Difference between marine watermarked and home reverse-osmosis systems

[ValiantV]

Hi all,

Rank newbie to this game, but have installed several home r/o (reverse osmosis) water purification systems with success, and wondering if a $200 home system could do the job of a much more expensive marine system - if only to a much lower capacity and even a shorter life.

Home systems (generally) operate on much lower pressures - typically 35-50 or so psi. I see some of these marine systems operate at 800 psi - which takes some doing to generate. Namely, an expensive pump and a good amount of power. Why this high pressure? Is it to greatly increase output, or is it a necessity when r/o-ing salt water?

I assume(!) that filtering salt water will require removal of a LOT more undesirable material from the pure water, but I'm fairly sure that upping the "wash" or "waste" water that carries impurities away from the membrane could easily be accomplished by increasing the office that controls this flow.

If course, the 3-stage "prefilters" ahead of the actual r/o stage will take more if a beating with a seawater input, but even so, these are relatively inexpensive and easily replaced.

From what I've seen, there are virtually no metal parts that cone in contact with the water, so corrosion shouldn't be an issue.

BTW, I have installed one home r/o unit that had a "boost pump" on it, but I doubt it upped the pressure to more than 100 psi.

Can anybody give some insight into this? I've not seen any in the forum so far, though it's possible I've missed it.

Thanks! (And be gentle!)

[meridian28]

In a home system you are just filtering fresh water. Saltwater systems need 800psi to push the fresh water through the membrane and

[Lepke]

I've been in boats and ships for a long time but knew nothing about RO. With some bad advise, I went where you're thinking of going. It doesn't work with salt water. I tried many things and modifications and gradually put together a system that works well. But I spent a lot.
You'd be better off to buy a component system that uses standard membranes and filters from someone like Cruise RO Water & Power: Watermakers for Boats & Yachts. It's still a couple grand but thousands cheaper than the yacht ready systems.

[JstaRebel]

Originally Posted by ValiantV

Hi all,

Rank newbie to this game, but have installed several home r/o (reverse osmosis) water purification systems with success, and wondering if a $200 home system could do the job of a much more expensive marine system - if only to a much lower capacity and even a shorter life.

Home systems (generally) operate on much lower pressures - typically 35-50 or so psi. I see some of these marine systems operate at 800 psi - which takes some doing to generate. Namely, an expensive pump and a good amount of power. Why this high pressure? Is it to greatly increase output, or is it a necessity when r/o-ing salt water?

I assume(!) that filtering salt water will require removal of a LOT more undesirable material from the pure water, but I'm fairly sure that upping the "wash" or "waste" water that carries impurities away from the membrane could easily be accomplished by increasing the office that controls this flow.

If course, the 3-stage "prefilters" ahead of the actual r/o stage will take more if a beating with a seawater input, but even so, these are relatively inexpensive and easily replaced.

From what I've seen, there are virtually no metal parts that cone in contact with the water, so corrosion shouldn't be an issue.

BTW, I have installed one home r/o unit that had a "boost pump" on it, but I doubt it upped the pressure to more than 100 psi.

Can anybody give some insight into this? I've not seen any in the forum so far, though it's possible I've missed it.

Thanks! (And be gentle!)

Yes, here is some insight. Look up Osmotic Pressure. below is the short version of the answer. Big difference between 250ppm (Tap Water) and 35,000 ppm (Seawater)

Osmosis is the diffusion of a fluid through a semipermeable membrane. ... The osmotic pressure of a solution is the pressure difference needed to stop the flow of solvent across a semipermeable membrane. The osmotic pressure of a solution is proportional to the molar concentration of the solute particles in solution.

[ValiantV]

Originally Posted by JstaRebel

Yes, here is some insight. Look up Osmotic Pressure. below is the short version of the answer. Big difference between 250ppm (Tap Water) and 35,000 ppm (Seawater)

Osmosis is the diffusion of a fluid through a semipermeable membrane. ... The osmotic pressure of a solution is the pressure difference needed to stop the flow of solvent across a semipermeable membrane. The osmotic pressure of a solution is proportional to the molar concentration of the solute particles in solution.

Ah. Now there's an answer I can understand!

Thanks, makes sense.

[ValiantV]

Originally Posted by Lepke

I've been in boats and ships for a long time but knew nothing about RO. With some bad advise, I went where you're thinking of going. It doesn't work with salt water. I tried many things and modifications and gradually put together a system that works well. But I spent a lot.
You'd be better off to buy a component system that uses standard membranes and filters from someone like Cruise RO Water & Power: Watermakers for Boats & Yachts. It's still a couple grand but thousands cheaper than the yacht ready systems.

Thanks for the link. Very helpful.

[Kita]

Originally Posted by JstaRebel

Yes, here is some insight. Look up Osmotic Pressure. below is the short version of the answer. Big difference between 250ppm (Tap Water) and 35,000 ppm (Seawater)

Osmosis is the diffusion of a fluid through a semipermeable membrane. ... The osmotic pressure of a solution is the pressure difference needed to stop the flow of solvent across a semipermeable membrane. The osmotic pressure of a solution is proportional to the molar concentration of the solute particles in solution.

I am not sure if I want to hug this guy or smack em! I almost hate to admit I actually understood that. But that sounded like Spock talking to Captain Kirk! That's a hell of a complicated way to say it takes more pressure to function properly with salt water because there's more material in it. I think a hug will work

[JstaRebel]

Originally Posted by Kita

I am not sure if I want to hug this guy or smack em! I almost hate to admit I actually understood that. But that sounded like Spock talking to Captain Kirk! That's a hell of a complicated way to say it takes more pressure to function properly with salt water because there's more material in it. I think a hug will work

Thank You for the hug. When you consider that I'm an engineer that designs, builds, and operates Desalination systems for entire islands throughout the Caribbean for a living, what you get from me is a professional reply when discussing SWRO.

[ValiantV]

Originally Posted by JstaRebel

Thank You for the hug. When you consider that I'm an engineer that designs, builds, and operates Desalination systems for entire islands throughout the Caribbean for a living, what you get from me is a professional reply when discussing SWRO.

Sometimes the Spock/Kirk reply is required to dispell the mere opinion and "I think" that often dominate a discussion.

That somebody actually has credentials actually helps too!

As a pilot and a mechanic, a technical description of a discipline I'm not well-versed on saves a lot of wasted time.

[Kita]

All in fun,really. It was a great answer & one I understand,well done....just kidding cause I worked with a bunch of engineers in machine shop and recognize the lingo, just thought it was funny it came across with so many big words and futuristic sound very cool really thanks....

[Crown Royal]

Some are for fresh water, some for sea, and some for inbetween (brackish)

[Jannie Radiance]

Go buy a Karcher Hi pressure machine. There is your hi pressure pump.Remove the pistons and have new ones turned out of 316 Stainless. You will need a supply pump.In South Africa we use 220v AC.I run mine from the inverter or small petrol ( gasoline) portable generator.Then proceed with the normal system. 20m filter and 5 micron filter and membrane etc etc.

[ValiantV]

Originally Posted by Jannie Radiance

Go buy a Karcher Hi pressure machine. There is your hi pressure pump.Remove the pistons and have new ones turned out of 316 Stainless. You will need a supply pump.In South Africa we use 220v AC.I run mine from the inverter or small petrol ( gasoline) portable generator.Then proceed with the normal system. 20m filter and 5 micron filter and membrane etc etc.

I think when we start talking about custom-machined parts - in stainless - we're well off into even more expensive territory.

I think by the time you get into buying fairly high-priced components like pressure washer pumps. (Even the "cheap" ones are prohibitively expensive to replace BTDT) you may as well spend somewhat more and have a system that is someone else's problem if something doesn't work.

[Jannie Radiance]

OK In SA a Schenker 35 Litres per hour unit cost about R70 000. I built one for less than 20k. Divide by 13 for USD price. I think yacht stuff is not so expensive in SA. My 32 square metre mainsail cost me USD 1600 in Dacron.3 reef points and 5 battens. How does that compare to US prices?

[SV THIRD DAY]

Originally Posted by Crown Royal

Some are for fresh water, some for sea, and some for inbetween (brackish)

Just to prevent a Cruise/Internet Rumor from being started, lets clarify this a bit.

A Sea Water RO unit CAN run in Fresh or brackish water as long as the water maker has the ability to dial down the system pressure. 800PSI is not needed in brackish or fresh water to reach the rated output of the unit, in fact taking the system to 800psi while operating in fresh water can damage the membrane.

Someone I know made a YouTube Video about this very issue...

https://www.youtube.com/watch?v=Ht2B3lpFbdQ