Watermaker auto-TDS discharge idea

[plindheimer]

I'll be installing a 30 liter per hour watermaker this year and will install an inline TDS meter with the ability to trigger a relay upon a high TDS value. My setup will run the product water from the unit to a manual non-blocking diverter valve to test the product water or fill water bottles directly, and from there through a high loop and into one of two water tanks through another non-blocking diverter valve.

I'd like to take advantage of the TDS meter relay but it appears good quality non-blocking 3 way valves are very pricey. I have an idea and am wondering if anyone might have done anything like this or have some input based on your direct knowledge. I have no direct experience, this is all theoretical for me right now.

Keeping in mind this is a 30 liter per hour, so relatively low product water flow. My idea is to put the TDS probe shortly after the water maker and after that put a Tee in the line at a low level in the boat, probably about 1 meter below the top of the loop where the product water traverses to get into the tank. The other end of the Tee would go into a normally closed solenoid valve and from there into the bilge.

The idea here is, if the TDS meter detects high TDS, it will open the valve allowing the water to flow into the bilge, and since the path to the tanks rises 1 meter the path to the bilge will be favored. I will put a manual valve inline with the solenoid valve to be able to manually close this path and force the water through the normal path if needed. If the solenoid failed, since normally closed, it will allow the normal operation to continue.

Thoughts on this? Would some of the water still go to the tanks? Or has anyone come across a 3 way non-blocking diverter valve (12 v) that isn't really pricey?

Thanks for your feedback.

[stevenhigbee]

High TDS indicates a failing membrane. It gradually rises over its life. When it is discovered, the unit needs to be shut down until the unit is replaced. In the case of a membrane rupture, then it needs to be shut down until it is replaced, which is what the built-in sensor and relay seem to address. I don't see what you gain by diverting the water.

[plindheimer]

Originally Posted by stevenhigbee

High TDS indicates a failing membrane. It gradually rises over its life. When it is discovered, the unit needs to be shut down until the unit is replaced. In the case of a membrane rupture, then it needs to be shut down until it is replaced, which is what the built-in sensor and relay seem to address. I don't see what you gain by diverting the water.

As you point out, if there were a ruptured membrane, what you would gain by diverting the water to the bilge is not filling the tank with high TDS/contaminated water.

Btw this is something I would do for fun, as I always keep an eye on anything critical of which this would be one of them.

In any event, any feedback as to how such a setup would work is appreciated? Would the water still split and some of it flow into the tanks even with the ~1 m loop, other thoughts.

[SailingHarmonie]

Originally Posted by stevenhigbee

High TDS indicates a failing membrane. It gradually rises over its life. When it is discovered, the unit needs to be shut down until the unit is replaced. I've never heard of any commercial RO system having anything more than a meter reading during periodic maintenance. In the case of a membrane rupture, you'll likely notice your water getting salty before you check the TDS meter. There are other systems on your boat that would probably benefit from automated monitoring, long before this one.

Actually, many commercial systems have automated rejection of high tds product water.

The reason is that every RO system on startup produces poor quality water for several membrane volumes, and in a good system this water should be sent overboard, then once the water quality comes into spec, it can be sent into the tank. This is a more critical issue on water makers that run at high flow rates for short times, since they are in startup conditions for a larger fraction of their operation cycle.

[GreenWave]

My Sea Recovery Aqua Whisper has a built in meter for that startup period rejection.

[Tellie]

Instead of plumbing the high salinity discharge into your bilge just plumb "T" it into the brine discharge line. No muss no fuss.

[plindheimer]

Originally Posted by Tellie

Instead of plumbing the high salinity discharge into your bilge just plumb "T" it into the brine discharge line. No muss no fuss.

That's a possible option as well but it isn't relevant to my question, which is: With the high loop going to the tanks and the much easier path going to the bilge (or back into the brine line as you suggest) will all of the water at this low flow take the path of least resistance or will some of it continue into the tanks?

[cr180]

Originally Posted by plindheimer

I'll be installing a 30 liter per hour watermaker this year and will install an inline TDS meter with the ability to trigger a relay upon a high TDS value. My setup will run the product water from the unit to a manual non-blocking diverter valve to test the product water or fill water bottles directly, and from there through a high loop and into one of two water tanks through another non-blocking diverter valve.

I'd like to take advantage of the TDS meter relay but it appears good quality non-blocking 3 way valves are very pricey. I have an idea and am wondering if anyone might have done anything like this or have some input based on your direct knowledge. I have no direct experience, this is all theoretical for me right now.

Keeping in mind this is a 30 liter per hour, so relatively low product water flow. My idea is to put the TDS probe shortly after the water maker and after that put a Tee in the line at a low level in the boat, probably about 1 meter below the top of the loop where the product water traverses to get into the tank. The other end of the Tee would go into a normally closed solenoid valve and from there into the bilge.

The idea here is, if the TDS meter detects high TDS, it will open the valve allowing the water to flow into the bilge, and since the path to the tanks rises 1 meter the path to the bilge will be favored. I will put a manual valve inline with the solenoid valve to be able to manually close this path and force the water through the normal path if needed. If the solenoid failed, since normally closed, it will allow the normal operation to continue.

Thoughts on this? Would some of the water still go to the tanks? Or has anyone come across a 3 way non-blocking diverter valve (12 v) that isn't really pricey?

Thanks for your feedback.

Offering a different point of view. You don’t say whether you are installing a commercially available water maker or building yourself from components. Built my own from components using DuPont FilmTec membranes. All Manual control only with needle valve to control pressure. Start pump, let run for minute or so with needle valve open to flush, then slowly close to adjust to 800 psi. Potable water out routes through manual three way valve to either tank or to hose that fill water jugs or cup to manually test TDS. Don’t make water unless I can see the bottom, so clean sea water coming in. Said all of that to say, after 10 years of service, find consistent TDS readings each time use water maker. Yes they increase slowly over time as membranes age. So see no need for an automatic dump for increased TDS.

[plindheimer]

Originally Posted by cr180

. So see no need for an automatic dump for increased TDS.

Thanks, I am aware that I don't need that. This is 'for fun' ... I simply want to 'geek out' and understand how well this would work despite the fact that I will not be depending on it, I will manually check things on startup.

As far as what water maker, I'll be installing a Schenker Zen 30 -- 30 l/hr Clark Pump based low power unit.

[Tellie]

Originally Posted by plindheimer

That's a possible option as well but it isn't relevant to my question, which is: With the high loop going to the tanks and the much easier path going to the bilge (or back into the brine line as you suggest) will all of the water at this low flow take the path of least resistance or will some of it continue into the tanks?

It is relevant to your question. You are re-creating the watermaker wheel here. Water like electricity will take the path of least resistance to be sure, but your product water is under plenty of pressure to overcome any height on a normal boat so your "loop" is irrelevant. All initial product water on each startup of any automated watermaker should be directed to the brine discharge first. It is your solenoid that diverts your product water to the tanks when it gets its signal from your TDS meter that the product water is of sufficient quality. If your installed TDS meter detects high salinity in the product water your diversion valve should send this high TDS product water back into the brine discharge line so it's routed overboard and NOT into your bilge. Thus, none of the high TDS product water will flow to your tank until your TDS meter says so.

[plindheimer]

Thanks for your further feedback and yes your feedback is relevant to the overall concept even though I am mostly wondering if my 'fun' project would work since I'll still use my own manual valves to make sure the water is ok before sending to the tank.

But your response here did specifically address my question in hand:

Originally Posted by Tellie

...your product water is under plenty of pressure to overcome any height on a normal boat so your "loop" is irrelevant.

After thinking about this for some time, it occurred to me that many people 'Tee' into their tank vent line to fill the tank, in fact it is specifically mentioned that this is ok in the manual. If there was so much pressure, then you would think some of that product water would end up going up the vent loop and out the end of the tank vent but that does not seem to be the case. Given this, it seem like, at least with proper hose diameter changes at the Tee, if you had it open to the bilge it would all flow there as this would be similar to going to the tank. Reconnecting into the Brine line may not have the same affect as there may be a lot of back pressure coming from that water flow unless you vented into a much larger diameter hose at the end of the Brine line before going overboard where the pressure issue would no longer be a problem.

[BjarneK]

I have a 24 L/min watermaker and the route from the membrane to the tank is fairly long and a bit restricted by a thin access tube to the fresh water tank. The watermaker is located about 90 cm above the tank, so that would create a negative contribution to the pressure, basically "sucking" the water toward the tank. With that setup, the outgoing pressure from the membrane is about 60 mbar, so around 60 cm head of water.

So with a relatively short connection to the water tank using a good diameter hose without too significant restrictions, I would think your idea could work.

[plindheimer]

Thanks for your info,

I'm on the road to find out as I'm in the process of installing my water maker. Since my watermaker has an auto-flush ability what I did was to purchase a spare solenoid valve that is used on the auto flush providing a spare in case of failure.

I will use this spare for my setup along with an inline ball valve, so in the event that I had to use it I can just close that circuit.

I just got some 1/4" internal diameter hose to attach to the output of that valve that will run to the bilge. The product water line then runs through a 1/4" outer diameter hose (I think those are 0.17" internal, so 1/2 the volume) quite a bit further, up through a swan neck that will raise at least 1 meter before dipping back down and into a series of 3 way valves. One for testing product water or filling bottles/jerry cans directly and then a tank selector. Given all that I fully expect when the valve is opened, all the product water will flow to the bilge. If not, I'll bump up the exit tube size. (The valve itself is 3/4" NPT).