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Best Reverse Osmosis Water Storage Options for Combi Ovens

Many of you out there are considering utilizing reverse osmosis systems to protect your combi ovens or improve your coffee beverage. R.O. Systems are used to remove dissolved solids and impurities in your water supply by forcing water through a semipermeable membrane. However, the process of reverse osmosis filtration is a slow one and as such requires a good storage tank to keep your purified water stored in. So let’s look at a few of the choices that are available as tanks and show you which ones may be better for your situation.

Hydro-pneumatic storage tanks - are the most common style tanks for home and well water systems. This tank has a rubber bladder in the middle of the tank with an air charge on one side of the bladder and filtered water on the other side of the bladder.  As the water is forced into the water tank the air on the other side of the bladder is compressed increasing pressure to the system. When a valve downstream from the tank is opened the compressed air pushes the water out of the tank and on to the equipment. As the water empties, the air on the other side of the bladder becomes less compressed reducing the pressure of the tank.

For example: Generally, a combi oven requires at least 30-40 psi feed-water pressure to operate without alarms. If your feed-water pressure to the R.O. System is 40 psi, the bladder tank will only fill to 27-30 psi when full.  Therefore, when the oven calls for the first ounce of water from the tank the oven will alarm due to inadequate water flow and shut-down due to having inadequate pressure feeding the oven.

Advantages of Hydro-Pneumatic Storage Tanks

  • No electricity required
  • Easy installation
  • Quiet operation
  • Sealed from ambient conditions

Disadvantages of Hydro-Pneumatic Storage Tanks

  • Requires periodic refilling of air pre-charge
  • Traps concentrated CO2 and dissolved oxygen in stored water
  • Creates back-pressure on filter, reducing production rate
  • Maximum pressure from the tank is lower than feed water pressure
  • Inconsistent output pressure and flow to downstream equipment

Due to the constant change in water pressure by the hydro-pneumatic storage tank and the increase in dissolved CO2, OptiPure does not recommend this tank for combi ovens and espresso machines, as the change in pressure and CO2 concentrations may negatively impact your equipment performance.

Atmospheric Storage tanks are generally made of food-grade polyethylene and can be molded in almost any size and shape. The filtered water is stored passively in the tank and must be re-pressurized by an electric pump every time water is drawn from it. The reverse osmosis system is controlled by a float switch or float valve in the tank to shut off water supply. An atmospheric tank is open to the ambient conditions in the restaurant so it is necessary to have a sealed lid and a sub-micron air breather to prevent grease, mold, fungus, and yeast from entering the tank.

Advantages of Atmospheric RO Water Storage Tanks with RP Pump

  • No back pressure from tank increasing RO water production
  • Vented to atmosphere allowing concentrated CO2 and dissolved oxygen to outgas
  • Pump maintains a consistent pressure and flow throughout the entire tank volume
  • Smaller tank volume due to no bladder and air-charge
  • No need to recharge air charge
  • Output pressure is independent of feed-water pressure
  • Output pressure can be higher than feed-water pressure

Disadvantages of Atmospheric RO Water Storage Tanks with RP

  • Requires electricity
  • Pump eventually needs repair or replacement
  • Sub-micron air breather needs replacement

In Conclusion

Due to the flow and pressure requirements of today's boiler-less combi ovens and espresso machines, OptiPure generally recommends atmospheric tanks with re-pressurization pumps to meet manufacturer specifications. However, in some low-volume, space-constrained, espresso machine applications a small bladder tank is the better option. They can be used if the espresso machine is not sensitive to variations in water pressure and the water chemistry is compatible.

The Hydro-pneumatic storage tank is more useful for small-scale espresso machines and steam-cooking equipment that do not require constant pressure or water conditions.

The atmospheric RO water storage tank is more useful for restaurant applications that require constant pressure and water conditions for their espresso and combi ovens.

For more details about proper R.O. System selection and application for your combi oven or espresso machine contact the experts at OptiPure.


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