misc WaterMaker questions

[markxengineerin]

I have finally gotten around to using my Spectra 380C watermaker more regularly, and a few questions have come up. I am operating in full manual mode, no electronics.

1) What's the best way to perform a fresh water flush? The user manual suggests two methods. One seems to involve pumping fresh product water through the membrane, under pressure, until the feed pressure drops then add 1 more minute. The other method involves pumping 5 gallons of fresh product water through the membrane housing, but under low (no?) pressure, as the pressure relief valve on the clark pump is open 1/2 turn. Both methods are tough right now because my "cleaning bucket" only holds about 4 gallons in a seaway- maybe need to add a 2nd.

2) How long do you comfortably go between uses, no pickling and no Z ion system? I have been ok with a week in cold climates, but now in Florida. Anecdotally, I hear that a week is also fine here, but Spectra recommends 3 days. Would symptoms of a clogged membrane be subtle, or obvious?

3) Do you store your pre-filters “dry” between uses? How often to clean them, and how often to replace? Here is an example of the 25 micron after making 90 gallons about 5 miles off the coast of Georgia, with half of it sprayed with a garden hose to clean. The 5 micron that comes next still looks clean.

I don't have any reference point for if this level of fouling is normal, if I should be spraying it off after every use, if the fouling here may affect the safe storage time for the RO membrane, etc.

Thanks for any tips, and please note your climate for reference.

[noelex 77]

1. The best method is to measure the PPM of the brine water discharge. The correct flush length is when this drops to below 1000 ppm.
2. Fresh water flush should be done every 5 days. Colder weather helps reduce growth, but personally I would not try to extend the recommended cycle.
3. Yes, storing dry is best.

PS that does not look like a genuine Spectra pre filter. String wound filters cannot normally be cleaned and reused.

Climate is everything mother nature throws at us . Currently it’s warm.

[markxengineerin]

Thanks- not a Spectra pre-filter, so I'll try to find some pleated ones like they refer to in the manual. The filters I have seem like they might take 5+ days to really dry, especially if it's cold/humid, but maybe exposing them to air is better than sitting in water? Good tip on the brine discharge measuring- I have an extra sensor I'll rig up for that.

[wrwakefield]

We have a similar age manual Specra watermaker (Santa Cruz; single membrane; dual infeed pumps; 11-14 GPH- depending upon raw water temp and salinity.)

Per your questions:

We use both fresh backflushing methods: the first after a desalination run to preserve fresh water. The 2nd when we haven't used the WM for 5 days.

Dry storage of prefilters is best over long periods of no use- even if backflushing every 5 days.

And you can pickle the WM system with 100% RV antifreeze (propolene glycol) for up to a year.

In case this is useful.

Cheers, Bill

[noelex 77]

Originally Posted by markxengineerin

Good tip on the brine discharge measuring- I have an extra sensor I'll rig up for that.

You can just use the handheld sensor.

Rinse the water maker for longer than needed and collect several brine samples noting the time. The time when it comfortably below 1000ppm (some recommend 800ppm) is correct. This can be verified on the next rinse by collecting a brine sample at the end.

If nothing else changes in the set up, this same rinse time should be OK without having to measure it every time.

[Tellie]

I agree with Nolex on the freshwater flush set up. If you don't get the brine discharge down below 1000PPMs you are not flushing correctly. Just adding time to the freshwater flush is not always the answer to a good flush. Setting up the freshwater flush can be a bit if a chore matching feed pump motor speeds to the input pressures and flows of the boats freshwater pump so that the freshwater flush does not draw up and mix a bit of salt water through the intake thru hull. If your system is set up to flush with the thru hull in the open position, then this set up is critical to get right. Even a minute amount of salt water intrusion during the freshwater flush will ruin the flush. You could flush for hours like this and never achieve a proper flush. Second, loose the string wound filter and find the proper pleated ones to use. I have them if you can't source them. String wound filters restrict flows of water and they have a tendency to give off very fine fibers from the string that end up in check valves, springs, membranes, etc. You can easily pinch off some of these fibers with ease to see this.

[markxengineerin]

Thanks Tellie and everyone, I have taken all the advice and will report back after some trials. My system totally blocks the salt water feed during flushing, but it still seems to take more than 4 gallons to get down to 1000 PPM, at least on my first trial.