Watermakers Pressure vs Output

[Lancerbye]

Village Marine Modular series for one. Others I have worked on which makes and models I can not remember. I know that they appear to be in series because often the HP input goes into the end of one membrane and is then taken from the other end to the next membrane. The other end returns to the backpressure regulator to control the pressure. If you examine this closely you will see that you have two paths in each membrane. HP to the out side ( at least in mine) and LP or product picked up from the middle. To increase product output you add more membranes (to a point) It would make no sense to have the product of one being fed to the next membrane. I know that filters are often run in series but each membrane is capable of producing product to spec on it's own.

[Dave852]

Originally Posted by Lancerbye

Village Marine Modular series for one. Others I have worked on which makes and models I can not remember. I know that they appear to be in series because often the HP input goes into the end of one membrane and is then taken from the other end to the next membrane. The other end returns to the backpressure regulator to control the pressure. If you examine this closely you will see that you have two paths in each membrane. HP to the out side ( at least in mine) and LP or product picked up from the middle. To increase product output you add more membranes (to a point) It would make no sense to have the product of one being fed to the next membrane. I know that filters are often run in series but each membrane is capable of producing product to spec on it's own.

That's in series because they are not talking about how the product water is plumbed.

[neworleansrich]

Some very good information in this thread.

Watching my flow meter lately in the Bahamas, I don't see too much difference between 700 and 800psi. I had been running below slightly below 800psi, but now will stick to 800 after reading all this.

By the way, I purchased a USED 20gph Cruise RO unit last year and this summer is the first I have it in operation. The guys at Cruise RO have been extremely helpful. There are many good RO units on the market, but the Cruise RO units are relatively easy to install since they use a good quality, color coded plastic flexible tubing along with snap-in fittings. This made the plumbing easy to do myself and made the finished job neat and professional looking.

A couple of things to consider no mater which brand watermaker you install: 1) Mount the pre-filters in a way that you can open them easily to clean or replace the cartridges (anticipating that you will spill some saltwater) My first location had them mounted above an AC water pump">raw water pump; not good. 2) Mount the membrane to something structural using some rubber. My first location for the membrane was attached to the underside of a cabin floor. When the unit was running the floor would resonate. 3) If you plan to carry a spare membrane, get a piece of 3inch PVC pipe and some PVC pipe caps. Glue one cap on the pipe, store the spare membrane in the pipe completely filled with pickling solution then cap the other end. Apparently, Dow's packaging is not sufficient for long term storage. (Rich at Cruise RO made this suggestion). 4) Carry spare impellers for the pre-pump. The Cruise RO units use a Commercial Duty Jabsco Water Puppy Pump. Personally, I have had much better luck with Shurflo pumps. They draw less and don't burn through impellers. Not a big deal, but maybe next year I will replace the Jabsco,

[phorvati]

Originally Posted by Lancerbye

They are in parallel usually.

After switching to engine drive in 2010, I ran 1 year with SW2540 in series, then the following year, I plumbed them in parallel. With engine drive you can increase the brine flow by increasing the RPMs. With AC Motor driving the pump, that's not so easy. I am much happier with them in parallel.

[Tellie]

As easily as you can reduce flow across the membrane you can easily flow too much, both to the detriment of your membranes. Make sure you achieve that balance.

[SV THIRD DAY]

Being a water maker manufacturer myself, here's the problem.
When I read incorrect information that can lead others astray on the understanding of how water makers (specifically RO Membranes) work, what do I do? Do I just stay out of it OR do I correct the chat room rumors and risk being looked at as a know-it-all-ass who won't shut up and always has to have the last word? Well I’ve been called worse, so I need to comment, besides I don't want to start my teak varnishing project for today...owning a Hudson Force 50 means you sleep a can of Cetol Natural Teak under your pillow!

Originally Posted by Lancerbye

I know that they appear to be in series because often the HP input goes into the end of one membrane and is then taken from the other end to the next membrane. The other end returns to the backpressure regulator to control the pressure. If you examine this closely you will see that you have two paths in each membrane. HP to the out side ( at least in mine) and LP or product picked up from the middle. To increase product output you add more membranes (to a point) It would make no sense to have the product of one being fed to the next membrane. I know that filters are often run in series but each membrane is capable of producing product to spec on it's own.

The membrane plumbing as described above by Lancerbye is indeed in series. The sea water just doesn’t pass through RO Membrane outer ports of the membrane housing, as he seemed to imply. But rather the sea water IS flowing through the RO Membrane and is now saltier sea water (brine) than want went into the membrane to start with. There is no sea water bypass in the RO Pressure Vessel or membrane. All of the water that flows into the Pressure Vessel on one end passes through the RO Membrane.

It also makes total sense to feed the high pressure sea water discharge (Brine) from pressure vessel No 1 into pressure vessel No 2. It's all about mainaining the needed flow rate through the membrane. In fact that is the norm and is done to keep the flow rate up to prevent membrane scaling and premature failure. You can't compare the function of a prefilter element plumbed in series for progressive filtration that passes 100% of the sea water through the filter element with a RO Membrane which doesn't pass the entire volume of sea water through the membrane element. As the sea water flows past the membrane surface (from one end of the membrane to the other) the reverse osmotic pressure (RO) that the 800PSI supplies pushes from 7% to 20% of the fresh water through the membrane surface. This is a common misunderstanding of how RO Membrane work and is why membrane get plugged up with scale and deposits if the sea water flow isn't ballanced for the membrane surface area. The No 2 problem with Do It Yourself water makers is not understanding the Hp sea water flow rate needed for a specific RO Membrane. I see it all the time when folks call me asking why their water maker isn't working.

Here are a few videos of how an RO Membrane works. Check out the 2nd and 3rd videos on the page. It helps to see the computer animation of how water flows "through" the mambrane element and how they are constructed.
http://www.cruiserowaterandpower.com...ker_Videos.php

Originally Posted by phorvati

After switching to engine drive in 2010, I ran 1 year with SW2540 in series, then the following year, I plumbed them in parallel. With engine drive you can increase the brine flow by increasing the RPMs. With AC Motor driving the pump, that's not so easy. I am much happier with them in parallel.

Engine driven or AC driven pump doesn’t really matter to the issue of membrane configuration. What you are looking for is the total flow rate matched to the RO Membrane surface area. Engine driven pumps typically have a higher flow rate than AC driven units, since powering the pump becomes less of an issue. It also isn't a good idea to try and varry your engine driven pumps flow rate with changes in RPM, in fact that is one of the big negatives on membrane life with engine driven water makers....so be careful. The higher flow rate can then give you the option of running in parallel since you have enough sea water flow rate to support the needs of each membrane even when it is divided in ½. However, the reality still holds true that the SW30-2540 membrane will have a longer life with 3.8GPM flow rate rather than 1.6GPM. It’s why plumbing the membranes in series is the industry standard way to do things to keep the flow to the membranes as high as possible.

[SV THIRD DAY]

Danm Cruising forum site with their lock out editing feature:
I talked about the positives of running the membranes in series…but what about the negative?

The negative is that membrane No 2 is processing saltier water (the brine) from the first membrane and since salt rejection is based on a percentage (99.4% for the SW30-2540) membrane No 2 in series will always have a higher TDS reading than membrane No 1. So the engineering balance is to figure out how much running the membranes in series will increase their life span vs the higher TDS being produced by membrane No 2. Your magic TDS number is 500ppm, so what gets you there faster (or slower) before the client needs to replace his membranes.

No more procrastination, time to go work on the teak.

[phorvati]

Originally Posted by SV THIRD DAY

Engine driven or AC driven pump doesn’t really matter to the issue of membrane configuration. What you are looking for is the total flow rate matched to the RO Membrane surface area. Engine driven pumps typically have a higher flow rate than AC driven units, since powering the pump becomes less of an issue. It also isn't a good idea to try and varry your engine driven pumps flow rate with changes in RPM, in fact that is one of the big negatives on membrane life with engine driven water makers....so be careful. The higher flow rate can then give you the option of running in parallel since you have enough sea water flow rate to support the needs of each membrane even when it is divided in ½. However, the reality still holds true that the SW30-2540 membrane will have a longer life with 3.8GPM flow rate rather than 1.6GPM. It’s why plumbing the membranes in series is the industry standard way to do things to keep the flow to the membranes as high as possible.

Not only higher, but you can control it via gas throttle. I only make water while in neutral. I keep the RPMs at whatever the value is to give me above 2GPM brine, and no pulsation. Then after every run, i take out the pre-filters and flush with about 5 gallons of product. For what is worth, another good thing is that i have not had a leak in high pressure lines downstream from the membranes in the past 4 years. Back when membranes were in series, I often had to change hoses, and fittings downstream from membranes. The only way to explain this is that brine is not as salty.