DIY Watermaker

[s/v Jedi]

Originally Posted by thatboatguy

So Nick,

What do the instructions that came with your watermaker say about brackish water operation? Are you to scroll down pressure until you achieve design product output?

What make/model are you using.

George

I have an Offshore Marine Labs (same family as Village Marine). It is a very simple model, modular, with two 2.5 x 40 membranes and an AquaPro (also same family of brands) 3-plunger pump coupled to a 1.5hp AC motor.
The manual is not very exciting but I got a 2-hour private instruction from one of their engineers which was very good (negotiated that when I bought it)

With brackish water: if this is from river outflow, sediment is a concern. Only run the watermaker when the water, scoped up in a glass, looks clear without residue on the bottom if you let it stand for a couple of minutes.

I always start without pressure and the boost pump first. It'll push out most of the air that creeped into the system. After switching on the high pressure pump and waiting another minute or so, I slowly increase pressure until I reach rated output, catching product in a container. I look at both product- and reject-flow. If reject is less than 2 gpm there's something wrong. When the (1-gallon) container is half full, I direct product into a glass and smell and taste, before diverting product into the watertanks.

We get brackish water after a lot of rain. I can get rated output at 600-700 psi sometimes and run on that pressure. The total flow through the system is the same as with higher pressure. When I use fresh water as input, the pressure is so low that I get more flow at rated output.
The RO engineer stressed that adjusting for rated output instead of dialing in for 800 psi is the nest way and saves your membranes. Mine are well over 6 years old now and going strong, although salinity of the product has slowly increased to 300-400 ppm over the years.

cheers,
Nick.

[beau]

I am in the process of diy a RO watermaker, i have the membranes etc but I am having difficulty getting a pressure regulator here in Australia. Any suggested brands etc

[s/v Jedi]

Cat (pumps) sell them. The pdf linked in this thread also reveals sources.

cheers,
Nick.

[thatboatguy]

Originally Posted by s/v Jedi

The RO engineer stressed that adjusting for rated output instead of dialing in for 800 psi is the nest way and saves your membranes. Mine are well over 6 years old now and going strong, although salinity of the product has slowly increased to 300-400 ppm over the years.

cheers,
Nick.

Sounds good Nick, that's in line with what I've heard from other sources.

George

[dpex]

Originally Posted by Tellie

But back to your question, a new 40" membrane housing with end caps and gaskets can be had for about $250 and a new SW2540 membrane for about $250 as well. So unless you opt for two 40" membranes as I did the cost of them are about a 1/5 of the cost of the home built WM unit. The $64 question, how long do membranes last? A well taken care of membrane should last 5 to 8 years, perhaps more depending on too many variables to list here. The reality is that most are not well taken care of. To put it simply they are a pain in the arse to maintain properly as many here already know. If I were to build again I'd scrap the Cat pump and look for an E-Bay Sectra pump and build around it. Otherwise an entry level watermaker is not relly such a bad price after all.

Hi,

I'm curious about where you managed to source membranes and housings for such a low price. Here in NZ, Spectra want NZ$1500 just for the membrane.

Why would you scrap the CAT pump?

Cheers
Dpex.

[Tellie]

Originally Posted by dpex

Hi,

I'm curious about where you managed to source membranes and housings for such a low price. Here in NZ, Spectra want NZ$1500 just for the membrane.

Why would you scrap the CAT pump?

Cheers
Dpex.

Wow that's like $1,100 US. I don't know what Spectras prices are in NZ but that is way high compared to the states even for Spectra. I'll find out what the deal is and PM you the answers. The only reason for scraping the Cat is for it's energy requirements. A Clark pump is like the Holy Grail for a DIY watermaker builder. Spectra won't sell you one by itself and you just can't find used ones by themselves. Once in a Blue moon you might see one on E-Bay that has seen the better part of it's life used up. The two I have seen in the past three years where trashed by improper storage and could not be re-built. In fact I usually discourage even buying used plunger pumps for a DIY watermaker. More often than not the cost to buy them and then re-build them puts you very close to buying a new one. But if you go forward with building yout own and if you'd like give me a PM and I'll send you my E-mail address. I'd love to see what you have in mind and how you intend to go forward with your project. If I can lend a hand I'd be more than happy to.

[Brent Swain]

The General TT911 pumps work well, for under $300. Watermakers that put out too little take to long to make enough water to flush them properly, so they tend to not get flushed adequately.

[Leighton]

G'day

For anybody who's interested I have a water maker project for sale, one of those unfinished projects. The following are un-used and still in their original packaging.

Cat pump 2SF15SEEL triples plunger
Cat stainless steel pressure regulator
RO Membrane
RO pressure housing

Any offers??

Unfortuately shipping outside Oz would be probably uneconomical.


Cheers

Leighton

[akio.kanemoto]

Originally Posted by Leighton

G'day

For anybody who's interested I have a water maker project for sale, one of those unfinished projects. The following are un-used and still in their original packaging.

Cat pump 2SF15SEEL triples plunger
Cat stainless steel pressure regulator
RO Membrane
RO pressure housing

Any offers??

Unfortuately shipping outside Oz would be probably uneconomical.


Cheers

Leighton

Howdy,

What models/brands are the membranes and pressure housings? (I'm in Sydney)

Feel free to PM/email me (I can't PM you for some odd reason)..

[dpex]

Originally Posted by akio.kanemoto

Howdy,

What models/brands are the membranes and pressure housings? (I'm in Sydney)

Feel free to PM/email me (I can't PM you for some odd reason)..

Has the Cat pump got any pulley wheels on it? And what are you looking for, money-wise?

Cheers Dpex.

[Brent Swain]

Originally Posted by beau

I am in the process of diy a RO watermaker, i have the membranes etc but I am having difficulty getting a pressure regulator here in Australia. Any suggested brands etc

Pressure releif valves are available cheap from anyone selling pressure washers. Adjust them yourself. Change the plated bolt for a stainless one.

[reka30]

I read this thread (and many others in this forum on watermakers) with great interest. But, I have a question I can't find the answer to and am hopeful someone here might have it.

I want to install a watermaker. I would prefer to make approximately 40 gallons per hour, because of this I am not looking at a 12 Volt option. I will need to run the pump with an AC mother (I have a 6.5 KW genset) or belt-drive to the engine (which I really don't want to do).

The problem with an AC motor driven watermaker is the start-current on the AC motor. It seems I need to use 1.5 HP or a super-low start-up current 2 HP motor (if I can find one) to be able to start the motor.

I have looked at many watermakers, including ones mentioned in this thread and I must be missing something in the math.

I will use one manufacturer mentioned in this thread as an example:

-Same 2 HP motor (claims using 13.3 AC amps) drives a 30, 40, and 60 GPH watermaker.


I get that the 30 GPH has (1) 2.5 x 40 membrane, the 40 GPH has (2) membranes and the 60 GPH has (3) membranes.

What I don't get how the 2HP motor can push enough water to reach that claimed output.

Using the Cat Pumps talked about in this thread as an example:

3.6 GPM of seawater x 13% recovery rate = 0.468 GPM or 28.8 GPH
3.6 GPM * 800 PSI / 1460 = 1.97 HP motor (at 100% efficiency, which they aren't)

5.0 GPM of seawater x 13% recovery rate = 0.65 GPM or 39 GPH
5.0 GPM * 800 PSI / 1460 = 2.74 HP motor (at 100% efficiency, which they aren't)

7.7 GPM of seawater x 13% recovery rate = 1.001 GPM or 60 GPH
7.7 GPM * 800 PSI / 1460 = 4.21 HP motor (at 100% efficiency, which they aren't)


It seems that the 2 HP motor is capped out at approximately 30 GPH.

Clearly, I must be missing part of the equation on how we can use a 2 HP motor to get 40 or 60 GPH.

Or, as an early poster listed their 1.5 HP motor as driving a 40 GPH watermaker:

Originally Posted by s/v Jedi

Guys,

All the high tech of water makers is in the membrane. The rest is stupid simple. Of course a pressure washer works. It will work longer when all pump parts are stainless (not galvanized steel, not plastic etc.).

Once you have the pre-filters + boost pump + membranes + pressure valve + pressure meter + product flow meter + reject flow meter installed, you can experiment. What you need is a HP pump that can provide the needed pressure plus the needed gpm capacity. If you build from scratch, you need some rules of thumb. Let's take my 40 gph unit (which I use at 50 gph because that's what the membranes are rated for):

I use a 3-plunger HP pump coupled to a 1.5hp motor. With no pressure, the flow rate through the membranes -> reject is 4 gpm. With 45 gph product flow, the reject flow is 2 gpm, which is 120 gph. This relationship of 45:120 is roughly 1:3. So, for every gallon of product, you reject (at least) 3 gallons, or, in other words, 75% of intake water is used for cleaning the membranes. Remember that a membrane is a self cleaning cross-flow filter so you can go to 1:4 but not to 1:2. Just connect that pressure washer and slowly increase pressure and see what the meters tell you. When you reach 1:3 and the output is small, you need a bigger pressure washer or accept that smaller output.

I also shiver when people tell me they adjust for 800 psi pressure. That is wrong. You must adjust for the rated product-output of the membranes without going over a maximum pressure (800, 900, 1000 psi, whichever you feel is still safe, but not more).

The pressure needed for your rated output varies enormously. An example: for tropical (warm) salt water, you can reach max. product output at 700 psi, somtimes even less. If you put 800 psi on, you "overload" the membranes. In fresh water, the same unit will produce maximum output at 200 psi. If you go to 800 psi with fresh water, you will quickly ruin your membranes. In brackish water, you are anywhere in between. We are now on salt water but it's rainy season and after a lot of rain, I only need 600 psi pressure for full output.

You can also use a watermaker (a robust one) as your pressure washer with one extra valve after the HP pump (if you already have the fresh water flush valve, which all units have).

cheers,
Nick.

Is adding that 2nd and/or 3rd membrane really adding that much extra output without increasing the GPM the pump is putting into the membranes?

What is the effect of using the same CAT pump (for example) limited to 3.6 GPM with (1) membrane compared to (2) membranes compared to (3) membranes?

Thanks in advance for your answers!

[s/v Jedi]

Hi Reka,

The problem you are facing is that you are calculating for membranes that are connected in parallel. Our membranes are connected in series ,so the flow to the 2nd membrane is full pump output minus the product output of the first membrane. Roughly 66% or more of the pump output reaches the second membrane. This difference is exactly why that 2nd membrane always fails first.

Hope this helps,
Nick.

[reka30]

Nick,

Thanks so much for the reply. The information you have posted in this thread has been very helpful.

Can you dumb this down for me just a tiny bit more?

Are you saying that with a 3.6 GPM pump and with (2) membranes in series:

3.6 GPM will pass through Membrane #1 and roughly 2.4 GPM (66%) will pass through Membrane #2 at the same time?

Membrane GPM Recovery % Output GPM Output GPH
#1 3.6 13% 0.47 28.1 GPH
#2 2.4 13% 0.31 18.5 GPH
46.6 GPH TOTAL

Is that how you can get 40 GPH with a 2 HP pump?

If you use the same 2 HP motor and (3) membranes in series, do you get the same effect?

Membrane GPM Recovery % Output GPM Output GPH
#1 3.6 13% 0.47 28.1 GPH
#2 2.4 13% 0.31 18.5 GPH
#3 1.6 13% 0.20 12.2 GPH
58.8 GPH TOTAL

Is that how you get nearly 60 GPH with the same 2 HP pump?

Thanks in advance for some clarification!

[daddle]

[I don't know much about DIY watermakers, but not knowing never stops me from posting] If you need 2hp wouldn't it be better to use an engine or genset driven pump?