Art, That was a good point regarding smaller systems and especially when the application is the pump(s) supply directly into the above-ground deluge piping. I was referring more so to larger campus style arrangements where the pumps are remote from the deluge systems via underground mains and there are often larger jockey pumps on the system (100's to low 1000's of gpms worth). In that case you don't necessarily see the larger pressure drop instantaneously at the fire pumps.
I was interested by the question of reaction of the larger main network to deluge valve trip. I think in that case the compressibility/bulk modulus of water might come into play. If water was truly incompressible, you would see a more dramatic, instantaneous pressure drop. Water is difficult to compress, but compressible. I ran a calculation for one of the larger sites I have had experience with and there is about 60 cu ft. of compression of the water in that system. That would be enough expansion to fill about 300 ft. of 6" pipe. And then there probably is some frictional impact as the water expands and travels through the pipe and pushing some air out of the way, etc. And there is the issue of pressure transients in the system, etc. When I was doing some google searching on the topic, one site that was discussing the compressibility of water and indicated that if water wasn't compressible, the world's oceans would be 30 ft. or 30 m (I can't remember which) higher than they are!! I thought that was quite an interesting fact as generally speaking we consider water incompressible. Richard Malek [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of art Sent: Thursday, September 06, 2007 11:00 AM To: [email protected] Subject: RE: Fire Pump Selection - Another Question When the deluge valve trips the pressure drops to nearly "0" for a few seconds until a pump spools up. There is a big surge to fill the system and equalize pressures. Both pumps will start on a pressure drop unless there is a time delay built in. Art @ ATCO Fire -----Original Message----- Subject: RE: Fire Pump Selection - Another Question Don't forget that check valves remain closed until pressures equalize ! glc -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Richard Malek eature and interaction of such options. On the issue of the two pumps meeting the demand, I see two scenarios. If the pumps are identical, supply to the discharge flanges and piping to a common point of the system are the same, each pump will supply essentially 50% of the demand. You could do some hand calcs to ballpark your pump sizing, etc. However, if you are going to use different pumps (different gpm, pressure, or the same size from different manufacturers - different curves) or the supply/discharge arrangement is different for identical pumps, you would need to develop a combined water supply curve. It would difficult to determine exactly where each pump will settle out on its curve and how much each will contribute to the supply without creating the combined curve (supply) and running a supply calc on the deluge system. Once you know where on the combined supply curve you are operating, you can back out how much each pump is contributing. Any combination where each pump is operating within the 150% of rated max is OK. Well, I hope that helps and if I missed something or I'm off in some way, someone will probably jump in. Rich Richard Malek [EMAIL PROTECTED] _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
