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Old 23-06-2016, 16:58   #1
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Watermaker Product flow pressure

can anyone tell me product water flow pressure, I'm try to figure out if I can T into freshwater tank outlet for watermaker output, which means it will have to be able to exceed head pressure from tanks to work I assume? Standard SW30 25-40 membrane at 800psi
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Old 23-06-2016, 17:13   #2
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Re: Watermaker Product flow pressure

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Originally Posted by Nauticatarcher View Post
can anyone tell me product water flow pressure, I'm try to figure out if I can T into freshwater tank outlet for watermaker output, which means it will have to be able to exceed head pressure from tanks to work I assume? Standard SW30 25-40 membrane at 800psi
Your post tells me that you will save money if you hire a pro. 800 psi is the pressure on the upstream side of the membrane. Pressure on the downstream side should be way lower but is not a set value. Flow is relatively independent of pressure there. Pressure will be whatever it needs to be to reach the atmosphere at whatever heightthat happens. Just a few psi will make tubing pop out.

Most water tanks in boats have pickups hanging from the top and work in suction.


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Old 23-06-2016, 17:23   #3
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Re: Watermaker Product flow pressure

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Most water tanks in boats have pickups hanging from the top and work in suction.
Agree. You should be able to tap into the tank delivery pipe with no issues other than: how are you going to direct the flow of water? If you're hoping to create flow to your taps (fawcets) without using your water pump, I reckon most of the WM product will probably just flow back to tank (line of least resistance?).
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Old 23-06-2016, 17:33   #4
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Re: Watermaker Product flow pressure

why not T into the vent hose?
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Old 23-06-2016, 18:39   #5
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Re: Watermaker Product flow pressure

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can anyone tell me product water flow pressure, I'm try to figure out if I can T into freshwater tank outlet for watermaker output, which means it will have to be able to exceed head pressure from tanks to work I assume? Standard SW30 25-40 membrane at 800psi
Maximum back pressure on permeate should
not exceed 50psi says Filmtec the manufacturer of your membrane. However, permeate back pressure on your system will effect flows, pressures, and conductivity. Best not to exceed 25 psi.
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Old 23-06-2016, 18:58   #6
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Re: Watermaker Product flow pressure

I believe Spectra will void the warranty if it is teed into the vent line.
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Old 23-06-2016, 19:35   #7
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Re: Watermaker Product flow pressure

From a hydraulic perspective, if you can T into the tank delivery line at a point above the top of the tank, there will be no head pressure, so no real worries. Do not T into the vent line, as if it fills with product, it could start a syphon and drain the tank.
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Old 23-06-2016, 19:41   #8
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Re: Watermaker Product flow pressure

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can anyone tell me product water flow pressure, I'm try to figure out if I can T into freshwater tank outlet for watermaker output, which means it will have to be able to exceed head pressure from tanks to work I assume? Standard SW30 25-40 membrane at 800psi

This is one of those instances I'd recommend simply doing this the right way. It might be a bit of a pain to do it but it is well worth doing it right. All watermaker product lines (The the lines that supply fresh water made from your system) should lead to the top of each tank, not the bottom or a manifold located below the fresh water tank/s. Splicing into the output side of your tanks feed (BEFORE the pressure pump of course) is usually considered a bad practice. There is more than enough pressure in the product line from the watermaker to overcome pretty much most head pressure created by routing the product line to the top of the tank on any boat without worry. In fact I usually recommend that the product tube from the watermaker be routed to underneath the galley sink. This way a simple two times 3/way valve set up can direct the product water to either tank individually or product water directly from the watermaker directed to the galley sink. This way if one or both of your tanks go sour you still have the ability to direct water from your watermaker directly to your galley sink thus eliminating the need to address the sour tanks right away. It would be tough to tell you the pressure of the product flow because so many different sized watermakers use a single SW2540 membrane and the flows and pressures are going to be different with each and that affects product pressure as well. But as sated above it is normally not much of a concern if the plumbing is done right.

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Old 23-06-2016, 23:14   #9
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Re: Watermaker Product flow pressure

A bit more research shows 1 psi = 27.73inches of head/water 68deg F, as my water tanks are probably only 2ft deep we are talking less than 1 psi back pressure if back preesure allowances quoted in #5 are correct feeding into bottom of tank should be well with in spec, infact if you think about it back pressure in line is exactly the same as taking it to top of tank if membrane out put is at tank bottom as volume of water in tank is immaterial, so I really can't see it being a problem and minimises plumbing run for my installation, sometimes I think we overthink things, anyway off to check Membrane back pressure specs.
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Old 24-06-2016, 00:07   #10
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Re: Watermaker Product flow pressure

The pressure required to reach the top of the tank will be no less than that required to overcome head pressure at the bottom. More, if the tank isn't full.


Think about it.
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Old 24-06-2016, 00:25   #11
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Re: Watermaker Product flow pressure

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The pressure required to reach the top of the tank will be no less than that required to overcome head pressure at the bottom. More, if the tank isn't full.


Think about it.
I agree, so shouldn't be a problem just to "T" into outlet.
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Old 24-06-2016, 03:31   #12
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Re: Watermaker Product flow pressure

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I agree, so shouldn't be a problem just to "T" into outlet.
Pressure wise should not be a problem but be mindful that pumping water back into the outlet at the bottom is going to stir up any sediment in the tank.
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Old 24-06-2016, 04:29   #13
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Re: Watermaker Product flow pressure

Again, route it to the top of the tank. It will say to do this in any reputable watermakers manual as well. First, tanks are not static. There can be quite a bit of hydraulic back pressure with a half full tank sloshing around in 3-4 foot seas. Second, tapping into the bottom of the tank is like adding another thru hull below the water line unnecessarily. Usually watermakers product lines are lighter use tubing not double clamped braided hose. Third, there is a reason water tanks in most newer boats today are all tapped from the top of the tank with the pick up going from the top to the bottom like a fuel tank.

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Old 24-06-2016, 05:30   #14
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Re: Watermaker Product flow pressure

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Originally Posted by Nauticatarcher View Post
I agree, so shouldn't be a problem just to "T" into outlet.
There are reasons for the manufacturer instructions that Tellie is kindly refering to.

For example:

If the pickup is blocked by debris then the tube between tank and freshwater pump will have negative pressure ie suction. If you do what are planning to do, then in that scenario the whole line from watermaker to tank will be in suction.

Anyone who knows a bit about potable water systems will tell you that risk of suction should be avoided to minimize risk of contamination.

Hence the recomendation of going to a dedicated fitting in the top of the tank, which is connnected to the air chamber in the tank, which in turn is connected to the atmosphere.

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Old 24-06-2016, 06:10   #15
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Re: Watermaker Product flow pressure

I think a few people here dont get the whole picture, my fresh water tanks are wing tanks, the fresh water pump feeds from the bottom of the tank, it T's off the balance pipe that between both tanks, there is already eight hose clips between tank outlets and freshwater pump a couple more will really make no difference, as tank outlets is already at bottom of tank sediment issue is not really a concern, water sloshing around in tank will not increase back presuure to any measurable amount as height of water will not go above tank height, watermaker outlet has a TDS controlled normally closed three way solenoid so in the event of any contamination it will close and isolate watermaker from FW tanks, back pressure is well within membrane spec's so I really cant see any reason why not too do this, just because most watermaker installations feed into the top of tanks is probably due to the fact that that is the easiest place to do it, any way I'm big enough and ugly enough to make my own decisions, thanks for all the advice.
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