Watermaker Pickling with Propylene Glycol

[Sagittaire]

I have a Spectra Catalina 300 watermaker with an MPC-3000 controller, installed in 2005.

The watermaker’s salinity has been going up the past couple of years, along with corresponding decrease in feed water pressure. Original salinity was 150 PPM, then gradually went up to 400 PPM range, and this year it finally got to the point of salinity greater than 750 PPM which is the maximum acceptable value in the control system (all water rejected overboard, none to the tank). Feed water pressure was originally 95-100 PSI, but now is down to 82 PSI.

The problem was that I have been using propylene glycol to pickle the system during Mexico summer lay-up time periods, per Spectra’s instructions. I used PG instead of Spectra’s SC-1 storage solution because lay-up time was up to 8 months; Spectra says SC-1 is only good for 6 months, but that PG is good for a year.

Well, the Spectra Roving Rep here in Barra de Navidad, Mexico, informed me that PG can contain alcohol, which is death to the membrane. I looked at one of my bottles of PG, Camco Arctic Ban RV Antifreeze (-50 degrees F), and sure enough it says “Contains Ethyl Alcohol 64-17-5.” Ouch.

Spectra factory said that this killed my membrane by causing larger openings in it, which both reduces the pressure and increases the salinity.

I’m getting by this season by resetting the maximum acceptable salinity to 800 PPM, since the system gets it down to the 750-800 PPM range and thus delivers water to the tank. I’ve been told that the US Navy considers 800 PPM salinity to be acceptable, and the World Health Organization has a threshold of 1000 PPM. I’ll bring a new membrane down next season.

Be very careful out there if you are using PG for pickling. Make sure it does not contain alcohol.

I’m looking for a source of propylene glycol that does not contain alcohol, and is preferably rated for minus-100 degrees F as recommended by Spectra. Any words of wisdom as to source for this would be appreciated.

[bajatrawler]

I have been using Blue Ocean antifreeze (West Marine) to pickle the membrane in my Spectra Ventura 150 for many years, while the boat is laid up in Mexico. Works well and contains no alcohol.

[colemj]

I'm sure Tellie will be to this thread in good time with good advice, but maybe you should also consider the possibility that your membrane has been in use for almost nine years and it just simply reached its end of life, and had nothing at all to do with pickling with PG solution. I mean, you have been using PG for over 8 years without problem, correct?

Mark

[Sagittaire]

colemj, thanks for the post. I have only been pickling with propylene glycol for the past three years. Before then, I was using the Spectra SC-1 pickling compound. But apparently, three years was enough to kill the membrane.

[Tellie]

Colemj is right, these are the things I like to sink my teeth into. (PS, I did PM you as well) You tell the Roving rep and the factory reps at Spectra to call me because as colemj again states correctly that if this is an original membrane there is nothing abnormal going on at all with the membrane. Nine years is a very good life span on any membrane. Usually I quote five to eight years as a good life span of a well taken care of membrane. I've seen them go 12 years, but that is certainly the exception to the rule. So chances are very good that you have been doing everything right in maintaining your system up to this point. Your membrane has just simply seen better days. PG IS the better alternative for storing your watermaker. If you don't use Spectras SC-1 you can only use PG. The advantage of the PG is that not only does it store the membrane but it also protects the feed pump head and the Clark pump on your system far better than the SC-1 can and these parts are more expensive than the membrane. Now the one thing that does concern me slightly is the pressures. Normally your system should be running pressures in the 90-110psi range. The fact that you are now in the 82psi range could mean several things. That the membrane is in fact old and not offering quite as much resistance as a new one would. The fact that your system is nine years old could mean that the Clark pump is showing some signs of age and is not producing quite enough pressure. The feed pump could also be losing some pressure creating ability. Also water temperature and salinity can easily make this difference (where are you when recording these pressures?) You should do a quick flow test on the product water to make sure that you are still producing 12.5gph. Don't always trust the control panel to be super accurate when trouble shooting this area. Your resetting the PPM threshold to 800 is fine temporarily until a solution is found. Though you should have a hand held TDS meter to verify your product water. I still recommend that you use PG-100 and until the new wisdom that PG-50 is fine as well I'll hold back a bit recommending it. I hope that is enough information for you at this point.

[Sagittaire]

Tellie, muchas gracias. Much appreciated.

Sagittaire was in Mexico's Sea of Cortez at the time I started using alcohol-containing prop glycol in 2011. Three years of pickling with PG up in the Sea at San Carlos, Sonora, Mexico, where Sagittaire was stored on the hard. The summer temperature routinely reaches 95-100 deg F.

I did a flow test with a calibrated bucket and the flow was exactly the same as when the system was new: 2.3 GPM. I am getting 13 GPH when making water at 82 PSI feed water pressure and 760 PPM. Although the watermaker is 8+ years old, it only has 455 run time hours. How many run-time hours should a membrane last?

Feed pump pressure was 95 - 98 PSI during the first few years of operation, but has deteriorated since I started pickling with alcohol-containing "minus 50" PG, and now it is down to approx 82 PSI. I had 150 PPM to 200 PPM during the first year of operation with 95 PSI feed water pressure.

I'm glad to hear that the PG has been better for the mag-drive vane pump and the Clark pump. Baja Trawler referred me to West Marine's Pure Ocean PG rated at "minus 100" and hopefully does not contain alcohol. I will get this or an equivalent (hopefully less expensive) PG for future pickling.

Thank you for the PM regarding the Filmtec SW2540 membrane.

[jongleur]

Do people use sodium metabisulphite?

[Tellie]

Originally Posted by jongleur

Do people use sodium metabisulphite?

Sodium Metabisulfite is used in many watermakers. Just never in a Spectra watermaker.

[motaman9]

Speaking of Sodium Metabisulfite.....does anyone know how long a pickling is good for using that compound? I've seen some references online that some pickling processes are only good for six months before requiring a reapplication of the solution. We have only owned this boat for seven months and the prior owner said he has gone as long as a year before putting the system back in service with no issues......thanks

[ksanders]

I have a different brand of watermaker (Katadyne)

It came with a little jar of pickling powder. Just add a tablespoon to a gallon of water and run that through the watermaker.

Perhaps something like that might work in the future and be easy to stow many years worth of product.

[Tellie]

Originally Posted by motaman9

Speaking of Sodium Metabisulfite.....does anyone know how long a pickling is good for using that compound? I've seen some references online that some pickling processes are only good for six months before requiring a reapplication of the solution. We have only owned this boat for seven months and the prior owner said he has gone as long as a year before putting the system back in service with no issues......thanks

As sated above, I prefer PG over SB for a few reasons. First it is going to store your system for a longer period of time, usually a year or so. Second SB is usually recommended to be changed out every six months. PG not only stores the membranes but protects the internal parts of the rest of your watermaker far better than SB. This protection can save you a lot more future money than the cost of a simple membrane.

[motaman9]

Originally Posted by Tellie

As sated above, I prefer PG over SB for a few reasons. First it is going to store your system for a longer period of time, usually a year or so. Second SB is usually recommended to be changed out every six months. PG not only stores the membranes but protects the internal parts of the rest of your watermaker far better than SB. This protection can save you a lot more future money than the cost of a simple membrane.

Thanks.....wasn't sure if the PG was a safe alternative for all brands of membranes since the previous owner exclusively used SB.

[Dave852]

You can dilute this up to 50% with pure water from your Watermaker. Always use food grade.

[Dave852]

Tellie, I would be interested in hearing what dilution rate you would be comfortable with as the stuff is pricy compared to SM.

[thinwater]

Practical Sailor has a series of glycol articles coming out this Fall--I wrote them. A part of my day job is engine coolant manufacture and glycol manufacture, so for the engine coolant part I was on comfortable ground. The articles cover all of the traditional stuff, like burst point and corrosion (the alcohol formulas generally stunk, as did vodka). But also a few topics relevant here that I didn't think about. Perhaps I need to investigate further.

a. Yes, some brands contain ethanol, and it isn't always marked on the label, since some are ethanol/PG blends. Camco Articban and Sudbury Winter Stor were 2 that contained ethanol, but honestly, I was trying to avoid ethanol.

b. Corrosion protection varies. If you have brass or aluminum in the system there are some big differences. Again, avoid ethanol.

c. Bio growth varied. NEVER go below 25% glycol (-50 BP); bugs can eat anything less than that, once they get acclimated. You might get away with it, you might not. pH also matters; products with pH 8 did better than products with pH 7 or less. We did trials with plain PG, adjusting the pH with caustic; same correlation.

Any other important factors?