Originally Posted by beau
, I have puchased a petrol powered, brass pump pressure washer from ebay $400.00. A pressure gauge and regulator $150.00, 2 x Filmtec 2 X 2 1/2 x 40 inch membranes and fiberglass
housings $1,000.00. Just a bit of plumbing
and I am set to test it.
Under $2,000 and I should get 300 litres/hour
I hope you don't mind my .02 cents. It's meant with only good intent. Your post above sent off a few red flags
for me. I've seen this before in real world applications. My comments are made in general and are NOT
directed at you. These are just observations on the small post you made above that can be applied to others who want to take a DIY water maker project
on. Like others have said, it is not rocket science. But even a rocket scientist can get into costly mistakes
if he doesn't have enough information about things that are not rocket related.
Your figures are either a typo or a miscalculation. I'm guessing a typo but for fun let's say it's a miscalculation. If it were 30 liters per day (8gpd) or 300 liters per day (80gpd) the water maker would be very anemic and the two 2540s would foul in short order. If it is 300 liters per hour as posted (79 gph/1900gpd) it would be very impressive. For a short period of time. Filmtec 2540 membranes are rated for 700gpd production and 6gpm flow in perfect
conditions. Pushing them to 300 liters/hour would mean you would have to get 950gpd from each. The excessive pressures and flow needed to achieve that rate would send the membranes to an early demise. The pressures inside the membrane vessels would well exceed the 1000psi limits, pressures that many side walk cleaners can easily produce. Many vessels will not take these pressures and in time will burst. Also in your short list of materials you have left a few items out. What about a boost pump? You will certainly need one capable of delivering the volume of water a pump of the size needed to drive two 2540s will demand. Ceramic plungers will over heat in a matter of moments and will crack with a small amount cold sea water inrush. The energy used for the boost pump is a calculation that should be considered as well. You also don't mention the anticipated costs of good quality high pressure hoses and fittings. Will you use SS fittings attached to a brass pump? A $400 pump off of E-Bay, is this a new pump along with the gas motor
to drive it? Are you planning to run a gas engine below decks? Most people won't. If not how will you drive the pump? Engine take off or electric motor
. Those considering not using a gas motor below decks will need to consider the added costs of an electric motor
capable of handling a pumps demand to feed two 2540s and the associated electrical
needs. If it is an engine take off, what about a 12V clutch
? They're not $20 a pop either. What about a PTO pulley if either the engine does not have a spare available or you need an extra groove to drive a twin belt clutch
. What about an engine mounted bracket to bolt your pump to. A dedicated forward facing through hull
deep below the water line would be highly recommended for a water maker of this size. At least 3/4" in size, a 1" with a good ball valve would be preferable, if you have one unused on your boat great, many people don't. How large are your fresh water tanks
? Not only will you need to run your water maker a few hours at a time to keep the membranes healthy you'll need to take back enough fresh water made to give your water maker a fresh water flush after each use. Figure at least a five minute run with most water makers, probably more because you are using brass. Figure the flush flow at 6gpm. With a water maker of this size a boat should have fairly large holding capacities. Anything under 100 gallons and in my opinion this unit is too big for the boat. These are just a few things that people run into when building their own that they may not have anticipated. I never, never discourage anyone from this project
. But if anyone thinks that it is just a membrane, a high pressure pump and some plumbing fittings you really need to study a bit more first or chances are very good that you will be disappointed. Water makers, even home built ones are expensive. What is good for one is not going to be good for the next. Buying
or building the wrong one with too little information happens too often.