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Old 29-07-2012, 05:06   #1
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Watermaker output vs water temperature?

Is there a formula or chart I could use to estimate how much reduction in watermaker output I should expect as water temp varies? My Spectra Catalina is rated for 1 GPM and I think that's at 77F. I'm trying to estimate how much that will drop with water temps of 60F, 50F, 40F etc.

I think I'm getting about 8 GPM, but I've been in 50F or so water at the time. I know salinity also affects output, but I'm just trying to get a sense of the temperature impact.

Thanks
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Old 29-07-2012, 05:23   #2
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Re: Watermaker output vs water temperature?

Waa you don't ask me?
You might be a bit confused with the difference between production and flow. The gallons per minute flow is a nominal flow measured from the brine discharge and product water together. On your Catalina that flow should be 2.3 gallons per minute.
Your Catalina is rated at 12.5 gallons of product water made per hour. Though temperature and salinity will make a difference in the ppms it will not, unlike other watermakers, make a difference in production. If you are only getting a measured 8 gallons per hour product water and 1 gallon per minute flow from your Catalina there is something wrong and it has nothing to do with temperature and salinity.
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Old 29-07-2012, 06:11   #3
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I'm glad you replied. The reason for asking here rather than directly was so others could benefit from the answer....

Interesting response, though. I'm talking about product water rate, which i think is what the MPC display reports. Is the constant production because the MPC varies pressures etc to compensate for varying salinity, water temp, etc? I think it was Spectra's literature where I first learned that product output decreases with colder water.

Anyway, the longer story is that when I commissioned this maker in the spring, I encountered a broken fitting and broken flow rate meter (the whirly thing). It's hard to imagine how they got broken given the way the unit was packed and shipped, but regardless Spectra was great getting me replacement parts. When i replaced the flow meter, I did no recalibration.

When running the maker, the MPC reports 14 GPM, more or less, which I gladly accepted. But after 3 and 6 hrs runs, my tank level gauges show replenishment more in line with 8GPM. With one exception, I've been in freekin cold water, say in the 50s when making water, even though I've see 36F on this trip.

I've attributed the production discrepancy to cold water and the need to calibrate the new meter, and just today started to research how much production should vary with temp to validate the theory. I know I need to crack the output line and measure product output, but I probably won't get to that until I get home. So in the mean time, I'm trying to learn about the effects of water temp on product output.
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Old 29-07-2012, 11:01   #4
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Re: Watermaker output vs water temperature?

Quote:
Originally Posted by twistedtree View Post
I'm glad you replied. The reason for asking here rather than directly was so others could benefit from the answer....

Interesting response, though. I'm talking about product water rate, which i think is what the MPC display reports. Is the constant production because the MPC varies pressures etc to compensate for varying salinity, water temp, etc? I think it was Spectra's literature where I first learned that product output decreases with colder water.

Anyway, the longer story is that when I commissioned this maker in the spring, I encountered a broken fitting and broken flow rate meter (the whirly thing). It's hard to imagine how they got broken given the way the unit was packed and shipped, but regardless Spectra was great getting me replacement parts. When i replaced the flow meter, I did no recalibration.

When running the maker, the MPC reports 14 GPM, more or less, which I gladly accepted. But after 3 and 6 hrs runs, my tank level gauges show replenishment more in line with 8GPM. With one exception, I've been in freekin cold water, say in the 50s when making water, even though I've see 36F on this trip.

I've attributed the production discrepancy to cold water and the need to calibrate the new meter, and just today started to research how much production should vary with temp to validate the theory. I know I need to crack the output line and measure product output, but I probably won't get to that until I get home. So in the mean time, I'm trying to learn about the effects of water temp on product output.

It gets a bit complicated here to explain the product rate on a Spectra because of how it works differently than just standard high pressure plunger pumps. Water temperature certainly affects product output on most watermakers and the pressure on those systems need to be adjusted, especially in waters nearing 36F so as not to cause damage to the watermaker. But your Spectra operates on a different principal than just brute force from a high pressure pump. It self adjusts compensating for the temperature differences internal to the Clark pump. I have charts for Sea Recovery, Village Marine etc. that show what you are looking for and make perfect sense for high pressure plunger pump watermakers. But they simply do not apply to your Spectra. The MPC controls report pressures and salinity the MPC itself does not control it. But it's good to know that this is a brand new unit. If you are getting 14gph according to the MPC panel I would say that your unit is probably working just fine. The roto flow meter that you replaced may need to be claibrated to the MPC5000 to be as accurate as possible. My intial guess, since I'm not there, is that you are making close to 14gph and a product flow test will confirm it. Be careful at first in trusting your tank guages as well. The first thing you have to know is the actual production rate by doing the measured bucket and stop watch test to determine the actual amount of product made per hour then calibrate that in the flow constant from the MPC5000 control panel. This procedure is a bit complicated to explain here because the flow readings are heavily damped, but the procedure should be in your manual. I would be happy to walk you through it on the phone when you are there at the boat. Also, Spectra is a bit conserevative in it's product flow reporting. Each system is different for many different reasons, usually due to different installs. No two watermakers are exactly the same, it's the nature of the beast and inherent varying qualities of membranes out of anyones control. That aside, your unit is rated for a conservative 12.5 gph. If it, and they often do, make more than that you are tickled pink. If it was rated at 14gph and it only made 13.5 gph you'd be calling in asking what's wrong. Look for close averages between 12.5 and 14gph and all is well. Let me know if you have any questions.
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Old 30-07-2012, 07:48   #5
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Re: Watermaker output vs water temperature?

I own and use a Spectra Newport 400 II

The other thing about Spectra product flow is it is directly related to Voltage... IN other words SPECTRA water makers live VOLTAGE!

On my unit, the difference between running the water maker on the 12 volt battery bank only or running the water maker with the battery charger/engine running is huge.

Running on the house battery bank only (charged), I make about 16.0 GPH. I make about 17.5 GPH when running the battery charger or the engine alternator.

The voltage difference between the two battery states is about 1.0 to 1.5 volts.

We considered this with the installation and oversied the power cable to the unit so there is no power drop.
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Old 30-07-2012, 09:29   #6
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Re: Watermaker output vs water temperature?

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Originally Posted by jeremiason View Post
I own and use a Spectra Newport 400 II

The other thing about Spectra product flow is it is directly related to Voltage... IN other words SPECTRA water makers live VOLTAGE!

On my unit, the difference between running the water maker on the 12 volt battery bank only or running the water maker with the battery charger/engine running is huge.

Running on the house battery bank only (charged), I make about 16.0 GPH. I make about 17.5 GPH when running the battery charger or the engine alternator.

The voltage difference between the two battery states is about 1.0 to 1.5 volts.

We considered this with the installation and oversied the power cable to the unit so there is no power drop.

Very good point Jeremiason, I should have added that. You are correct. Voltage does make a difference. It should be measured at the watermakers terminals while the unit is running to get a good idea as the real voltage to the unit. I would consider 12.5 at the terminals to be the least amount of voltage for the unit to run at spec. While running the genset or engines alternators, voltage, by way of charging will certainly increase and the feed pump will simply run faster at higher voltages. On your NPMKII there is a variable motor speed drive. If your voltages are 12.5 plus at the terminals running directly off the house bank without the genset or alternator and your production is only 16gph, (accuratly measured by calibrated container and stop watch not the MPC display panel, and the pre-filters are new and the membrane is in good condition 400ppms or less) then you can slightly speed up the drive to get the 16.5 gph the NPMKII is rated for. You can take ten exactly alike watermakers and run them under the same conditions and they will all have different spec numbers. It's just the way things are in the real world. They should all be pretty close in numbers but they are all capable of being tweaked to run at spec.
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Old 30-07-2012, 10:19   #7
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Re: Watermaker output vs water temperature?

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Originally Posted by Tellie View Post
Very good point Jeremiason, I should have added that. You are correct. Voltage does make a difference. It should be measured at the watermakers terminals while the unit is running to get a good idea as the real voltage to the unit. I would consider 12.5 at the terminals to be the least amount of voltage for the unit to run at spec. While running the genset or engines alternators, voltage, by way of charging will certainly increase and the feed pump will simply run faster at higher voltages. On your NPMKII there is a variable motor speed drive. If your voltages are 12.5 plus at the terminals running directly off the house bank without the genset or alternator and your production is only 16gph, (accuratly measured by calibrated container and stop watch not the MPC display panel, and the pre-filters are new and the membrane is in good condition 400ppms or less) then you can slightly speed up the drive to get the 16.5 gph the NPMKII is rated for. You can take ten exactly alike watermakers and run them under the same conditions and they will all have different spec numbers. It's just the way things are in the real world. They should all be pretty close in numbers but they are all capable of being tweaked to run at spec.
Back at you - Extremely good point!

When our pump control curcuit board failed last year we had it replaced, but the local Spectra Tech didn't know about the magnetic speed control switch on the board (Assuming it was preset at the factory).

With the new cicuit board, the producition hovered around 13.5 GPH and the Tech blamed it on the membrane and sai dI needed a new one...

Thinking the membrane failing at the same time as the curcuit board seemed like a suspicious concidence, I began reading manuals.

It it took me a full day of reading both the manual and the Spectra Web Site to find that little magnetic switch, before I was able to bump the speed up to proper output to proper levels.

According to Spectra the speed control can be adjusted to different environments...
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Old 30-07-2012, 10:53   #8
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Re: Watermaker output vs water temperature?

Always good to question when a new problem seems to all of a sudden pop up after another one is fixed. I would have questioned the techs findings about the membrane as well. Trying to get people to fill out the card in the back of the manual is hard enough, finding someone who will spend all day reading the manual is a rarity. Good on you. As you know these things have a bit of a learning curve. There's a lot of information all at once that kind of needs to be absorbed fairly soon as to keep a watermaker working well. You sound like you have most all of it down pretty well, but if you ever need any advice don't hesitate to contact me. A quick PM will get anyone my phone number as well.
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