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.
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.
me with Questions: