Cat Pumps

Selecting a pump for sea water reverse osmosis


Courtesy of Cat Pumps

Reverse osmosis (RO) desalination has become a significant process used in the purification of water. Selecting the correct pump is a significant step in a well designed and properly operating pumping system. Although the pump is a relatively small part of the overall cost of an RO system, expenses resulting from downtime and inefficiency can quickly diminish the productivity of the RO system and your return on investment. Due to the corrosive atmosphere and high demands on these sea water RO systems, special attention is required in the pump selection process. There are several key factors that will help to ensure optimum RO pump and system performance.

Pump Compatibility

Pump compatibility is a key element in the selection process. Due to the fact that seawater is a corrosive liquid, containing a variety of microorganisms and the water temperature may vary, the materials of construction of your RO pump are critical. Some installations and water conditions may tolerate a liquid-end construction of nickel aluminum bronze. Other locations may demand more corrosion-resistant liquid-end materials such as 316SS, Duplex Stainless Steel or even Super Duplex for the RO pump. Each installation must be reviewed on its own merits, but having these RO pump options will assure the best fit to the installation.

Pump Efficiency

RO Pump efficiency is a key element in keeping the costs of providing fresh water at an affordable price. Generally, positive displacement (PD) plunger pumps operate with 85-95 percent overall efficiency, while centrifugal pumps are between 30-60 percent efficient. With the lower efficiency pumps, the addition of an energy recovery system is required to boost the efficiency. It is possible to add these energy recovery systems to the higher efficiency PD pumps to achieve maximum output and return on your reverse osmosis system investment.

Pump Speed

A lower speed (rpm) for your RO pumps is highly recommended. When pumping corrosive liquids such as seawater, higher rpm operation further aggravates the corrosion-erosion wear process initiated by seawater. Lower rpm pumps also help to reduce the risk of cavitation.

Ease of Installation

Easy and compact installation is a consideration. Many RO systems are on board cruise ships, naval vessels, freighters, off shore platforms or at hotels and resorts. Space and weight are two primary considerations in selecting your RO pump. Convenient, easy connection of inlet and discharge plumbing is preferred.

Installation is easier when system accessories conveniently attach to the pump head or immediately in the inlet and discharge lines. This minimizes delays in valve response time and facilitates periodic visual checks of the system performance. The RO pump should be fitted with a booster pump when seawater is lifted from a well or through the ship hull valve or sea chest to assure adequate supply of liquid to the pumping chambers.

System Accessories

RO system accessories are nearly as important as the RO pump itself. Each system requires accessories to set system pressure, by-pass when pumped liquid is not required and protect from possible overpressure. Without proper pressure relief installed in the system, the RO pump is subject to deadhead and destruction should the RO system fail or become blocked. Pulsation is damaging to the RO membranes. A pulsation dampener will minimize pulsation and prolong the life of the entire system. A suction stabilizer or captive acceleration tube [C.A.T.] will stabilize inlet pump pressure. An exclusive of CAT PUMPS®, the C.A.T. will minimize the inlet pulsations and reduce the risk of cavitation in the RO pump. A pressure gauge is essential in the all pump systems as a monitor of system performance. As soon as pressure drops or begins to fluctuate, a maintenance inspection should take place. Prolonged operation with worn components can result in more serious and costly repairs.

Service and Support

Pump serviceability is a significant factor in selecting an RO pump. Delivering fresh water requires a continuous-duty system and downtime is not tolerated. Periodic maintenance should be minimal, easy to perform and require few tools. Easily removed pump valves and seals, and replaceable heads are preferred. Good technical support and readily available parts are essential.

Selecting a manufacturer that can technically support your RO pump once it's in operation is not only a comfort, but a necessity. Knowing your pump can be serviced within 24 hours anywhere around the world is a benefit for you and your reverse osmosis system.

Proven Dependable

Dependability is an absolute necessity. RO seawater desalination is an application where a supplier's reputation for dependability weighs heavily in the selection process. With lives and livelihoods depending on fresh water delivered by your RO system, you do not want to be experimenting with an unproven pump. You will want to select a pump manufacturer who has experience with reverse osmosis desalination and has a history of dependable pump performance.

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