Water Maker Flow Rate Too High?

[Tday01]

Our Sea Recovery water maker was making 50% more than its rated capacity of 33gph and the water was perfectly acceptable. I presume that this is because of high temperature and low salinity.


Sea Recovery told us that we had should turn the pressure down until we were getting 33gph or membrane life would be decreased. Does anyone know why this would be true, and whether shorter life would be in terms time or total water produced during the life of the membranes?

[s/v Jedi]

Originally Posted by Tday01

Our Sea Recovery water maker was making 50% more than its rated capacity of 33gph and the water was perfectly acceptable. I presume that this is because of high temperature and low salinity.


Sea Recovery told us that we had should turn the pressure down until we were getting 33gph or membrane life would be decreased. Does anyone know why this would be true, and whether shorter life would be in terms time or total water produced during the life of the membranes?

33 gph? what a strange value? I thought it was 20 or 40 gph...

Anyway, they are right that you should adjust pressure for rated product capacity. However, insiders have assured me that my membranes would not be hurt when I bring my 40 gph system up to 50 gph as long as pressure stays under 800psi. Like you say, high water temperature and/or brackish water make that difference. I only need 200 psi for 50 gph when I feed it fresh water.

My 2003 membranes (10 years!) have outlasted my pressure vessels that have begun to leak...

cheers,
Nick.

[Tellie]

There are several variables that effect production. Temperature and salinity are two big factors but 50% more production is a lot. Are you in fresh water? I agree with Sea Recovery and Jedi. Your system can make more product safely in certain conditions to a point. RO requires a balance between pressure and flow. Too much or too little of either can damage membranes. Watermakers that don't self adjust for changing water conditions, usually those with manual needle settings, have been known to damage membranes when going from salt water to fresh. If your system is the 750 then it's rated for 31gph. Without knowing what water you are in I wouldn't state what you should definitely do. But with the information you do provide I would probably back down the pressure to reflect a closer to normal production. If you're making 50% more product and your TDS readings are the same or lower than normal you are perhaps flowing too much water too fast over the membranes. A flow test is the only sure way to know.

[Tday01]

At the time I was in the Caribbean with 84 F water. Backing pressure down to 550 gave normal production.

[Tellie]

Originally Posted by Tday01

At the time I was in the Caribbean with 84 F water. Backing pressure down to 550 gave normal production.

You said that it made perfectly acceptable water. That may be relative. What were the TDS readings when you made 50% more and what are they now since you've scaled down the pressure to make the rated product water?

[Tday01]

300ppm at high flow rate, 200ppm at lower flow rate. The watermaker won't pass the water through unless it meets a certain standard (which I don't remember).

[Tellie]

Originally Posted by Tday01

300ppm at high flow rate, 200ppm at lower flow rate. The watermaker won't pass the water through unless it meets a certain standard (which I don't remember).

Hmmm I half expected higher TDS readings. At this point I would say that perhaps you weren't making up to 50% more unless you did a measured product flow test to confirm it. Usually that kind of extra production would be a definite sign of membrane damage and your TDS readings don't jive with that type of damage which is good. But I would certainly look more to the rated product output and use those parameters as how to adjust your system. If yours is rated at 33gph it is either a 750 or 800. People sometimes in an effort to make more water crank the pressure up. It will make more water under higher pressure but it will also cause a problem known as compaction and shorten the membranes life. Keeping your system at it's rated output will ensure the proper flow to pressure ratio as designed. Sea Recovery will tell you that all membranes are not created equal and they are correct. Their systems are designed to work best with their membranes and their parameters are set through hard won experience.

[gbanker]

Telle,
Probably "jumping" this thread, and moderator you can move my post if necessary. Regards membranes- I have heard that the membranes sold by watermaker companies are the same, but much more costly, than those supplied to othes such as photo shop/film companies. Would you like to comment?

[Tday01]

gbanker see this thread

http://www.cruisersforum.com/forums/...ane-33794.html

[gbanker]

thanks

[Tellie]

Originally Posted by gbanker

Telle,
Probably "jumping" this thread, and moderator you can move my post if necessary. Regards membranes- I have heard that the membranes sold by watermaker companies are the same, but much more costly, than those supplied to othes such as photo shop/film companies. Would you like to comment?

No problem. SR and VM membranes are proprietary and their systems are based on the differences in flows and pressures they want. Many systems membranes are not proprietary and can be interchangeable. Converting to a non proprietary membrane usually requires adjusting the systems pressures and flows because they are set up for the requirements that are built into proprietary ones. Every system will be different based on the size of the unit. I know it's easy to assume it's always about charging more to the end user for profit but they are trying in the very small boating area of the RO world to come up with better quality membranes that provide not only better quality/quantity of water but will last longer and be a bit more robust and forgiving of what the average user puts them through. I believe a lot of their R&D into membranes is focused on bigger things and the boating market is just a small portion of their concerns. I don't deal with photo shop/film companies, I can barely get my cell phone to take a picture, so I don't have any first hand knowledge or dealings with photo shops. I think that it was the needs in photo shops and printing shops that the SW membranes were developed for originally. I wish I was the first guy that said "Hey, I can use these on boats".