Good information from Paul and Chris regarding fire apparatus pumps. If you really want to understand fire apparatus pumps and true FD capabilities, you'll need to do that yourself and not solely rely on the FD. Unfortunately, detailed knowledge of fire ground hydraulics, particularly with regard to pump hydraulics, is still rare in the fire service . Also conservation of mass (or volume in fire service hydraulics to make it simple) is often optional! As was stated, 1000-1500 gpm rated pumps are probably most common, but 1750, 2000 gpm and larger are becoming more common place. The problem is that supply line size hasn't kept up. It is not uncommon in traditional New England FDs to see a new 2000 gpm tower ladder with dual 1000 gpm master streams in a dept running with 3" supply line. In a forward lay, depending on supply line length and size, with lower pressure on the municipal side, supplying the rated volume of the pump might not always be the case. Just because a department says it has pumpers are rated at x gpm, doesn't mean they have analyzed and can deliver that volume to the pumper (unless they have figured out how to beat conservation of mass (volume more simply) and get 1500 gpm at the discharge side while supplying 1000 gpm on the suction side.
If you wanted to be sure they can provide what they say they can, you can't leave out the supply lines and hose lines between the pumper and the FDC. Also, it raises a red flag to me when a dept. states they can provide say 1500 gpm @ the FDC at even 150 psi. I always ask, how are you going to supply that and what is your pump pressure to deliver that 1500 gpm @ 150 psi to the FDC. Not many FDs run LDH to the FDC. They typically use 2 1/2" or 3" and you are looking at losses in even a short length of a pair 2 1/2" or 3" hose lines that is significant. Flow meters are not typical, so the pump operator doesn't know what he/she is flowing with a great deal of accuracy. So if he/she is pumping at 150 psi and a significant volume, you probably have quite a bit less than 150 psi at FDC. They can throttle up to 150 psi as the flow increases at the pumper, but again, if you're flowing significant volume, your less than that at the FDC. If you wanted to provide some margin for that, we should design for a FDC inlet pressure around 125 psi as standard without any additional info. That way whether the apparatus pump is at churn or more of a max flow, a 150 psi pump pressure is legit and your FDC pressure will vary between 150 and 125 psi or so (greater than your design pressure of 125 psi). If you truly want 150 or better at the FDC, you need to look at the friction loss between the pumper and the FDC, because if it is significant and it is not accounted for, a pump pressure of 150 psi isn't going to deliver 150 psi at FDC (you'll get less than your design pressure at the FDC). Some FDs will put a gauge at the standpipe connection and can communicate with the pump operator to increase/decrease pressure as required. Others don't and if you design for 150 psi at FDC and they pump it at that and no one (the designer or the pump operator) has accounted for the friction loss between the pumper and the FDC, the crew(s) on the hose line(s) may be short on pressure and may experience the resulting poor nozzle performance, etc. For those that are interested, as was stated previously, fire apparatus pumps are variable speed by varying the engine RPM. Also, most apparatus pump manufacturers use the same case and often the same impeller for multiple pump ratings with 750/1000/1250 rated pumps typically using the same case/impeller and 1500/1750/2000 using another case/impeller. All that is varied is the pump RPM through changes in the pump transmission gearing (and ensuring the truck engine has sufficient HP to drive it after losses are accounted for). Richard Malek [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Paul Sincaglia Sent: Tuesday, April 10, 2007 12:55 PM To: [email protected] Subject: RE: Manual wet standpipes First, for those of you who are not fire service types...you really need to get up to speed on the fundamentals and the tactics if you are designing what are manual firefighting components. Talk to your local FD's. They would be more than happy to give everyone a couple of hour "seminar" on the basic tactics and operations. After all, you are building stuff for them to use and they REALLY want/need it to work. Fire apparatus pumps are variable pumps with the discharge volume and pressure output being determined by the incident and the actions of the firefighters/pump operator. You can flow 100 gpm at 50 psi and then jump to 1200 gpm @ 175 psi if you want by opening valves and adjusting engine speed. You can even get the pressure in the hose line to be lower than the city pressure if you throttle your valves. The point being that you cannot and should not treat apparatus pumps like a normal fire pump. There is a human in the way and you have to account for him/her in your calcs....hence my very first comment above. That said, as someone else stated earlier, it is fairly common for fire departments to tie-in to a sprinkler and/or standpipe riser and pump at 150 psi and adjusting engine speed to maintain this until notified to do something else. This is used for two reasons. First, 150 psi is some pretty good water pressure and works very well for the majority of sprinkler systems. Second, from a standpipe point of view, 150 psi is more often than not sufficient pressure to overcome elevation and friction losses to the firefighters on the tip (nozzle). They can call for adjustment at needed...and often do. Fight the fire in the basement and provide nothing less than 150 psi, when me and my crew get done taking a beating from our own hoseline, I will come outside and use whatever energy I have left to beat the pump operator into a bloody pulp. Conversely, if you are up to many floors firefighters can take a beating from insufficient pressure too...hence the code requirements. This is the reason you do the calculations...it prove whether your design is capable of providing adequate pressure and volume with the human factor in the system. We (my engineering firm) always assume that the water supply curve for a manual standpipe is 150 psi static, 150 residual, flowing the pumps rated capacity. For most designs this is ample...but you have to know what the pump capacity is (most today are at least 1000 gpm...but not all). If your demand is more than 1000 gpm, you need to get the info from the fire department directly...do not assume! If it turns out that to provide adequate volume and pressure at the top of the riser requires a tie-in pressure greater than 150 psi, make the FD aware (in writing) and mark it on the standpipe connection so that any responding pumper can read and knows what is needed. You can not assume that the first responding fire truck will the one closest or even from the same town. As for total water volume you have to meet the code requirements. No truck caries enough water. You have to have adequate city water, a tank, a pond, a river or a tanker (a "tender" to you west coasties) shuttle or a combination of them to meet the volume demand. I hope that helps. Paul Sincaglia, P.E. President, Firesafety Solutions, Inc. And Lt. Chagrin Falls Fire Department. _______________________________________________ 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)
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