

And your question is...?

So the summed wisdom in the group of responses thus far is that in order to not drain the "weak pressure" mains, a separate valve-pump fed holding tank is required; and in order to avoid its possible interruption, such a system requires its own separate power supply, separated from the potential fire by distance as well.

Would such a system benefit from a centrifugal pump on the delivery end?

Mark