Pure Rinse Window Cleaning Reverse Osmosis System
The following is an explanation of the design concept for Pure Rinse R.O. systems that we use to clean windows and solar panels
Pure Rinse systems have oversized, triple pre-filtration housings and cartridges. The first cartridge is a five micron sediment filter. The second is an optional long life mixed media carbon cartridge or the standard carbon block cartridge to remove chlorine. The carbon cartridge protects the R.O. TFC (Thin Film Composite) membrane. Chlorine is very destructive to TFC membranes. The third cartridge is a one-micron final filter to remove remaining “fines”.
Triple pre-filtration increases initial price of our system. However, it reduces maintenance, operating cost and downtime. Payback for this incremental initial cost is less than one year or the first time you stop in the middle of a job to replace undersized cartridges.
The first filter, the five-micron cartridge, in the lowest cost filter and is replaced most often. Just how often is determined by the condition of the water. Gauges are provided to monitor pressure drop of water flowing through the filter. If water pressure coming out of the filter is 0-10 PSI less than water pressure entering the filter, then the filter is in good condition. If pressure drop is greater than 10 PSI, then replace the filter cartridge. These measurements are taken with unit running. When unit is not running all gauges should be exactly equal. If all gauges are not equal consider replacement.
The second filter is an optional mixed media carbon filter or our standard carbon block filter. Its function is to remove chlorine. Chlorine attacks TFC R.O. membranes. Mixed media carbon filter cartridges are four times more expensive than carbon block cartridges but last 10 times longer. There is no simple recommended service interval. For example, if you use well water with no chlorine you may never need replacement. If you are in an area of high chlorine content you should consider changing the carbon block cartridge every 1000 gallons or the mixed media cartridge every 10,000 gallons. Annual replacement, under normal conditions, is usually an adequate service interval.
The third filter is a one-micron final filter. It removes remaining sediment not removed by the five micron filter and carbon fines released by the carbon filter. Again, if pressure drop exceeds 10 PSI the filter cartridge should be replaced.
Filter cartridge replacement is completely determined by local water conditions.
A service interval for bad water (high chlorine and high TDS) areas might be:
Five micron pre-filter cartridge: replace at 10 hours running time
One micron final filter cartridge: replace at 20 hours running time
Carbon block cartridge: replace at 10 hours running time
Carbon mixed media cartridge: replace at 100 hours running time
Ten hours running time equals 1500 gallons of source water flowing through the pre-filtration system.
With our triple banked system, under ideal conditions, 70% of the 1500 gallons will be pure water, or approximately 1000 gallons.
A 50 gallon tank would be filled 20 times with 1000 gallons.
Well water has no chlorine. Therefore, carbon cartridges last a very long time. However, well water has high levels of sediment. Therefore, replacement of the 5 micron cartridge is required more often when using well water.
Pure Rinse has selected HR (High Rejection) membranes for their system rather than HF (High Flow) membranes.
HR membranes run at higher pressure (150-200 PSI), produce less wastewater and have a 98-99% rejection rate. For example, if source water TDS (Total dissolved solids in parts per million) is 500 then the product water (pure water) out of the HR R.O. membrane would be 10 or less TDS (2% or less of 500 TDS). “SPOT FREE” rinsing requires TDS to be 10 or less.
In contrast, HF membranes run at low pressure (20-80 PSI) and have only a 90% rejection rate. Again, for example, if source water is 500 TDS then the product water (pure water) out of the HF membrane is 50 TDS (10% or less of 500 TDS). The advantage of the HF membrane system is it can operate with tap water pressure in areas with high tap water pressure (50 PSI or more). City water pressure is usually adequate, well water pressure is usually inadequate.
HF (high flow) membrane systems have several disadvantages:
1.) They require a secondary D.I. system to remove the higher residual TDS.
Residual TDS is ten times higher than that of HR (high rejection) systems.
2.) They rely on local water pressure to be above 50 PSI. Well water is usually 20-40 PSI.
3.) They use three times more water to produce pure water. This is because they are single pass systems and use the source water only once.
4.) They create more waste water. Manufacturers of membranes require 80% of source water flow to become waste water to avoid fouling and premature failure.
5.) The membrane fouls and needs replacement more often.
6.) They require three times the service and replacement of filter cartridges. The triple banked Pure Rinse HR system uses the source water three times, only 30% of source water flow becomes waste water.
The Pure Rinse HR membrane has a 98-99% rejection rate (reduces TDS to 1 or 2% incoming water). In areas where local water conditions are 500 TDS or lower no D.I. final “polishing” of pure water is required. In areas where TDS in greater than 500, we recommend our “polishing” attachment, “THE ZERO”. This is an optional D.I. cartridge in a filter housing to be used, as required, in areas of high TDS water.
“THE ZERO” polishing attachment is a simple and relatively low cost alternative to using D.I. tanks that are required with the HF membrane system.
Remember, the HF (High Flow), membrane leaves 10 times the residual TDS than the HR (High rejection) membrane. The service life of the final “polishing” D.I. cartridge in the HR system will last ten times longer than a D.I. cartridge in the HF system. Again, the HR system has only 1/10 the residual TDS of the HF system.
For example, the capacity of our D.I. polishing cartridge is 18,000 TDS. If incoming water to the D.I. Cartridge has a TDS of 10, the cartridge would be good for 1800 gallons. If incoming water to the D.I. Cartridge is 100, the cartridge would only be good for 180 gallons.
D.I. tanks are expensive, bulky and a nuisance. Frequent replacement of D.I. cartridges is also expensive.
HR systems have a substantial operating cost advantage and are more reliable.