Water pump GPM, is it worth uping the GPM?? - SailNet Community
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post #1 of 16 Old 05-18-2009 Thread Starter
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Water pump GPM, is it worth uping the GPM??

The Islander Freeport water pump (original 1978) that comes with the boat we have is rated at 2.8 gal a min. That is for house water.
We are looking to replace ours as it is way too noisy.
We would like one as quiet as possible.
We also have a pressure tank.
There are a couple on the market we re looking at.
• I am wondering if we could up the gal a minute without busting water lines?
• Would there be an advantage to upping the gal per min?
• Would it make a nicer shower etc?
• The pump we have now seems to work fine enough
• Downside is we would use more water?
• We are also going to get a wash down pump so this will be used strictly for fresh water.

2.9 gal min
Jabsco 31600-0294 'Par Max 3' pressure-controlled pump
http://www.jabscosh op.com/marine/ p...lled- pump.htm

3.0 gal min
Aqua King™ Standard 3.0 (12 VDC) 3.0 GPM [11.35 LPM]
http://www.shurflo. com/pages/ Marin.../potable2 .htm

Thanks,
Chip
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post #2 of 16 Old 05-18-2009
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When they demo'ed the facilities here at the marina, I upped mine from a 3gpm to a 5gpm pump, I made sure all the lines were in good shape

So;
1. I haven't burst any lines yet ( almost a yr now )
2. that's a judgement call on your part
3. Yes, our shower kicks a$$ ( even has a massage head thing on it )
4. Again, a judgement call on your part
5. Yes, you probably will use more,

Downside is my our water heater is only 6 gals


Be sure to check the rating on your relief valve on your water heater to see how many psi it's rated for

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Last edited by poopdeckpappy; 05-18-2009 at 07:27 PM.
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post #3 of 16 Old 05-18-2009
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GPM = volume.
Lines burst from pressure--not volume.

So if the new pump puts out higher volume but the same pressure, there's no danger. Either the rest of the system can handle the extra volume, or it will choke it back. For instance, if you have a 1.5GPM shower heard--it will only pass 1.5GPM regardless of the pressure. But having a pump with higher volume might allow you to use the shower and galley at the same time without the water dribbling.

To some extent, hose diameters and fittings and the length of the hose runs will all limit the amount of volume the system will handle, and the capacity of your pressure tank will factor in as well. Bottom line is that you may see some improvement in flow, and there should be no risk as long as you're not going from 2.9GPM up to something like, say, 100GPM.
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post #4 of 16 Old 05-18-2009
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Small correction

Yes, lines do burst from the pressure. However if the line size remains the same the pressure must increase to deliver more volume. To put it another way, the line size causes the resistance to flow. To get more volume (gpm) the pressure must be increased to overcome the same resistance. It is very analogous to DC electric circuits: Voltage is the pressure, current is the volume, and resistance opposes the flow. You can push more flow thru the resistance by increasing the pressure.

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Originally Posted by hellosailor View Post
GPM = volume.
Lines burst from pressure--not volume.

So if the new pump puts out higher volume but the same pressure, there's no danger. Either the rest of the system can handle the extra volume, or it will choke it back. For instance, if you have a 1.5GPM shower heard--it will only pass 1.5GPM regardless of the pressure. But having a pump with higher volume might allow you to use the shower and galley at the same time without the water dribbling.

To some extent, hose diameters and fittings and the length of the hose runs will all limit the amount of volume the system will handle, and the capacity of your pressure tank will factor in as well. Bottom line is that you may see some improvement in flow, and there should be no risk as long as you're not going from 2.9GPM up to something like, say, 100GPM.

Gil
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post #5 of 16 Old 05-18-2009
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Usually, there is a switch on the water pump that turns off the flow of water when it reaches a certain pressure. Usually this switch is adjustable by you the owner, although it usually comes preset at a reasonable level from the factory. If your pump is rated for 2.5 gal per minute it is able to move 2.5 gallons of fluid in 60 seconds. It will do so until the pressure exerted by the fluid on the switch exceeds the level the switch has been set for.

Your pump will not burst your lines unless you set the switch to only turn off at a level that exceeds the capacity of the lines.

i.e. If your lines are rated to handle 75 PSI and you set your switch to 80 PSI, and there is no pressure relief (like an open tap) then your liines will burst.

If you do not set the pump switch higher than the rated capacity of your lines it will never pressurise your system past the level of safety, regardless of what volume it is capable of pumping.
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post #6 of 16 Old 05-19-2009 Thread Starter
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OK I am trying to find out the rated PSI capacity for the boat. It is not in the owners manual. Also I’ll look at the water heater for it’s capacity. Seems like we would like to go from the 3 gpm to the 5 gmp.
Along these lines the foot pump (Gusher Galley) is 3 gpm foot pump. We would like to put a water filter on it.
Has anyone had any experience with this?
Will it push water through a filter?
If so what filter do you use?

Poopdeckpappy,
When you upgraded to a 5 gpm pump which pump did you get and is it quiet?
Is there any noticeable difference in the noise level of the 3 gpm verses the 5 gpm?
Thanks
Chip
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post #7 of 16 Old 05-19-2009
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Hydraulics

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Originally Posted by hellosailor View Post
So if the new pump puts out higher volume but the same pressure, there's no danger. Either the rest of the system can handle the extra volume, or it will choke it back. For instance, if you have a 1.5GPM shower heard--it will only pass 1.5GPM regardless of the pressure. But having a pump with higher volume might allow you to use the shower and galley at the same time without the water dribbling.

To some extent, hose diameters and fittings and the length of the hose runs will all limit the amount of volume the system will handle, and the capacity of your pressure tank will factor in as well. Bottom line is that you may see some improvement in flow, and there should be no risk as long as you're not going from 2.9GPM up to something like, say, 100GPM.
Some pumping theory that might help. If you have a centrifugal pump (it has an impeller that spins) then the pump is capable of pumping a range of water pressure/volume combinations and each pump will usually have a published "pump curve" which illustrates these characteristics for that particular pump.

The piping system that receives the pumped water will increase its resistance as the pump tries to pump more water - this relationship is known as the "system head curve". With the right knowledge you can actually calculate the system head curve for a specific piping system and then plot this on the same graph as the pump head curve. Where the two graphs cross is known as the duty point and this point is the actual performance of that particular centrifugal pump/piping system combination.

On the other hand you could have a "positive displacement" type pump where the internal "slippage" of a centrifugal pump is almost totally eliminated. This type of pump will pump a more or less constant volume of water under most conditions. If the piping system is inadequate to handle this volume of water, then pressures will rapidly rise until you could get pressure induced breaks unless a pressure switch is installed.

Also unless the 1.5gpm shower head is fitted with a sophisticated pressure control system, the volume of water that it passes WILL vary with the pressure.

Lastly the referenced water system has a pressure tank. You will need to check to see how this is plumbed. If all the water from the pump has to pass through this tank, then nothing you do to change pump performance will have any impact on water pressures at the shower as this tank will control all downstream pressures. If the pumped water can reach the shower without going through this tank, then the selected pump will make a difference.

Confused?
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post #8 of 16 Old 05-19-2009
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SDChip, I went from a Jabsco PAR ( very noisey ) to a Shurflo with smart sensor, (very quite), also I went though WM who has a 2yr no question asked return/replace policy, you can actually take the pump back working or not and get a new one, each time extending the policy.

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I was with ya all the way until right after this point

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Some pumping theory that might help.

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If we installed the Shurflo 5.7 Extreme 65 psi Variable Speed Pump Controlled by Smart Sensor would you think we coud eliminate the presure tank?
Thanks
Chip
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