Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 09-03-2018, 03:50   #1
Registered User
 
Renx's Avatar

Join Date: Aug 2016
Location: On a boat
Boat: Amel Super Maramu
Posts: 12
Watermaker back flushing - is she right?

Like me, you've probably spend countless hours wondering about carbon filters and back flushing your watermaker

I've been pondering a re-build of the basic pre-filter system on my 20 year old Dessalator Watermaker - see attached image - and working out the best way to add a carbon filter for back flushing.

Then in the middle of my complex circuit diagram my wife suggested just swapping out the string pre-filter for a carbon filter when doing the back flush from the water tank.

Please tell me this is a bad idea so I don't have to admit I've wasted countless hours and copious amounts of paper

Cheers..

Woody
@mothershipadrift
Attached Thumbnails
Click image for larger version

Name:	Watermaker 01 labelled.jpg
Views:	226
Size:	429.6 KB
ID:	165811  
__________________

Renx is offline   Reply With Quote
Old 09-03-2018, 04:34   #2
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,319
Re: Watermaker back flushing - is she right?

It looks like the Admiral is right. It would work but it will become a pain after a while doing this say every other day, plus the water spillage. I'd be willing to bet you'll be adding a charcoal filter housing to the mix fairly soon. I assume the plumbing you pictured is all going away in your rebuild? If it is, as it should (especially the thin walled copper piping) I would just go ahead and plumb in the charcoal filter. Any standard clear housing should work fine, maybe an extra $40 in expense, well worth the investment.
Tellie is offline   Reply With Quote
Old 09-03-2018, 12:22   #3
Registered User

Join Date: Jan 2008
Location: SF Bay Area (Boat in La Paz)
Boat: Valiant V40
Posts: 571
Re: Watermaker back flushing - is she right?

As Tellie suggests, but be sure to plumb the charcoal filter on the fresh water side before the 3-way valve so raw sea water does not go through it.
jamhass is offline   Reply With Quote
Old 09-03-2018, 17:19   #4
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,319
Re: Watermaker back flushing - is she right?

PS: No string wound filters. Use quality pleated filters.

PSS: "is she right?"

You must be a newly wed.
Tellie is offline   Reply With Quote
Old 10-03-2018, 21:07   #5
Registered User

Join Date: Feb 2015
Location: Oakland CA, boat on the hard in Panama
Boat: Morgan 46 ketch
Posts: 768
Re: Watermaker back flushing - is she right?

We have a carbon filter in the output of our fresh water tanks, just before the water goes to the fresh water pressure pump. So ALL fresh water in the boat is carbon filtered. There is no issue with flow rate (we have the galley, two showers, fresh water on deck and a washing machine, sometimes two or more drawing water at the same time). Its just a standard size filter. If you simply carbon filter all your water as it leaves the tanks then you can obviously make any connection to that system that is convenient, for the backflush. Or maybe I just didn't understand your question.
waterman46 is offline   Reply With Quote
Old 11-03-2018, 08:53   #6
Registered User

Join Date: Nov 2014
Boat: Hylas 54
Posts: 149
Re: Watermaker back flushing - is she right?

Could be wrong, but you are not actually back flushing with fresh water. You are flushing in same direction as the seawater but just getting rid of any seawater from the membranes for short term storage. And the filter is not there to remove particulate matter but to remove any trace of chlorine in the water. Thus a regular particle filter will not work. Chlorine will ruin the membranes fast.

That is why itís ok to wash the membranes with RO water you have made. But not good to rinse with freshwater you may have put in your tanks from a chlorinated domestic supply.

Others are probably more able to assist, but I think a ordinary household filter may be a quick path to shorten your membrane life span.
Hobiehobie is offline   Reply With Quote
Old 11-03-2018, 09:31   #7
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,319
Re: Watermaker back flushing - is she right?

Quote:
Originally Posted by Hobiehobie View Post
Could be wrong, but you are not actually back flushing with fresh water. You are flushing in same direction as the seawater but just getting rid of any seawater from the membranes for short term storage. And the filter is not there to remove particulate matter but to remove any trace of chlorine in the water. Thus a regular particle filter will not work. Chlorine will ruin the membranes fast.

That is why itís ok to wash the membranes with RO water you have made. But not good to rinse with freshwater you may have put in your tanks from a chlorinated domestic supply.

Others are probably more able to assist, but I think a ordinary household filter may be a quick path to shorten your membrane life span.

Tellie is offline   Reply With Quote
Old 11-03-2018, 13:00   #8
Registered User
 
mvmojo's Avatar

Join Date: Mar 2018
Location: www.mvmojo.com
Boat: Robt Beebe Passagemaker 49-10 in steel
Posts: 191
Re: Watermaker back flushing - is she right?

Waterman46 has the right idea. Carbon filter the output of your fresh water pump and plumb it to a 3 way valve on the input of your RO seawater pre-filter. Flip the valve and you're flushing both your pre-filter and your membrane with carbon filtered water from your tanks. We flush every time we run the watermaker for 2-3 minutes. I'd recommend you also install a tee so you can easily winterize the watermaker or do an acid flush. BTW, the pink antifreeze makes a good preservative for the membrane and keeps it from freezing. Sodium metabisulfite, the conventional preservative, does not appreciably lower the freezing point of water and therefore does not act as an antifreeze.
mvmojo is offline   Reply With Quote
Old 14-03-2018, 12:28   #9
Registered User

Join Date: Feb 2015
Location: Oakland CA, boat on the hard in Panama
Boat: Morgan 46 ketch
Posts: 768
Re: Watermaker back flushing - is she right?

As others note, it is important that the pre-filter for any fresh water from a shore supply that is used to flush the membrane must be the carbon type. I found some good info at

purewaterproducts.com/articles/carbon

regarding removal of chlorine and chloramines by carbon filtering.
waterman46 is offline   Reply With Quote
Old 14-03-2018, 22:25   #10
Marine Service Provider
 
SV THIRD DAY's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2006
Location: La Paz, Mexico
Boat: 1978 Hudson Force 50 Ketch
Posts: 3,859
Re: Watermaker back flushing - is she right?

Quote:
Originally Posted by mvmojo View Post
BTW, the pink antifreeze makes a good preservative for the membrane and keeps it from freezing. Sodium metabisulfite, the conventional preservative, does not appreciably lower the freezing point of water and therefore does not act as an antifreeze.
I live PG as a water maker pickling preservative!!!!
SV THIRD DAY is offline   Reply With Quote
Old 15-03-2018, 19:14   #11
Registered User

Join Date: Aug 2007
Location: Adelaide, South Australia, sailing in the Med.
Boat: Beneteau, Oceanis 50
Posts: 549
Re: Watermaker back flushing - is she right?

Quote:
Originally Posted by Renx View Post
Like me, you've probably spend countless hours wondering about carbon filters and back flushing your watermaker

I've been pondering a re-build of the basic pre-filter system on my 20 year old Dessalator Watermaker - see attached image - and working out the best way to add a carbon filter for back flushing.

Then in the middle of my complex circuit diagram my wife suggested just swapping out the string pre-filter for a carbon filter when doing the back flush from the water tank.

Please tell me this is a bad idea so I don't have to admit I've wasted countless hours and copious amounts of paper

Cheers..

Woody
@mothershipadrift
Ideally an additional filter housing for a dedicated carbon filter, but if too hard/no room, then a combination carbon/sediment filter cartridge.

Another way, of course is to only have RO water in your tanks - or filter through a carbon filter when filling at the dock. However then you have the potential issue of no chlorine/chloramine disinfectant in the tanks.

For us (also a Desalator), I use a combi cartridge in place of the regular string sediment cartridge. At some stage, with a bit of re-arranging I may find room for a second housing, but that's a future project. For the tank-water safety aspect, we use a Seagull filter under the galley sink for our drinking water. It is certified microbially safe, and the one airlines use, so good enough for us.
__________________

David B is offline   Reply With Quote
Reply

Tags
flushing, water, watermaker

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Does She Roll , Does She Wallow ? shipleft Powered Boats 16 18-04-2012 18:32
Which Catamaran is Right for You, Right for Me? betachz Multihull Sailboats 28 01-01-2009 10:23
no right way, right? unbusted67 Seamanship & Boat Handling 4 16-12-2006 18:10



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 23:35.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.