Thread: Small Pumps on Water System?
08-06-2001, 10:33 PM #1
Small Pumps on Water System?
I have to ask, Is it possible for example a 500gpm pump to relay of a hydrant and supply what the hydrant is rated for while boosting the pressure for a relay???
We are possibly getting a municiple water system and need info- our tankers both have pto pumps rated at 500gpm, need to know if we can use them to boost pressure for long lays or should we look at bigger pumps in the future to prepare for the change, thoughts, Idea's,problems, please reply!!Firefighter/NREMT-P/Public Safety Diver
May we ride into the darkness only to return as safe as we started!!
08-07-2001, 07:39 AM #2
- Join Date
- Dec 1999
- Desoto County, MS
Positive displace pumps (the type of most main fire pumps) will allow you to take advantage of the pressure and flow of a hydrant. You should be able to boost the pressure and in some cases suppliment the flow with your booster tank. As to whether you exsisting pumps will do what you want will depend on several factors. What flows do expect to use, what is the longest relay you expect to handle, what size hose and number of hoses you will be using both from the hydrant and on the relay itself, and the hydrant system itself. I know it sounds like a lot but it is well worth the time to preplan it before hand and know what you can handle before you get too deep into it. At any rate the 500 gpm should benfit you as long as your hydrant spacing is not to far. If you provide some more information on your needs and what your hydrant system will be able to provide, I can pass along any information I have that will help.Daron
08-12-2001, 12:23 PM #3
- Join Date
- Aug 2001
Not exactly sure what Daron was referring to with regard to positive displacement pumps. I would assume that your 500 gpm pumps are centrifugal, as are most 1901 apparatus pumps.
That aside, the answer to your question depends somewhat on a couple key factors. The first is what water supply will be available from the new water system and hydrants and two, what are your requirements(expectations) for flow (gpm) and pressure on the discharge side of those 500 gpm pumps. Tied to the second issue is how long are you expecting to relay and what size hose will be used. I would say that there is a good chance that the 500 gpm pumps could very well meet your needs with the new water system. I would analyze it before I made any decisions.
With regard to the water supply available from the hydrants. What you need, if you don't already have them, are some estimates of the water supply that will be available. What you should have are water supply graphs. A water supply graph show the various flows/pressure combinations for a water supply. The graph starts at a static condition (essentially 0 flow(or minor domestic flow))and give a static pressure. Then the graph will show the various flow points and available pressure at that point. As an example, a hydrant might have a 100 psi static pressure and then a flow of 500 gpm @ 80 psi, 1000 gpm @ 40 psi, and 1500 @ 20 psi. As you know, you don't want to take the municipal supply below 10-20 psi.
What you first want to look at is available flows. If the hydrants will have useable flows of 1500-2000+ gpms at pressures > 20 psi, then your 500 gpms pumps won't be much help in using/boosting pressure at those large flows if that is what you are looking for. However, if the hydrant flows aren't that great, or you aren't expecting to use all of the available flows, then the 500's are still in the running.
If you haven't ruled out the 500's at this point, what I would do is determine what is called a combined water supply (hydrant flow + 500 gpm pump)at the discharge side of the fire pump. The hydrant flow and fire pump are in series in this configuration, so what you do is add pressures at the same flows. For example, your 500 gpm pump has a pump curve for various RPMs. This pump curve is essentially the same as a water supply curve for a municipal water supply. It will have a static pressure(no flow condition), which is the greatest pressure and then show how much net pressure is created by the pump at various flows. As flow increases, pressure descrease for a centrifugal pump. Rememer a 500 gpm rated pump will have a range of flows, from 0 to greater than 500 gpm.
Then what you would do is simply add up pressure (pump net + hydrant pressure) at a number of different flows. (example water=500 gpm @ 50 psi, pump curve=500 gpm@150 psi. Combined water=500 gpm@200 psi. This gets a bit tricky with fire apparatus pumps because the RPMs can be changed, but it can be done.
This is where your pump discharge requirements are important.
What you really want to do here is to determine the flow and pressure you need from the discharge side of 500's. You would then take the hydrant water supply at that flow/pressure and then determine if there is an RPM on the fire pump that develops that same required flow and will have sufficient net pressure at that flow to boost the hydrant pressure to your required discharge pressure.
It's difficult to talk specifics without a lot of the necessary information, but I hope this is of help. In general, as I mentioned earlier, if the water system can deliver 1500-2000 gpm + flows for a hydrant, and you want to boost pressure at those flows, your 500's are going to come up short. If your expecations are less or the hydrant flows aren't that great, the 500's are a possible option. Hydrant pressures will also play a role, the greater the hydrant pressures, the more likely the 500's would be useful.
If you can wait, once the system is up an running, do some tests. Set up for a flow test off your 500's. Run your pump and if you can flow your required flow/pressure with a 20 psi+ residual remainig at the hydrant, the answer to your question is yes. If you can't get the required flow/pressure on the discharge side of your 500's, the answer is no.
08-12-2001, 10:45 PM #4
- Join Date
- Dec 1999
- Desoto County, MS
My mistake, cilfd is correct about the centrifugal pumps. My termonolgy was incorrect. Positive displacement pumps are what most of us are using for prime pumps. We I reread my post after read cilfd's post I could kick myself. I was thinking one thing and typing something else and didn't catch it when I reread it before posting. Sorry.Daron
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