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Old 02-05-2007, 08:27   #1
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Watermaker Pressure Vessel

Does anyone have any experience with building a pressure vessel for a watermaker or would I be better of buying an off the shelf model?

Thanks for any advise.
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Old 02-05-2007, 16:43   #2
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Dan,

I suggest you purchase the vessels from a vendor due to the fact that they are high pressure vessels (700 - 900 psi) and somewhat dangerous.

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Old 02-05-2007, 23:20   #3
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so the frp wrap here is not a pressure vessel and this needs to have one made
SWC-2540 Hydranautics 2.5' x 40' Sea Water Membrane
sean
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Old 03-05-2007, 01:13   #4
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Exactly ...
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Old 03-05-2007, 03:11   #5
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can you use schedule ss pipe and just weld caps on the end to which you drill and tap for pressure hose or do these need to be specially made
sean
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Old 05-05-2007, 09:34   #6
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It's not that simple. The end caps need to be removable and be machined to fit the membrane. Do yourself a favor and get a commercially made pressure vessel.

Bob Stewart
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Old 05-05-2007, 12:03   #7
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If you make a pressure vessel, you need to have it hydraulicaly tested to at least 3 x it's working pressure. This is not something you want to muck around with. If the thing ruptured violently, you may have a new porthole placed in your boat and with Murphy's laws, it has a good chance of being an underwater viewing port.
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Old 03-07-2007, 08:58   #8
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Quote:
Originally Posted by Alan Wheeler
If you make a pressure vessel, you need to have it hydraulicaly tested to at least 3 x it's working pressure. This is not something you want to muck around with. If the thing ruptured violently, you may have a new porthole placed in your boat and with Murphy's laws, it has a good chance of being an underwater viewing port.
-----

This is not factualy true Alan , we are talking about waterpressure , when you get a rupture into a tank filled with water , you get a simple .....splash.
No big deal.
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Old 03-07-2007, 09:33   #9
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Bobs, the pressure vessel of a watermaker is out in the open with 800 psi inside, and the most common HP pumps can put out 2-3000 psi if the discharge is closed. Cpt Dan, buy your pressure vessel and membrane as an assembly. Unless you work for minimum wage, you'll save money. In fact, I would recommend you buy the complete system in a fully modular configuration - that's all the discrete components and you mount, plumb and wire them yourself.

When installing a watermaker you want to run the product output line all the way to the top of the water tank. If you must tap it into the existing water supply line, as is frequently done, you MUST install both a spring-loaded ball or cone check valve AND a carbon filter in the line. Otherwise, chlorine from dock water in the tank will migrate through the water path and kill the membrane over time. You should include in your installation 3-way valves in the seawater suction and brine discharge lines for cleaning and preserving, and another in the suction for flushing the unit with fresh water AFTER EACH USE (not necessary with DAILY use). The flush line must have a carbon filter to remove chlorine, and that filter element must be replaced when about 200 gallons of dock water has run through it - about 30 flushes more or less. The used elements can be rejuvenated by placing in a warm oven for a while, or simply airing out.

Yes, I sell them. It's not the purpose of this reply, but if you need a source, email me at: tech@midatlanticseatech.com
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Old 03-07-2007, 09:45   #10
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EngNate, a pity your site is still under construction.
I need a membrane , including a vessel dough.

Greetz
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Old 03-07-2007, 10:09   #11
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The site is still off on the horizon, but we are the Mid Atlantic distribution and support center for Village Marine Tec.

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Old 03-07-2007, 11:15   #12
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bobs:
Two consequences resulting from a sudden & complete rupture of a pressure vessel, which could apply to water-containing vessels:
1. Blast effects due to sudden expansion of the pressurized fluid.
2. Fragmentation damage and injury, if vessel rupture occurs.

It’s only a leakage failure, wherein the hazard consequences can range from no deleterious effect for water vessels, to very serious effects such as:
1.Suffocation or poisoning, depending on the nature of the contained fluid, if the leakage occurs into a closed space.
2. Fire and explosion (physical hazards for a flammable fluid).
3. Chemical and thermal burns from contact with process liquids.
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Old 03-07-2007, 21:29   #13
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Gord,

Gord, in this case I am afraid you're wrong. Or to be more specific, what you quoted is technically correct, but does not practially apply in this case.

If the pressure vessel is full of room temperature water there is NO expansion of the pressurized fluid (for all practical purposes). Because water is so incompressable even at very high pressures, there is very little engery stored in it. Failures of vessels containing only water are not very dramatic. You can see the details of the calculations here:

Calculation of Potential Energy Stored in Compressed Water.

If the vessel was full of gas it is a very different story.

One practical lesson from this is the use of plastic water pipes. If they fail under 100 psi of water pressure, the split open and the water pours out. If the fail under 100 psi of AIR pressure, they send plastic shrapnel flying through the air.

I knew my parents sent me to engineering school for a reason.

While it is true that a water containing vessel is not dangerous at high pressures, the design of a 2000 psi vessel that is expected to remain leak tight while enduring long term exposure to something as corrosive as seawater is not an exercise for the garage mechanic.

Bill
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Old 03-07-2007, 22:00   #14
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I built my own pressure vessel . Works well.Standard 540 gallon a day membranes fit perfectly in a standard 2 1/2 inch sch 40 stainless pipe. The end caps are held on by two half inch stainless bolts per end . My book tells you how to build the ends etc . The only machining is the 3/4 inch pipes with the o ring in that fit over the ends of the membrane . The rest can be easily made with absolutely no machining.
There is absolutely no danger in water pressure. My father ,who was a steam engineer all his life ,said you can be standing right next to a 3,000 psi water pipe when it bursts, in complete safety. As water doesn't compress, it doesn't expand when pressure is released either. If it were gas , it would blow you to pieces, Liquid pressure simply drops to zero as soon as the container gets the first tiny crack in it. That is why they have so many regulations for gas presure, but none for water pressure.
Pressure warnings on membrane housings are total bullshit ,to discourage you from building your own and to sucker you into buying theirs.
Brent
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Old 03-07-2007, 22:53   #15
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That leaves us with another question , does anyone have an idea on how to get (buy) a SWRO membrane so I can get started making my own watermaker ?
Preferably an online shops because I'm a resident in Europe.

Thanks and greetz.

PS Louis:
what book are you talking about ?
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