DIY Watermaker

[Rene]

I question putting the two membranes in series. Wouldn't the output from the first be pure fresh water. This becomes the input for the second. According to your oun info, fresh water input reduces the efficiency to a great degree. In parallel both could put out 100% and one could be isolated if it were to pack it in. You could still use the system in a reduced capacity. I'd hate to use precious and costly made water to wash my boat especially under very high pressure that can damage gelcoat.

[thatboatguy]

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.

Nicely worded Nick,

George

[thatboatguy]

Originally Posted by Rene

I question putting the two membranes in series.

I would characterize the plumbing arrangement of two pressure vessels as series/parallel. The output from both membranes is "pure" fresh water (hooked in parallel) while they are also both bypassing a large quantity of salt water in series. While the the input to the second vessel has a higher salt content than the first it's not significant. At least not in the size systems I've been building. As I update the series of photos on the Frankenmaker II I'll include some greater detail of the plumbing and I think it will become clear.

As for washing with fresh water... We are not wealthy people. We have our house, some realty investments and then the boat. It's a big asset for us and we wish to care for it properly. Our design goal and philosophy was to produce abundant fresh water as efficiently as possible. We also wanted a robust unit that was simple and field repairable. Space was of course also a big factor. The 48 HP main engine was simply not a good match for the power needs so we were left to choose between a generator running an electric motor running a hp pump, or a combustion engine powering the pump directly.

George

[s/v Jedi]

Originally Posted by Rene

I question putting the two membranes in series. Wouldn't the output from the first be pure fresh water. This becomes the input for the second. According to your oun info, fresh water input reduces the efficiency to a great degree. In parallel both could put out 100% and one could be isolated if it were to pack it in. You could still use the system in a reduced capacity. I'd hate to use precious and costly made water to wash my boat especially under very high pressure that can damage gelcoat.

Rene,

The connections between the two membranes are center to center (salt water) and outside to outside (product water). So, the raw water enters the center of the first membrane and part of it's H2O molecules gets "squeezed" through the membrane to the outside. At the other end, salt water (a little saltier than before) comes out of the center and gets fed into the center of the second membrane. The product water from the first membrane flows to the outside of the second membrane, mixes with the product water there and flows through to the system output.

I have been thinking about the product water plumbing for a long time and think I will change it so that both membranes have their own output-hose. This way, you can test the product of each membrane individually, before mixing it. Secondly, when membranes start failing, there's always one to go first, in which case it's output can be discarded while keeping the product of the good one. The membrane that fails first is always the same one, but I can't seem to remember if it's the first or second one (brain cells decaying...) My membranes are 6.5 years old now and still going strong but the ppm is higher and I want to know which one is causing that. But as all is within range, it's low on the project list right now ;-)

ciao!
Nick.

[scotte]

Originally Posted by s/v Jedi

I have been thinking about the product water plumbing for a long time and think I will change it so that both membranes have their own output-hose.

That's a really great idea! Better to be able to generate 1/2 the normal rate than 0... Though I guess you'd have to route the bad product water to discharge?

[JusDreaming]

here is the drawing I used

[Tellie]

Ok time to jump in here. Those who know me know what I do. They should also tell you I'll help you as much as I can. I know a little bit about watermakers. I read all the recent posts. Some good information some not so good, but close. Though it's not rocket science, it's not stupid simple either. You can try both methods but you'll either end up with an over engineered watermaker or a stupid one. I assure you neither will make you happy in the long run. You just can't grab any ol pressure washer pump off the shelf and expect it to work. Especially a $50 pump. Generating pressure cheaply is easy. Generating the proper pressure along with the proper flow is not done that cheap. It goes without saying that you have to have the right membranes for salt water. As you add multiple membranes your need for proper flow and pressure will require more from a pump. The science behind salt water membranes really doesn't change from manufacturer to manufacturer. Buying off the Internet membranes is fine to an extent. These are usually seconds and the lower producing membranes from the batch. But they should work. But make no mistake pressure regulation is extremely important. It is not hard at all with home made units to quickly over pressurize a membrane and ruin it in minutes. Not all plunger pumps are the same. The pressures, flow, and pump rpm are all over the spectrum. All which must be taken into account on an individual bases. Your buddies home built unit is not a one size fits all because it looks easy to copy on your boat. Your buddy may have a generator. You might not. Your pal may have a 1000 amp battery bank. You might have only 200amps. He might have a 120hp diesel. You might have a one lung beast at 12hp. Is your boat the same as his? Do you have the same space as he does? Does his bolt right on where his old compressor lived or do you have to build custom brackets? Does his have a calculated side load for engine driven pumps? These are not high amp alternators and engine bearings and replacement costs can outweigh any costs savings. Is the pump enough of an engine load or too light or too much? He might convince you he makes just enough water to take a shower once a week and that's enough for anyone to be happy, your wife disagrees. He may tell you I have 100 gallon tankage capacity on board and my creation makes 58gph. These are just but a few of the things I see and comments made all the time. If these comments don't send up red flags then you don't have a real understanding of watermakers yet. Again, I agree, it's not rocket science but it's not all that simple either. There is a learning curve with all watermakers that can get expensive real quick on that "I can build it cheaper than you can buy it for" watermaker. I understand there are some very talented guys out there that can do anything and my hats off to them. I'm sure we are all just like them. I've built several watermakers as well, engine PTO and electric motor drives and repaired plenty of others. Like any project you undertake on your boat you want as much information as possible. A simple set of plans make it look easy but there are a lot of other personal factors that need to be considered before deciding and undertaking a watermaker build.

[s/v Jedi]

Time for some corrections ;-)

1. The connections on the membrane are the other way around, ie. high pressure on the outside and product water in the center.

2. flow meter for brine/discard is 0-3 gpm. It measures about 1.3 GPM when I open the fresh water valves without any pumps running (other than the standard fresh water pump of course).

3. If you plumb a 3-way valve into the discharge hose for re-circulating you have an extra hose which I forgot to describe. It runs from this valve back to the input of the boostpump. So, there's a T on the boost pump input to accommodate the two hoses.

I think the rest is pretty correct ;-)

cheers,
Nick.

[JusDreaming]

Very well said Tellie, I built my own but would not build another for some one else. You are correct, if you build your own, keep your patience handy!! There are no DIY plans that can take in all the small details and nuances of each application. YOU need to be a bit of a plumber, part marine engineer, and part electrician/mechanic. And you better like to work upside down and under pressure (pun)!!
For an example, I got my pump all installed, system complete, and ready to start it up. Well then I read in the fine print on Cat pump web site, that you can not mount pump vertical!!! It was back to almost square one!!! New mounting bracket welded and designed, new belts, and re-routing hoses

[Tellie]

Originally Posted by s/v Jedi

Time for some corrections ;-)

1. The connections on the membrane are the other way around, ie. high pressure on the outside and product water in the center.

2. flow meter for brine/discard is 0-3 gpm. It measures about 1.3 GPM when I open the fresh water valves without any pumps running (other than the standard fresh water pump of course).

3. If you plumb a 3-way valve into the discharge hose for re-circulating you have an extra hose which I forgot to describe. It runs from this valve back to the input of the boostpump. So, there's a T on the boost pump input to accommodate the two hoses. Interesting Idea. Just a thought, if you plumbed it on the output side wouldn't you then actually be creating an energy recover type system? Plumbing it on the input it would seem to only accomplish reducing the amount of fresh sea water entering your system and increasing brine input. As you can't force more water past the boost pump than it will feed anyway. Just a thought.

I think the rest is pretty correct ;-)

cheers,
Nick.

I was going to let #1 slide

[thatboatguy]

Lots of good information here. I would personally stay away from "seconds" when purchasing membranes (personal choice). I purchase high quality membranes (Filmtec) from a reputable dealer -- American R/O. I also purchase pressure vessels from them. I have no interest in the company other than a satisfied customer. It's very true that all things have to be in balance for a watermaker to work properly over a period of time. I think a good approach is to decide how much water you want to produce, figure out your membrane arrangement to achieve that and spec the rest of the system out to meet the needs of the membranes. But I suppose you could take any of the major components and work the from them as well.

George

[s/v Jedi]

Tellie: I agree with you, pressure regulation is the tricky thing plus the components must be matched. But it isn't as difficult as it sounds, well, at least that's what I, being an engineer, thinks. I know much tougher problems to tackle. But I can also understand that this isn't easy at all for other cruisers.

JusDreaming: Your diagram is much clearer than my description. Interesting is that the membranes are plumbed in parallel in that diagram. It uses more high pressure fittings but obviously works as well. I think your setup is better than mine. I would improve it further with extra valves in each product water output line for testing or only using output from one membrane.

ThatBoatGuy: You are correct that good quality & 1st choice membranes is a better way to go. But it makes a lot of difference where you buy them. I mean, the membranes sold by your local water maker shop are available for much less elsewhere without resorting to 2nd choice etc. It's about the markup's etc. too.

In general: you will have to come up with some numbers of what you want, like how much product output you want and how to provide power. You can look at existing systems to get an idea of the possibilities.

For electric drive, the 1.5 hp 120/240V single-phase 1725 rpm motors seems popular. I have one from Baldor. These can directly drive a HP pump. If you look at http://www.catpumps.com/select/pdfs/231.pdf you will see that the stainless CAT231 pump matches to that. I have an Aqua Pro Titanium pump which is very simlar. CAT also sells the pressure regulators or versions for engine drive. The PDF linked even shows you how to calculate pulley sizes etc. Plus, you see the pump pressure range and flow rate. These numbers are usefull when you go looking at pressure washers. I have seen pressure washers with these same CAT pumps inside and the whole thing cost less than just the CAT pump (including gas engine!).

After that, you need to select membranes and the pressure vessels for them. The specs for the membranes will tell you exactly how much pressure, how much flow etc. As long as you keep the pressure lower than the maximum, and the product output flow lower than the membrane rating, and feed it properly filtered raw water, you can experiment without any trouble. A good match means that you get rated output with less pressure than the membrane's maximum and a crossflow (brine reject) of about 3 times more than the product flow.
There's the salinity of the water you're in to consider, plus it's temperature. My set is rated at 33 gph and the motor hp is the limiting factor (membranes can do 25 gph each. However, we are in the tropics with very warm water so I manage to make about 45 gph. With fresh water input, I can make 50 gph with only 200 psi pressure and the motor drawing very little.

I must say that I haven't seen any HP pumps for $50. Anyone knows that they aren't going to work, at least, not for long.

cheers,
Nick.

[beau]

The last time I got a quote for a cat pump here in Australia, I was quoted over USD$1,000, just for the pump.
I was thinking about a 240 volt quality pressure washer (Karcher) with a rating of 1600watts for $200 that I can use with my Kipor 2kva generator.
What do you think?

[thatboatguy]

There's an old saying. You can't take chicken poop and mayonnaise and make chicken salad.

But (and it's a big butt) in all fairness, what is the pump made of? What is it's design pressure and flow rate? What membranes were you proposing to use? The inexpensive pressure washer's available here in the states have parts mostly made of cast zinc commonly referred to as "pot metal". They would not hold up well to high pressure salt water.

The high pressure pump was the single most expensive item in the watermakers I've built.

Take a look at the Giant pumps. Stick with bronze or stainless (someone mentioned titanium!) for pump heads. Discuss your needs with a reputable distributor.

A long time ago, as a young man (OK a long, long, long time ago) I was pretty skilled at putting together nice sounding stereos. This was a popular skill to have among my buddies in the military. The most basic advice I could give anyone back then was to take half the money they had budgeted for a stereo system and spend it on speakers. This is another one of those kinds of deals.

George

[s/v Jedi]

Originally Posted by beau

The last time I got a quote for a cat pump here in Australia, I was quoted over USD$1,000, just for the pump.
I was thinking about a 240 volt quality pressure washer (Karcher) with a rating of 1600watts for $200 that I can use with my Kipor 2kva generator.
What do you think?

Beau: I agree with the others, what is the pressure and gph or gpm rating of that pressure washer? What is the pump made of? (you can see it when examining the unit closely)

I can tell you now that no $200 pressure washer is gonna do it and no 2kva generator (sounds like a gas unit) is gonna cope with the start-up surge. The pressure washer with CAT pump I described was $890.- or something and was gas powered.

cheers,
Nick.