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Kemah, Texas
Watts Up! Marine Services has gone offshore and no longer provides local service. I have left this blog in tact for those that might find the information useful. I still monitor questions but only when internet is available.

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Sunday, January 9, 2011

Water Maker DIY - Part II

Today is the final post on the topic of reverse osmosis water maker systems.  In the previous post we discussed the systems needed to take water from the sea, pump it, filter it and then run it through the high pressure pump and RO membrane.  Today's topics will give more information on the things that are not usually seen: the things that keep everything running and doing what they are meant to do. 


Post RO
Automation/Controls
Automation is a convenience, but it is a convenience that I will not live without on the system that I would construct.  Yes, you could do everything manually, like changing valve positions, turning on pumps, and increasing or decreasing system pressures.  However, if you are going to have a water maker system that will last for many years to come, automation takes out some of the human error that is bound to occur.  


There are many different vendors supplying controls to run an RO water maker.  The determining factors are the amount of automation you want, the size of your water maker, the amount of power you have available and what you're willing to spend.  I am considering a Series 150 microprocessor controller made by R&D Specialties however there are numerous controllers available. Here is some information provided by HCTI:

Features:
•Economical compact package
•Liquid crystal display and multi-function keypad
•English or metric TDS and temperature values
•Visual and audible alarm, with alarm silence key
•Programmable time delays and set points
•Programmable flush mode
•Low pressure automatic reset
•NEMA 4X hinged enclosure
•Panel or frame mount
•Available with UL/CUL Listing
R&D Specialties, Series 150 RO Controller
Standard functions of the Series 150 controller are the monitoring and/or control of:
•RO high pressure pump motor
•Inlet solenoid valve
•Automatic flush solenoid valve
•Low feed pressure switch
•High pump pressure switch
•RO storage tank level switches (1 or 2)
•Permeate TDS/Conductivity
•Water temperature
•Pre-treat lockout
•Operating hours
•RO tank full override
 *TDS stands for Total Dissolved Solids 


Switch Inputs, Dry Contact:
• Pressure fault - low feed and/or high pump pressure
•Tank level high
•Tank level low
•Pickled treatment lockout
Relay Outputs:
•High pressure pump relay - 120/240V, 1 HP
•Inlet valve relay - 120/240V, 5 AMP
•Flush Valve relay - 120/240V, 5 AMP
•Relays supply same output voltage as board power (120 or 240V, VAC)



Valves/Water Control
I have seen numerous RO systems that have no automation and work very well, as long as the operator understands the system completely.  Knowing the water flow during each of the water making processes, start-up and fresh water flush can be difficult for someone that does not do this on a regular basis.   

In the system that I would design, complete automation is a requirement.  I want to be sure that anyone can operate the system even when I am not there to instruct.  Most good RO water maker controllers will have the inputs and outputs to control solenoid valves as needed.  The three way valves that will be used in this application will simply connect into the outputs on the controller.  Another function that would be handy, yet is not a must, is an automatic shut-off when the holding tanks are full.  Royce Industries makes an electronic level sensor that could be used to shut off the system when needed.  I know that I would often forget to monitor the water tank levels and it would be nice to know that the system is doing this for me.

Post Filtration
Post filtration such as carbon filters and pH neutralizers will simply help the flavor of the product water.  I feel it is a matter of preference rather than need.  In the system that I install, this will not be needed, yet could easily be installed at a later date if I so desire.  
UV Sterilizer
Ultraviolet Sterilizer
A U.V. sterilizer is recommended if the feed water (intake) is from a harbor, marina, or polluted source. The RO membrane rejects bacteria and viruses, however if biological migration occurs across the membrane, then the U.V. sterilizer will destroy 99.9 % of any biological intrusion in the product water.



Fresh Water Flush
Fresh water is required to flush or store the water maker.  Fresh water flush will greatly prolong the life of the reverse osmosis membrane elements by rinsing them with fresh water.  The fresh water flush will need to repeat itself every seven days.  By rinsing the water maker, salt water is displaced with fresh water within the RO system’s internal parts. This process will prevent corrosion of the internal parts and also reduce biological fouling of the membranes.

The fresh water used to flush the RO system is taken from the boat's pressurized fresh water system.  To ensure that chlorine does not enter the system, the pressurized water should go through a carbon filter first.  The carbon filter will remove any chlorine that might have entered the tanks when filling at the marina.
After the fresh water goes through the carbon filte,r it is a good idea to introduce it to the water maker at a “T” before or after the sediment filters.  If the fresh water is introduced before the sediment filters, it will offer additional protection to these filter cartridges.

According to one manufacturer of the RO membranes, membranes age as they sit unused. So delay the purchase of your membranes until after you finish installing the rest of the RO system and you are ready to use the system.

Pickling
The process of pickling, consists of adding a food preservative (sodium metabisulphite) to stop bacterial and fungal growth on the membranes and in the pressure vessel, is widely regarded as being effective for at least 3 months. I know of several RO systems on yachts that have been pickled for 1 year or more. One disadvantage to pickling is, the preservative leaves its mark on hoses (especially PVC), bronze fittings and stainless steel.  Given the option, I would prefer not to pickle the RO membranes but instead flush them frequently with unchlorinated fresh water.  The frequency of fresh water flush depends on ambient temperature: the warmer the temperatures, the more frequent a fresh water flush will be required.

Control automation is key to keeping the system clean and operational every time you will need it.  Many microprocessor controlled systems will give you the ability to program the frequency of fresh water flush.  Membranes can be pricy and forgetting to flush the membrane could result in added expense.  Water maker controllers can be a great insurance policy.

Ensuring that you have a properly functioning RO water system
Important things to DO: 
  1. Change the cartridge filters regularly. 
  2. Monitor the system and keep a log daily.
  3. Run the system, as much as possible, on a continuous basis.
  4. Pickle the system if you do not intend to operate for long periods.
Important things NOT to do:
  1. Permit chlorine in the feed water.
  2. Shut down the system for extended periods without pickling.
  3. Close the throttle (pressure) valve completely.
  4. Operate the system with insufficient feed flow.
  5. Allow the membrane to become dry. 
Water Temperature - How does this affect the operation?
Temperature of the feed water can affect the water maker's ability or inability to make fresh water.  As the temperature of the feed water drops, so will the fresh water production.  As the temperature of the feed water increases, the fresh water production should also increase.  With this known, a decrease in feed water temperature can be compensated by increasing the feed pressure up to the maximum allowed by the membrane, pump and associated components.  Once the maximum pressure is reached, a further decreasing temperature causes the permeate flow to decrease and nothing more can be done.  Increasing temperature is compensated by lowering the feed pressure.

Seawater/brackish water operation-What might we change?
Feed water salinity can also affect the water maker’s ability and efficiency.  An increase in the feed water salinity can be compensated by increasing the feed pressure up to the maximum. If further pressure increase is not possible, than a lowered permeate flow and system recovery has to be accepted.  A lower feed water salinity, such as the brackish bay water, allows us to decrease the feed pressure and continue to receive the same product water flow.


Budget
Now for the most important information of this series, the cost!  Currently the costs for the major components are listed below, however there are additional costs for all the minor components that I have factored into my budget.  When looking at a good water maker system, the costs will be $7,000-$10,000 for a pre-constructed system that will produce more than 100-150 gallons in a day, I think I will easily be able to do better than that.  Here are the items that will put the biggest dent in your checkbook. 
  • Low pressure feed pump     - $250
  • High pressure RO pump      - $750
  • High pressure pump motor - $250
  • High pressure vessel            - $350
  • RO membrane                      - $200
  • RO Controller                       - Awaiting pricing information
So that's it in a nutshell (in three posts!). Water makers mystify a lot of people, but they are really very simple filtration systems once you wrap your brain around exactly how they work. Questions?  Hit me. I'll be happy to answer any questions you might have about your unique situation.

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