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Old 13-01-2011, 18:08   #1
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Semi-Technical Watermaker Questions

I am continuing to move forward with my watermaker design and parts procurement. But there are a couple of things that I have not worked out yet so any help from those with any experience is valued. My system should provide between 36-40 product gallons/hour,

I thought about installing a pressure transducer at the input to the high pressure pump to sense the input filters condition. But there are a lot of buts. For example, I have no clue about the normal pressure drop one can expect with a set of filters and of course, I would guess that depends a lot on the physical size of the filters. The fluid flow rate will be 3.2 gal/minute.

Next there is the pressure developed at the priming pump's output ..........if any at all. And to complicate matters, I have not selected this pump yet. I am at a loss about how to design a sensor circuit for the input to the high pressure pump because I don't know what pressure to expect with both good and bad input filters.

For all I know before I get a machine built, the pressure at the input to the high pressure pump could be negative (a vacuum condition) in which case, a pressure transducer won't cut it. But would the input pressure be negative with both good and bad input filters?? My goal is to use transducers followed by digital meters for all metering and eliminate plumbing to and from flow gages and pressure gages of various types.

To date, I have quite a few parts that include my AC (2HP) AC motor, high pressure pump, seawater pressure vessels, flow transducers, high pressure transducer, back pressure regulator, many digital panel meters, high pressure solenoid valve and a high pressure regulator to soften the startup surge on both the electrical circuit and the seawater membranes and my parts list goes on. I am getting close to purchasing SS pipe and fittings.

Foggy
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Old 13-01-2011, 19:42   #2
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Not sure you posted answer to this question on another thread, but whose design for the watermaker are you using, Guy Stevens (http://captainwiki.com/images/2/2d/W...e_Your_Own.pdf . I'm about to embark on same project, I'll stay tuned to this thread.

I wonder what has been the experience of our CF members on their own home-built watermakers. At this point, there has to be some who have 5+ years of experience with their units. Are they still happy they saved 2-3k of up front costs? Do their units still operate well? Just curious.
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Old 14-01-2011, 06:50   #3
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Originally Posted by foggysail
I am continuing to move forward with my watermaker design and parts procurement. But there are a couple of things that I have not worked out yet so any help from those with any experience is valued. My system should provide between 36-40 product gallons/hour,

I thought about installing a pressure transducer at the input to the high pressure pump to sense the input filters condition. But there are a lot of buts. For example, I have no clue about the normal pressure drop one can expect with a set of filters and of course, I would guess that depends a lot on the physical size of the filters. The fluid flow rate will be 3.2 gal/minute.

Next there is the pressure developed at the priming pump's output ..........if any at all. And to complicate matters, I have not selected this pump yet. I am at a loss about how to design a sensor circuit for the input to the high pressure pump because I don't know what pressure to expect with both good and bad input filters.

For all I know before I get a machine built, the pressure at the input to the high pressure pump could be negative (a vacuum condition) in which case, a pressure transducer won't cut it. But would the input pressure be negative with both good and bad input filters?? My goal is to use transducers followed by digital meters for all metering and eliminate plumbing to and from flow gages and pressure gages of various types.

To date, I have quite a few parts that include my AC (2HP) AC motor, high pressure pump, seawater pressure vessels, flow transducers, high pressure transducer, back pressure regulator, many digital panel meters, high pressure solenoid valve and a high pressure regulator to soften the startup surge on both the electrical circuit and the seawater membranes and my parts list goes on. I am getting close to purchasing SS pipe and fittings.

Foggy
I would be more focused on flow rate then pressure. You'll find with differing salinity and water temps that the operating pressures can vary quite a bit.

Are you using an electrically adjustable pressure regulator ( back pressure regulator). Or just a manual one.

Dave
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Old 14-01-2011, 08:35   #4
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Dave, the back pressure regulator is a Cat 7370 manual valve. I did not even seek out an electrical valve with a possible feedback loop (servo) because my pump is driven at a constant RPM via the electric motor.

But you bring up a good point about watching the flow rate!!! I have a pair of flow sensors (transducers) but again, that brings up another but. For example, my plan was to install one just ahead of the high pressure pump which should work out just fine. However there will be about a 3 psi pressure drop across the flow sensor at my flow rate of 3.2 g/hr. How much that will impede the system is moot to me at this time.

I have a second pressure regulator that I plan to mount in parallel to the Cat. This regulator will be set to a lower pressure, maybe about 350-400 psi that will be activated with a high pressure solenoid during system start up.

Chris--- I lost count at how many DIY watermakers I have looked at. The one that gave me the greatest insight is Glen Ashmore's. Mine is not a direct copy by any means but one that is providing a guide.

For example, Glen used typical flow gages to monitor flow rates. He is not clear on many aspects of his design as I plodded ahead. But I am using many of his ideas such as a frequency to to voltage converter to count pulses from flow transducers. That voltage will drive a panel meter as will a current source high pressure transducer that will meter the pressure at the membrane. Glen used a frequency to voltage converter to control against a variable engine RPM problem.

Just finding components can be mind boggling!!! I spent almost a month looking for a high pressure solenoid valve which I ordered this morning. Pressure vessels.......another search effort but no where as involved as the stinking pressure solenoid. And so it goes--

Foggy
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Old 14-01-2011, 11:24   #5
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Originally Posted by foggysail View Post
Dave, the back pressure regulator is a Cat 7370 manual valve. I did not even seek out an electrical valve with a possible feedback loop (servo) because my pump is driven at a constant RPM via the electric motor.
a simple needle valve would do then.


Quote:
But you bring up a good point about watching the flow rate!!! I have a pair of flow sensors (transducers) but again, that brings up another but. For example, my plan was to install one just ahead of the high pressure pump which should work out just fine. However there will be about a 3 psi pressure drop across the flow sensor at my flow rate of 3.2 g/hr. How much that will impede the system is moot to me at this time.
given the pressures involved in the high side, 3psi is neither here nor there.

Quote:
I have a second pressure regulator that I plan to mount in parallel to the Cat. This regulator will be set to a lower pressure, maybe about 350-400 psi that will be activated with a high pressure solenoid during system start up.
Why that for , is that to allow the priming system to start first , it will never generate 300 psi. whats it for.

Quote:
Chris--- I lost count at how many DIY watermakers I have looked at. The one that gave me the greatest insight is Glen Ashmore's. Mine is not a direct copy by any means but one that is providing a guide.
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Old 14-01-2011, 16:01   #6
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Originally Posted by goboatingnow View Post
a simple needle valve would do then.


given the pressures involved in the high side, 3psi is neither here nor there.

Why that for , is that to allow the priming system to start first , it will never generate 300 psi. whats it for.

Dave

Things got lost in translation plus my typo. The flow rate into the system is 3.2g/minute........mistakenly typed g/hr.

And yes, I agree that a simple needle valve could have satisfied my application but I purchased the CAT. A needle valve is not a regulator, regulation just happens because flow is diverted and flow will always be diverted regardless of the pressure.

Your last comment must be related to my second pressure regulator paralleled with the CAT. That second regulator will be energized during two phases of operation. The first phase is during start up. I DO NOT WANT THE PUMP TO COME UP TO 800psi IMMEDIATELY. I want the pressure to be stepped, first up to 350-400 and finally to a step to 800. This is the best I can do to prevent pressure transients being applied to the membranes in one step. Dow recommends the pressure be applied gradually. I cannot do that but I can step the pressure.

There is another reason, more than likely a more important reason and that is related to the motor's surge current. When the motor is energized, a surge current will occur because of the motor's magnetizing inductance (locked rotor conditions until the motor acquires speed). That surge will happen whether there is a load or no load. Next there is a surge current (occurring at the same time as the magnetizing current) that is directly related to the load... the pump. It has nothing to do with the priming pump what so ever.

I'm stuck with the magnetizing current but I can control when it occurs so that will happen with th pump pumping at a lower pressure (load). Then after a few seconds, the lower pressure regulator will be locked out by a pressure solenoid.

Stepping the load will help prevent circuit breakers from tripping. I want to run this system on 120V not 240.

The final reason for being able to switch the membrane pressure down to 350-400 is for flushing the membranes.

Foggy
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Old 14-01-2011, 16:22   #7
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Quote:
Originally Posted by foggysail View Post
Things got lost in translation plus my typo. The flow rate into the system is 3.2g/minute........mistakenly typed g/hr.

And yes, I agree that a simple needle valve could have satisfied my application but I purchased the CAT. A needle valve is not a regulator, regulation just happens because flow is diverted and flow will always be diverted regardless of the pressure.

Your last comment must be related to my second pressure regulator paralleled with the CAT. That second regulator will be energized during two phases of operation. The first phase is during start up. I DO NOT WANT THE PUMP TO COME UP TO 800psi IMMEDIATELY. I want the pressure to be stepped, first up to 350-400 and finally to a step to 800. This is the best I can do to prevent pressure transients being applied to the membranes in one step. Dow recommends the pressure be applied gradually. I cannot do that but I can step the pressure.

There is another reason, more than likely a more important reason and that is related to the motor's surge current. When the motor is energized, a surge current will occur because of the motor's magnetizing inductance (locked rotor conditions until the motor acquires speed). That surge will happen whether there is a load or no load. Next there is a surge current (occurring at the same time as the magnetizing current) that is directly related to the load... the pump. It has nothing to do with the priming pump what so ever.

I'm stuck with the magnetizing current but I can control when it occurs so that will happen with th pump pumping at a lower pressure (load). Then after a few seconds, the lower pressure regulator will be locked out by a pressure solenoid.

Stepping the load will help prevent circuit breakers from tripping. I want to run this system on 120V not 240.

The final reason for being able to switch the membrane pressure down to 350-400 is for flushing the membranes.

Foggy

Hey Foggy, I thought a DIY watermaker was easy.
Sounds like you have really done your homework, good on you. How many hours do you think you have in the project so far? How about some pics for us to see your progress? Just a hint. On the pre-filters, setting up sensors to read a vacuum to indicate dirty filters may be a bit of over kill. Usually even people with all the electronics on their watermakers end up just getting a feel when it is time to change them out. Not trying to discourage your plans just a view from over the years.
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Old 14-01-2011, 16:57   #8
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G'day, Foggy. Before I offer to much input based on my experience over the years, do you want a system that you just hit the start button and it controls itself or do you want to manually monitor the system (which means the relative flow and pressure guages will have to be easily accesible) and make adjustments (it appears that you may want the later)?

I have a 20 gal/hr system that runs automatically, plus I can make adjustments if necessary. Your system is going to run in the 900 to 1000 psig range when it making good water. It takes about 30 seconds for my system to come up to pressure. Currently going on 9 years on my current set of membranes. Cheers,
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Old 14-01-2011, 17:52   #9
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G'day, Foggy. Before I offer to much input based on my experience over the years, do you want a system that you just hit the start button and it controls itself or do you want to manually monitor the system (which means the relative flow and pressure guages will have to be easily accesible) and make adjustments (it appears that you may want the later)?

I have a 20 gal/hr system that runs automatically, plus I can make adjustments if necessary. Your system is going to run in the 900 to 1000 psig range when it making good water. It takes about 30 seconds for my system to come up to pressure. Currently going on 9 years on my current set of membranes. Cheers,

Matauwhi--

GEEZ, 9 years on membranes!!! You must be doing something right. Pressure-- what ever is needed it will be. But 900+ seems a little on the high side but again--- I am only playing with paper, pen, ROSA and a lot og guess work. It the machine does require 900+, I will have a problem because I am pushing my limits for a 2HP motor. A three HP motor has an entire set of its own problems. OH-- I am striving to make my machine automatic. Thank you for taking the time to share your experience.

Foggy
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Old 14-01-2011, 18:12   #10
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Hey Foggy, I thought a DIY watermaker was easy.
Sounds like you have really done your homework, good on you. How many hours do you think you have in the project so far? How about some pics for us to see your progress? Just a hint. On the pre-filters, setting up sensors to read a vacuum to indicate dirty filters may be a bit of over kill. Usually even people with all the electronics on their watermakers end up just getting a feel when it is time to change them out. Not trying to discourage your plans just a view from over the years.

Tellie--- I am sitting at my desk typing while doing belly roles reading your post!!!!

Have to remember---- I just needed a winter project. Sometimes I get cranked and spin myself, sometimes hopelessly down a rat hole. But I just enjoy technical projects. HOURS???YA KIDDING! And....did I say these things are simple??? I must have been hallucinating.

And thank you for comments on my home work. Pictures--- about all I have are piece parts so far BUT I certainly will share as much as I can with those who seek information. GEEZ.... I spent a month just finding a SS high pressure solenoid valve with low pressure drop (1/4 NPT). One company, STC wanted almost $400 for theirs. I ended up purchasing a Danfoss for almost half that cost.

Tellie---- this is not for a novice, but you know that.

Some of my past foolishness includes the time (years ago) I built my own color TV set, built my own house, designed, built some windmills with plans to manufacture them, did all my own canvas work for the boat. I know I can think of more but that's enough. And yes-- I will take your advice and ignore filter vacuum/pressure readings.

Foggy
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Old 17-01-2011, 18:05   #11
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G'day again, mate. O.K. if you want an automatic system, then you are going to have research a salinity or TDS (total disolved solids) meter to control your solenoid valve. You can keep an eye on Ebay or Craigslist for some older automatic watermaker systems that had the salinty monitors. Also, depending on your installation location, you may need a booster pump to maintain your 3.5 gpm flowrate to your high pressure pump. Not sure what type of pre-filters you will be using, but on my experience, you will want to use the 5 micron 9 inch filters and relative pressure housing that you can find at the typical discount hardware store.

You should also give some thought on how you are going to run your watermaker in conjunction with your other electrical requirements on the boat. For example, will you be using a genset to run it, and if so, how long do you think you will need to run your genset to meet your total electrical needs? This helps determine the appropriate size of your watermaker, along with your daily water requirements. Cheers.
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Old 17-01-2011, 19:11   #12
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G'day again, mate. O.K. if you want an automatic system, then you are going to have research a salinity or TDS (total disolved solids) meter to control your solenoid valve. You can keep an eye on Ebay or Craigslist for some older automatic watermaker systems that had the salinty monitors. Also, depending on your installation location, you may need a booster pump to maintain your 3.5 gpm flowrate to your high pressure pump. Not sure what type of pre-filters you will be using, but on my experience, you will want to use the 5 micron 9 inch filters and relative pressure housing that you can find at the typical discount hardware store.

You should also give some thought on how you are going to run your watermaker in conjunction with your other electrical requirements on the boat. For example, will you be using a genset to run it, and if so, how long do you think you will need to run your genset to meet your total electrical needs? This helps determine the appropriate size of your watermaker, along with your daily water requirements. Cheers.

First--Thank you for your reply.

Yes, I have stated I plan to go automatic with the design but I am backing away slighty. It been a bitch just finding some parts and I already purchased a CAT 7370 back regulator so the one thing that WILL require attention is the pressure. Now I am still a learning novice in watermankers. Maybe its not pressure that I need to watch but rather product. In any case, the pressure is going to be set manually which should not require frequent changes with an ac motor driven pump.

What will be automatic is stepping the pressure as mention in one of my recent posts, operating the maker for a set time until I can put together a tank full sensor circuit to curtail production and finally an automatic flush cycle after every use. That is very important because I could not afford the big bucks for a bronze pump nor the much bigger bucket of bucks for a SS one. How long with the pump last? I hope years but I base my hope on other's experience using brass but flushing it after usage.

Two other things that I intend to implement but maybe not activate at the beginning until I get some experience with it is a shut down based on low product and also high dissolved solids.

Booster pump! Right on, I see that necessary. I have a pump but its overkill for that purpose at 1/3HP. I plan to look at the pump used for my AC. It might not have the flow rate but I will check it out. That has an advantage of a magnetic coupling between the motor and the pump proper. So if any debris stops the pump, it won't fry the motor driving it.

Electrical load-- HEY!!! You have some well thought out suggestions! But back to the electrical. If I run the system at the dock....and I do plan to, then all the AC power will need to be dedicated to the water maker. I had to make a trade off at the start before purchasing a pump along with the needed motor.

At first I was going to use only the generator to power the system along with a 3HP motor. That would have increased my product to over 40 g/hr without problems but that in itself became a problem. I could find zero 6 pole motors that operate on single phase nor could I find ANY 3HP motors during my search that operated at 1750RPM!! A 6 pole single phase motor operating at 240 would be ideal. There would be less vibration, the pump would wear longer because of the slower RPM (1150RPM) I could only find 3HP single phase motors that operate at 3600RPM. Won't work!!!

So I back down to a 2HP and opened my options to operate at 120VAC using either gen or dock power. But I am at the limit of that motor with a 3.2g/minute pump and that flow rate yields a more realistic product of about 36 g/hr rather than 40+.

Now I need to be careful with inrush currents as I mentioned earlier in a prior post. But planning for about 85% efficiency with the motor, I expect my steady state line current to be about 15 amperes which is fine for a 20 ampere circuit.

When operating on the genny, there is no power problem because it is rated for 7.5KW or over 3KW for 2 each 120VAC distribution circuits which teh boat's electrical center has.

Again-- thank you for your reply

Foggy
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Old 17-01-2011, 19:55   #13
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G'day, Foggy, Well, in my opinion, if you are going to have to flush your pump everytime, then I would stick with a manual system. It will be much simpler. I have a bronze CAT pump, so I very rarely flush the system. I do run it most everyday. I also have a 8 kw 120 volt AC genset. We use about 10 gallons a day, so in a half hour have running the system have met our usage.

It has been my experience that I rarely need to make adjustment to my pressure regulator. And again, in my opinion, based on my experience and demonstrated membrane life, I wouldn't worry about stepping up the pressure when you start the system. Just let your back pressure regulator do the job.

If you are going to use a booster pump, along with your high pressure pump, you are going to need more than 20 amps. More like 30 to 40 amps. You will get by on 20 amps for your high pressure pump, but not with the 1/3hp booster pump. Cheers.
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Old 17-01-2011, 20:22   #14
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My bilge outlet is below the water line when boat lists in the marina due to wind from off side.My question is if I loop the outlet pipe up above the water level by a foot or more it should stop the ingress of water through the bilge pump I think??? I'm also going to install a non-return valve in the manual pump line am I doing the righ thing???
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Old 17-01-2011, 21:41   #15
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Originally Posted by matauwhi View Post
G'day, Foggy. Before I offer to much input based on my experience over the years, do you want a system that you just hit the start button and it controls itself or do you want to manually monitor the system (which means the relative flow and pressure guages will have to be easily accesible) and make adjustments (it appears that you may want the later)?

I have a 20 gal/hr system that runs automatically, plus I can make adjustments if necessary. Your system is going to run in the 900 to 1000 psig range when it making good water. It takes about 30 seconds for my system to come up to pressure. Currently going on 9 years on my current set of membranes. Cheers,
That's impressive.
Is your watermaker bought or DIY?
If bought, what make and model, and to what do you attribute the long service you're getting out of your membranes?
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