watermaker plumbing debate-gctid347356

[ksanders]

The question is:

The output of our watermaker needs to be plumbed into the freshwater tank.

The easiest place to plumb it would be to a tee on the suction side of the potable water pump.

A more difficult place would be to a tee in the tank fill line.

The debate is/was where is the best place to plumb it into.

One thought is that it would be easier for the watermaker to push the water in a hose to the top of the tank and tee into the fill

rather than pushing against the weight of the water in the tank.

But on second thought I'm not so sure of that. Wouldn't the pressure be based on the height of the water colum, not the volume of the tank?

BTW the instruction manual is unclear about this.

Thanks

[Guest]

Hello there is not much difference here. In the tank fill scenario you still have to face the small but real head to go from the pump up to the tank fill. In the other you will face the static pressure in head from the center of the pump discharge, to the height of water level the tank is at. (plus a tiny bit of friction pumping back to the tank in 1/2" line) I would put it wherever the distance is shortest. Static Head faced by the pump is the same in either. Dynamic head is lower the shorter the line you use.

Cheers steve

[Guest]

Kevin I had the same debate when we installed my RO unit. I understood that static head was the same but opted to run to the top of the tank. My reasoning, I would rather push the mass of water to atmosphere, i.e. top of tank than to the bottom of the tank with a mass increasing to 60 or 140 gal. I checked with one of my engineer buds and her agreed. Routing was a challenge but doable. Good luck.

[Guest]

When I ask this question to several mfg's they all said above the water tank. Fill line prefered. Water pick up is more of a problem for me. they said mid ship CL

[Guest]

Routing water to your two tanks is going to mean running one or two lines from the water maker up to the fore peak to tie into your fill lines for your tank. You will have considerable distance to run your supply lines. It probably will not be too difficult up the port side under the bunks. You will have a little more dynamic loss feeding to the top of the tanks but not a lot considering the length of your lines from the tanks to the supply pump or selector valve will be only slightly shorter than your new lines to the tank fills. Static head is static head. If you fill near water pump or selector valve it varies with the water level in the tanks if you pump to the top of the tanks it's always the same. If you fill to the tops of the tanks you will have to run two lines as both tanks are separate systems to the selector valve in the pit. They are also at different levels and do not connect to each other except at the selector valve. You can only draw from one at a time on my boat. Yours may be different as to drawing off both at once but mine isn't able to. It makes sense to me to tie in just in front of the selector valve in the pit as it's not only a lot easier location but simpler without drawbacks as I see it. It will also let you manage which tanks is being filled from a convenient location. Keep it simple.

[The_Other_Gary]

As long as the output of the watermaker is higher than the water level in the tank the laws of physics prevail.

Piping to the top or bottom has no bearing on the direction or volume of water flow.

The only time when water will not flow is when the tank is full and the level equals the level in the vent tube and only

if the vent tube outlet is higher than the water maker output.

[dmcb]

Thought of the day. If you have a watermaker, do you need two water tanks?

Doug

[ksanders]

This is an interesting discussion

I tend to agree with Scary in that the tee would be much easier after the tank selection valves on the suction side of the pump, for all the reasons he mentioned.

My installer whom I have trusted with many other projects and who has never let me down, agrees with Billsguns and is more comfortable with the tee in the fill line to the large tank.

If I were doing the job myself I would tie it in down in the engine room and be done with it.

Since I've hired this job out I'm going to go with NHD's experienced recomendations. Throughout this project I've given NHD broad lattitude to accomplish the jobs I needed done. They've always done an excellent job and I expect this one will be the same.

On the issue of needing a second tank, and moving water...

We'll have to see how that one plays out in actual use. I'll probably end up not using the lower tank much, but that will lead to bacteria problems. Then again if I open both tank valves the upper large tank will gravity fill the lower tank. If I cycle between both tanks, then it might be better. We'll just have to see.

Another thought is if I normally run off of the lower tank, and fill the lower tank from the upper tank, I can then test the water going into the upper tank both before and after a watermaking cycle. This would give me a buffer of known good water in case there's a watermaker malfunction.

[RDOIII]

The answer regarding relative head pressure is that it will be higher to go to the top of the tank.

The easiest way to visualize is to think of the column of water from the hose extending into the tank - it needs to go only to the surface of the water in the tank. A hose to the top has a column of water as high as the top of the hose before it turns down into the tank. But in reality one foot of difference in head height is only about 0.5 psi.

RDO