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[Article Title]Optional features in RO system design
[Artical Suimmary] They may not be critical, but they can save much time and expense.
[Article Contect]

^{Optional features for a reverse osmosis (RO) system become a type of wish list. Dealers (or their customers) may say, i wish I could have all the bells and whistles on the unit, but I don’t want to pay the added cost.?br>
However, although they add cost, a few such features add value and save RO system maintenance time and expense. Here are features I clearly would not overlook and always include:}

• Flowmeters. Last month, we determined that pressure is a byproduct of flow, and how can we determine flow without flowmeters? How many times have you tried to fill a bucket while timing it to determine flows (and got yourself and the area soaked)? Not having flowmeters is like driving your car at night without the headlights on ?it doesn’t make sense.
• Low-pressure protection. What will it cost you in lost time to replace that high-pressure pump that ran without feedwater, even if it is covered under warranty?
• Pressure gauges. You know what the flow is, but do you know if it is causing the pressure to be too low or too high? If you think of the membrane as a valve, with one side at high pressure and the other at low pressure, as the membrane loads and becomes fouled, the inlet pressure increases. As that pressure increases, the pump puts out less water. Now you have less water flow, so membrane fouling worsens, and you get higher pressure on the inlet feed and the membrane housing. (What are their pressure ratings?)

It’s a good idea to put pressure gauges before each piece of equipment preceding the RO, as well as before and after the 5-micron prefilter, after the high-pressure pump, and before the membrane inlet (inter-stage if applicable) and the concentrate.

The permeate should have a pressure gauge if the distribution is a direct feed (as opposed to stored feed). If the product water goes to storage, you typically can do without a pressure gauge at this position in the system, unless the pipe runs to storage are excessive (above 10 feet).

Other helpful features
Other features to be considered but not required all the time in an RO system are:

• TDS meter. This allows you to see the performance and rejection of the membrane, but it is not essential to the operational functions. You can achieve the same results with a good-quality handheld unit that you can take from place to place.
• Auto-fast-flush. This is an excellent feature if you have a system that is only on line for short periods or in a home that is used for vacationing and occupied part of the time.

The flush feature will allow the RO to run about 5 minutes every 12 hours to remove stagnant water and wash the membrane with feedwater. It is also a good option in situations where the feedwater is questionable or has hydrogen sulfide.

The H₂S issue
Unlike iron or hardness that can be filtered or ionically exchanged, hydrogen sulfide (H₂S) is a gas, and as a gas it will typically pass through the membrane without harm.

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