# Tank gauges and water maker



## SanDiegoChip (Jun 12, 2007)

At present we have some sight gauges that were made up by the PO. They seem to work good and are fine for at the dock fill ups because it does not take long. They are located below our salon deck as is our engine. This requires us leaving open a large hatch. We would not like to leave this hatch open for long periods of time every other day if we needed to using a water maker. It is heavy and it is a safety issue. We have never used a water maker but will be installing one next year.

We are considering installing water tank gauges. Because the tanks are stainless steel and we do not have the room or say the desire to drill in from the top we are thinking of side sensor gauges. They are pricey. To install them requires we cut some plywood from the side of the tanks. At this time we are re-powering so w we have the engine out for the next month or so. Now would be the time to do this job.
My question is with a water maker do you need water gauges. 
We have two tanks with 55 gal in each one. So if say a water maker does 10 gal an hour would we realy need to worry about filling up the tanks if we ran it a couple hours every other day? Say we used more than that or keep track etc?
How does it work when you are using a water maker? Need to know how full the tank is or is there usually plenty of room?
Would we need to see the tank levels each time we make water or just check to see if the tanks have room?


----------



## JiffyLube (Jan 25, 2008)

I thought about that same issue too. I plan to use one tank at a time, isolating one tank as it's being filled by the watermaker. When one tank is filled I'll switch over to the other one, and fill that one while using the just filled tank. I'll be able to tell when the tanks are full when they over flow the vent, just like what happens when I fill the tanks at the dock. After awhile of living off the tanks I should be able to estimate usage, at least good enough to satisfy me.


----------



## Noelex (Jan 23, 2008)

Just a word of caution. I understand watermaker membranes do not like back pressure in their product water outlet.
If you wait until the tank is overflowing, if the overflow is above the watermaker you may be risking damage.
I have no idea if this is a significant risk, but I would be careful (or check with the manufacturer) until someone with better knowledge of watermakers advices its OK.


----------



## JiffyLube (Jan 25, 2008)

noelex77 said:


> Just a word of caution. I understand watermaker membranes do not like back pressure in their product water outlet.
> If you wait until the tank is overflowing, if the overflow is above the watermaker you may be risking damage.
> I have no idea if this is a significant risk, but I would be careful (or check with the manufacturer) until someone with better knowledge of watermakers advices its OK.


How much back pressure could there be filling up a vent line? I think once the vent line over flows I can switch the diverter valve for product water to the other tank, and shut the system down. Anyone see a problem with that?


----------



## Noelex (Jan 23, 2008)

JiffyLube said:


> How much back pressure could there be filling up a vent line? I think once the vent line over flows I can switch the diverter valve for product water to the other tank, and shut the system down. Anyone see a problem with that?


If I remember correctly every foot of water is about 2psi. Even if this rough rule is right it doesn't really help as I have no idea what back pressure in the product flow could lead to membrane damage, just that it can cause problems if "excessive"
I am sure with the vast knowledge of the forum someone will tell us the answer.


----------



## JiffyLube (Jan 25, 2008)

noelex77 said:


> If I remember correctly every foot of water is about 2psi. Even if this rough rule is right it doesn't really help as I have no idea what back pressure in the product flow could lead to membrane damage, just that it can cause problems if "excessive"
> I am sure with the vast knowledge of the forum someone will tell us the answer.


Is that 2psi for every foot of water going up a 1/4" or 1/2" vent line?


----------



## Noelex (Jan 23, 2008)

JiffyLube said:


> Is that 2psi for every foot of water going up a 1/4" or 1/2" vent line?


The pressure is not dependant on the size of the vent line only on the height of the water column above the membrane.


----------



## mitchbrown (Jan 21, 2009)

Hi Group

Its not 2 psi. .455 Psi will lift water one foot.

Mitch


----------



## Noelex (Jan 23, 2008)

mitchbrown said:


> Hi Group
> 
> Its not 2 psi. .455 Psi will lift water one foot.
> 
> Mitch


Thanks Mitch must have been 2 foot of water is about 1psi, not every 1 foot of water is about 2psi that I was trying to remember. Should have Googled it, but my internet from the boat is very slow at times.


----------



## CapnBilll (Sep 9, 2006)

You can put a sight tube anywhere before the pressure pump, it doesn't have to be attached to the tank. If the level is really important I would consider putting in a float switch. Then you can wire it to turn off the watermaker.


----------



## Tel321 (Jan 7, 2011)

The product tube should ideally be located at the top of your tank. At the bottom is a no no. But if you are close to the top there's not any real risk of back pressure doing any damage to the membrane. A suggestion is to have a three/way valve directly after the membrane to divert product water into a testing container or to fill jugs bottles etc. Switching this valve would easily resolve any back pressure issues. Be careful, some units are manual and some electronic and setting up a three/way valve will be a bit different for each.


----------



## Noelex (Jan 23, 2008)

Tel321 said:


> The product tube should ideally be located at the top of your tank. At the bottom is a no no. But if you are close to the top there's not any real risk of back pressure doing any damage to the membrane. A suggestion is to have a three/way valve directly after the membrane to divert product water into a testing container or to fill jugs bottles etc. Switching this valve would easily resolve any back pressure issues. Be careful, some units are manual and some electronic and setting up a three/way valve will be a bit different for each.


Thanks
Just to clarify if the product tube is at the top of the tank and the tank was overfilled, filling the deckpipe the watermaker should still be fine. Is this correct?
One less thing to watch if it is.


----------



## Tel321 (Jan 7, 2011)

noelex77 said:


> Thanks
> Just to clarify if the product tube is at the top of the tank and the tank was overfilled, filling the deckpipe the watermaker should still be fine. Is this correct?
> One less thing to watch if it is.


Yes you'll be fine. The reverse pressure on a water maker membranes is more of an academic issue than a real world problem. Many water makers are located well below the level of the boats water tanks and have no problems with reverse pressure. Remember, if you over fill your tanks they won't stay over filled for very long at all. As water makers go there will be enough to keep an eye out for, this issue is the least of them.


----------



## LakeSuperiorGeezer (Oct 8, 2010)

You could use water level electrode sensors going into the tanks using T connectors so you can keep the old sight tubes with electrode installation. The electrodes can trigger relays for automatic shutdown of the water maker.


----------



## Noelex (Jan 23, 2008)

Tel321 said:


> Yes you'll be fine. The reverse pressure on a water maker membranes is more of an academic issue than a real world problem. Many water makers are located well below the level of the boats water tanks and have no problems with reverse pressure. Remember, if you over fill your tanks they won't stay over filled for very long at all. As water makers go there will be enough to keep an eye out for, this issue is the least of them.


Thanks for the clarification.


----------

