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Old 13-01-2016, 14:50   #1
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water filter before or after pump

I have a small screen type filter before the pump and I just installed a Doulton Rio 2000 high flow filter after the pump. It works but it did reduce my pressure. Would placing it before the pump make any difference in water pressure?

Thanks!
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Old 13-01-2016, 15:34   #2
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Re: water filter before or after pump

The water filter should be after the pump. The problem is if the water filter is before the pump the suction head at the pump may be too high to operate. That is pumps push way better then they pull. So after the pump is how it should be done. Of course there is the pressure drop through the filter. You could install a pump with a higher head pressure.

In theory you could install a second pump after the filter, but that creates it's own set of headaches and it generally not recommended.
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Old 13-01-2016, 16:01   #3
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Re: water filter before or after pump

The filter should be BEFORE the pump, to protect the pump.
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Old 13-01-2016, 16:44   #4
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Re: water filter before or after pump

The "screen type filter" goes before the pump to protect the pump from solids in the tank. As SailorChic says your water filter is where it should be after the pump.


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Old 13-01-2016, 16:48   #5
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Re: water filter before or after pump

Lennie: You did it correctly. Stainer before the pump (to protect the pump), filter after (because the pump will cavitate if a restrictive filter is placed before the pump--all pumps have limited suction capability).

Perhaps some of this is about understanding terms. Although there is no hard and fast rule, strainers are generally >0.025" (50 mesh) and filters are generally micron-rated (the Rio is about 0.3 microns, or 0.000012").

You will get a little flow restriction, depending on starting pressure. You should still get 6-7 gpm at 30 psi when new, depending on the pump. If it is less than 2 gpm at an fixture, I would check the pump pressure.
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Old 13-01-2016, 16:53   #6
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Re: water filter before or after pump

Yes, I meant strainer before pump.
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Old 14-01-2016, 08:57   #7
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Re: water filter before or after pump

Quote:
Originally Posted by Terra Nova View Post
The filter should be BEFORE the pump, to protect the pump.
Absolutely. A decent pump costs bucks and there is no reason not to protect it!
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Old 14-01-2016, 09:31   #8
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Re: water filter before or after pump

Short answer is No, will make no difference. Resistance will be the same whether before or after the pump. Ideally both the pump and filter system should have the same resistance so they are not struggling with each other. Thus you probably did not match the impedance of the filter to your pump, did you?
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Old 14-01-2016, 09:55   #9
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Re: water filter before or after pump

True, but not nearly sufficient for the question. At sea level the absolute maximum suction pressure available is 14.7psia. The pump (any pump) has an NPSH (net positive suction head) requirement that has to be subtracted from that. Leaving, at very best about 10psia for all the losses on the suction side of the pump. Depends on the pump, a positive displacement pump (like a diaphragm pressure pump) may have a low NPSH requirement, a straight centrifugal pump generally has a high NPSH.

After your NPSH requirement you only have the remainder of your 14.7psia to lift the water to the pump inlet and pass it through the whatever strainer or filter you have on the suction side. The net result is you need very low losses on the suction side of the pump in order for the pump to even get water.

On the discharge side, however, you have available whatever pressure the pump can make, which is entirely dependent on pump design and available power. Normal water supply pumps might put out 30psig, and losing 5psi of that in a filter is no big deal. Lose the same 5psi on the suction side and the pump will likely cavitate and destroy itself.

Anything that might result in high head losses (a fine filter) belongs on the pressure side of the pump. Only items necessary for the protection of the pump (a coarse strainer) belong on the suction side.
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Old 14-01-2016, 10:04   #10
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Re: water filter before or after pump

OK it sounds like the filter is installed correctly. I have a Jabsco Par Max 3.5 25 psi pump and it's not providing enough flow for the shower.(wife is not amused) Any suggestions for a pump that will work well with my Doulton Rio 2000 filter?
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Old 14-01-2016, 10:05   #11
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Re: water filter before or after pump

On the discharge side, if the filter has a lower flow capacity that the pump, the pump will work against itself and probably self destruct eventually. Kind of like a pump trying to pump water into a blocked pipe. Kind of basic plumbing.
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Old 14-01-2016, 12:37   #12
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Re: water filter before or after pump

You could always put two of the same filters in parallel after the pump. This would reduce the effective pressure drop across the filters to half. Do you have the space?

If you stagger replace the filters then this can help even out the flows over time (i.e. not have very large flow after replacing both filters and have a really small flow right before they need to be replaced again). In this way when you put in a new filter it gets a larger amount of the flow, say 80%, which starts to even out a bit over time, but never below 50%. Then when you replace the other filter, this filter would see flows of less than 50% for the rest of its life.

Replace filters by monitoring the pressure drop (delta P) across them. Best of luck!
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Old 14-01-2016, 12:45   #13
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Re: water filter before or after pump

That filter is designed for residential water systems whose pressure, around here, is nearly 100 psi. Look at how low the flow is at 25 psi.

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Old 14-01-2016, 12:46   #14
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Re: water filter before or after pump

I went to the home improvement store and bought a "whole house" filter, figuring if you could run a whole house off of it, a boat ought to not tax it much.
Seems to have worked as I had tiny grains of lime coming off my old water tank and eventually clogging up the screens on my sink etc.
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Old 14-01-2016, 12:48   #15
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Re: water filter before or after pump

Quote:
Originally Posted by Terra Nova View Post
That filter is designed for residential water systems whose pressure, around here, is nearly 100 psi. Look at how low the flow is at 25 psi.

[IMG]http://doultonusa.com/doulton_water_filters/Rio2000-pressure-
chart.gif[/IMG]

But it is dead linear, indication if I read it correctly that the filter doesn't restrict flow? Of course flows goes up with pressure.
Residential water pressure is really 100 PSI? I didn't know that.
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