Question about short RO membrane

[zboss]

Guys,

I am pricing out the cost of making my own watermaker because I do not have the space necessary to install a 44" or dual 21" elements without significant modification to our boat.

I found these 14" elements and I was thinking of ganging 2 or 4 of them together but since I am just learning about desal I have a few questions:

1) Would just a single 14" element produce drinkable water?

2) I found a diagram of a home built system that had two elements together but I could not determine from the diagram if the elements get hooked in parallel or in series. Which is better? Pro's and Con's?

3) Suppose I wanted to gang together more than 4 elements? Maybe 8? How do I determine the size HP high pressure pump I need?

I also found these for the housing:

2.5" x 14" Fiberglass/FRP Seawater Pressure Vessel F2514-14141000C WaterAnywhere

Are these vessels appropriate for the intended use?

Also, I found these membranes that appear to only need much lower pressure, which means you could use a much lower pressure pump I suppose... why don't people use these membranes?

http://www.wateranywhere.com/product...products_id=61

Thanks...

- z

[sailormed]

Before asking a lot of questions have a look at the specifications of the products you indicate. I noticed after 1 second that the wateranywhere specification is set for "Performance specifications based on 2,000 mg/l sodium chloride...". Is this seawater?

[zboss]

Originally Posted by sailormed

Before asking a lot of questions have a look at the specifications of the products you indicate. I noticed after 1 second that the wateranywhere specification is set for "Performance specifications based on 2,000 mg/l sodium chloride...". Is this seawater?

Can't you gang them in a series?

[SV THIRD DAY]

Dual Membranes are almost always ran in series because you want to keep the sea water flow rate through them as high as possible. For example, a 1.6GPM Hp pump will have 1.6GPM going into Membrane No 1 and then roughly 1.3GPM going into Membrane No 2 when ran in series (0.3gpm will be gone as fresh product water when using a 40" membrane). Run these two membranes in parallel and each would see 0.8gpm...a lot less. More flow equals happier membranes and longer life as well as high fresh water production rates through the membrane.

There are 14" RO Membranes and pressure vessels...BUT....
I would stick with a more industry standard size like the 21" to make your ease and cost of replacement less and easier down the road.
As long as you are looking at a Sea Water membrane and not a brackish water or fresh water, then 40", 21" or 14" will all make good drinkable water. Remember shorter membranes will give you LESS water production for the SAME pressure and most importantly the SAME amount of Hp power and pump size! So why pay for the Hp power and then waste is on smaller membranes? Sure if you don't have room, then you don't but in my experience people always say they don't have room until they find out they will get 10GPH for the same price and power as 20GPH...then bingo...some room magically appears on the boat....

The membrane you list the link for is a low pressure membrane and is NOT A SEA WATER MEMBRANE...so no it will not work for sea water RO.

Yes the pressure vessel you link to will handle the needed 800PSI...no problem.

You can't just keep stringing together more membranes in series because you will have less and less sea water flow (and it will be saltier) in the down stream membranes and they will pug up fast. So there is a limit based on membrane surface area of your membranes and pump GPM.

How to size your Hp motor to your pump?
Maybe this will help...these are the numbers we use for the systems we build:
1/3 Hp needed for a 0.5gom pump
1/2hp needed for a 0.8gpm pump
1.0Hp needed for a 1.6GPM Pump
1.5Hp needed for a 2.3GPM Pump

Now how much fresh water will these different Hp/gpm pump combos make?

That depends on what membrane size we are talking about 14", 21" or 40" because fresh water production is a function of:
1) Membrane Surface Area
2) Sea Water Flow Rate
3) System Operating Pressure
Those things above you control...the things you can't control:
4) Sea Water TDS reading
5) Temperature of the water

Less Membrane surface area with the SAME Hp Pump and Motor will give you less water. So for the same power usage and cost you make less, which is why the 40" Membrane at $197 is the most efficient one to use....that is if you have space for it.

Look, do yourself a favor and download this manual as your starting point to help you figure out how to build your own and then ASK ME questions as they come up. I'm happy to help, no obligation to buy anything from me. There are so many damn BS rumors our there that you can really screw up and cost yourself more money than it would cost for an of the shelf system if you listen to the wrong advice.
www.cruiserowaterandpower.com/uploads/smsimple.pdf
This manual is the "simple" unit without the remote panel but it makes it easier to see what's going on and is a good template for a DIY-er.

Email me with Questions:
Rich@CruiseROwater.com

[zboss]

Originally Posted by SV THIRD DAY

Dual Membranes are almost always ran in series because you want to keep the sea water flow rate through them as high as possible. For example, a 1.6GPM Hp pump will have 1.6GPM going into Membrane No 1 and then roughly 1.3GPM going into Membrane No 2 when ran in series. Run these to membranes in parallel and each would see 0.8gpm...a lot less.

There are 14" RO Membranes and pressure vessels...BUT....
I would stick with a more industry standard size like the 21" to make your ease and cost of replacement less and easier down the road.
As long as you are looking at a Sea Water membrane and not a brackish water or fresh water, then 40", 21" or 14" will all make good drinkable water.

BUT the membrane you list as a low pressure membrane is NOT A SEA WATER MEMBRANE...so no it will not work for sea water RO.

Yes the pressure vessel you link to will handle the needed 800PSI...no problem.

You can not just keep stringing together more membranes in series because you will less and less sea water flow in the down stream membranes and they will pug up fast. So there is a limit based on membrane surface area and pump GPM.

How to size your Hp motor to your pump?
Here are the standard off the shelf numbers.
1/3 Hp needed for a 0.5gom pump
1/2hp needed for a 0.8gpm pump
1.0Hp needed for a 1.6GPM Pump
1.5Hp needed for a 2.3GPM Pump

Now how much water will these make?
That depends on what membrane size we are talking about 14", 21" or 40" because fresh water production is a function of:
1) Membrane Surface Area
2) Sea Water Flow Rate
3) System Operating Pressure
Those things above you control...the things you can't control:
4) Sea Water TDS reading
5) Temperature of the water

Look Download this manual as your starting point to help you figure out how to build your own and then ASK ME questions as they come up. There are so many damn BS rumors our there that you can really screw up and cost yourself more money than it would cost for an of the shelf system if you listen to the wrong advice.
http://www.cruiserowaterandpower.com...s/smsimple.pdf

Thanks Rich... will do.

I'm going to stick with 14" membranes even if they are more expensive. The replacement cost is secondary to the size. Although our boat is 38 feet LOA, we only have 29 at the water.

We literally have no where to put 21" membranes that would not take up crucial storage space that is already allocated to ships stores.

I did see that you did a custom design for someone that that needed to mount vertically on their engine room bulkhead - was that IN the engine room? I thought that was a no-no?

[SV THIRD DAY]

Another Myth...the "can't mount Membranes in an engine room".

I have my water maker mounted 12" away from my Ford Lehman 120Hp motor...and the membranes are now 8yrs old at 350ppm TDS.

What matters is two numbers:
1. That when running they are not allowed to be over 120-degs F. But remember, when cold water is running through them it's like a heat exchanger so it's darn hard to get the membranes hotter than 120 degs F.

2. When sitting unused the magic temps is 140-degs. That is a damn smoking hot engine room, but as long as they stay below 140-degs, they the membranes will be ok. Now 140-degs is hot...so I would be happier with 130-degs.

[zboss]

Originally Posted by SV THIRD DAY

Another Myth...the "can't mount Membranes in an engine room".

I have my water maker mounted 12" away from my Ford Lehman 120Hp motor...and the membranes are now 8yrs old at 350ppm TDS.

What matters is two numbers:
1. That when running they are not allowed to be over 120-degs F. But remember, when cold water is running through them it's like a heat exchanger so it's darn hard to get the membranes hotter than 120 degs F.

2. When sitting unused the magic temps is 140-degs. That is a damn smoking hot engine room, but as long as they stay below 140-degs, they the membranes will be ok. Now 140-degs is hot...so I would be happier with 130-degs.

Well, that changes things dramatically. You will warrant engine room installations then? Does your warranty require pro install?

[SV THIRD DAY]

As long as those temps are not exceeded....(120 for membrane in use and 140 for membrane in storage) we have no problem warrantying them...those are the temps straight from DOW Chemical, the makers of the membrane and from my own and other client experiences I'm confident you will be fine.

As for a "Pro Installer" that is YOU my friend...ha ha ha...
90-95% of our water makers are installed by the owner/user/cruiser that way they can save the typical $1500 to $2500 installation charges.

[Madehn]

Rich your answers and expertise freely given are much appreciated!!!!! dont mean to hijack the thread but in space concious boats like the OP's is there a limit on how much distance there can be between the hi pressure pump and the membranes? IE a limit on how long the high pressure hose can be?

[SV THIRD DAY]

Good question on Hp hose distance and one we get all the time because of the realities of installing a water maker on a space limited boat. The water maker has two Hp lines.
1. From the Hp Pump outlet to the Inlet of the RO Pressure Vessel
Then
2. From the RO Pressure Vessel outlet to the remote panel location

When we rated the water maker for power usage and fresh water production, we used TWO 30ft sticks of 3/8" Hp hose for these two line runs. And when we ran the system with shorter runs (our standard is 3ft and 5ft) we get the exact same fresh water production and power usage. Could you go longer than 30ft...I guess you could but then I say you are not really trying too hard to find a suitable mounting location honestly if a 30ft Hp hose run it too short for you!

Now before the engineers have a heart attach...sure there is some additional line loss in going from 3ft to 30ft...but SO WHAT? It's not measurable by the motor in terms of Amp usage at 800PSI and the fresh water production doesn't take a hit. So for what matters to us, it's a non-issue. NOW...we once used 1/4" line and YES we saw a difference there, which by the way is how/why we decided to upgrade both Hp hose runs to 3/8.

[zboss]

Rich,

When running through bulkheads what is the best way to protect the HP hose from chafe? Our boat basically uses hose glued in place but is there a better or more modern method?

[SV THIRD DAY]

Originally Posted by zboss

Rich,

When running through bulkheads what is the best way to protect the HP hose from chafe? Our boat basically uses hose glued in place but is there a better or more modern method?

I like to use a few inch pieces of the standard string reinforced water line, slice it open and then put it over the HP hose. Easy...simple...affective and cheap....what's not to love?

[Cheechako]

Wouldn't running membranes in series make for uneven pressures further along the line? IIRC my 120V 1.5HP system had 3 short membranes (21") in parallel...? BTW:It was in the engine room with no issues. Eventually I put one 40" membrane in due to maintenance of all the connecting fittings and end caps etc. I never really measured but there seemed to be little, if any, loss in output.

[SV THIRD DAY]

Sure but we're only talking 15 psi difference between the membrane. What is much more important is maintaining the highest flow rate possible through the membrane for proper scourging and long membrane life

[zboss]

Originally Posted by Cheechako

Wouldn't running membranes in series make for uneven pressures further along the line? IIRC my 120V 1.5HP system had 3 short membranes (21") in parallel...? BTW:It was in the engine room with no issues. Eventually I put one 40" membrane in due to maintenance of all the connecting fittings and end caps etc. I never really measured but there seemed to be little, if any, loss in output.

Yeah, learning that we could put the membrane unit in the engine room made a big difference. We would have had no way to mount a 40" membrane anywhere in our cabin except of forward locker and that would have taken up too much critical storage space.

Errrr. what do you mean "due to maintenance of all the connecting fittings and end caps"? What kind of maintenance do those components require? I was under the impression that maintenance normally meant pickling the membrane, swapping out the pre filters, flushing the membrane with RO water, and cleaning the filter basket.