Valves for Desalination Plants: Types, Applications and Certifications

A seawater intake, an initial filtration, high-pressure pumping, the membranes. Then energy recovery and post-treatment. Before it becomes fresh water, seawater passes through a sequence of phases, and in each one the fluid must be controlled.

The process is called desalination, or desalinization: the removal of dissolved salts from water, particularly from brackish water and seawater, to obtain fresh water for civil and industrial use. In desalination plants for civil use and in industrial desalination equipment, one of the main technologies is reverse osmosis, which, when applied to seawater, is known as SWRO (Seawater Reverse Osmosis).

In desalination plants, therefore, valves do not work at a single point of the line: they follow the water from inlet to outlet, together with the actuators that operate them and the automation accessories.

Types of valves for desalination plants

OMAL desalination valves include one butterfly valve and three series of ball valves, all of which can be automated with our pneumatic valve actuators.

KRAVEN is the butterfly valve, available in wafer and lug versions with PN and ANSI flanges, from DN40 to DN300, with a cast iron body and EPDM, NBR and FKM seals. Among the ball valves, MAGNUM Split Wafer is a full-bore wafer ball valve, from DN15 to DN200, which reaches PN 63-100 and ANSI 600 up to DN100.

THOR Split Body is the flanged ball valve for the highest pressures: from DN15 to DN25 it reaches ANSI 900-1500, which makes it the high pressure ball valve of the range. ITEM 424, on the other hand, is a three-piece stainless steel ball valve, up to PN 63, with an actuator mounting flange compliant with ISO 5211.

On the automation side, AGO actuators are scotch yoke pneumatic actuators in aluminum, from 8 to 8,000 Nm in double-acting versions, also available with an integrated handwheel and with epoxy coating. Heavy Duty actuators, in carbon steel, reach 32,000 Nm. Limit switch boxes, positioners and manual gearboxes complete the series.

The six phases of reverse osmosis desalination plants

In reverse osmosis plants that treat seawater, the desalination process comprises six main phases, all covered by OMAL solutions:

●      Seawater intake: water is drawn in through submerged pipes or coastal wells.

●      Pretreatment: an initial filtration removes suspended solids, sand and algae.

●      High-pressure pumping: water reaches the pressure required to pass through the membranes.

●      Reverse osmosis: the membranes retain salts, bacteria and impurities and separate fresh water from brine.

●      Energy recovery: the hydraulic energy of the outgoing brine is reused to reduce energy consumption.

●      Post-treatment: the water is remineralized and disinfected before distribution.

 Reverse osmosis, including industrial reverse osmosis, therefore does not end at the membranes: in a seawater desalination plant, fluid control involves every step of the line.

Certifications for valves and actuators

The certifications available across the OMAL range vary from product to product and include Ex CE/UKCA, Pressure Equipment CE/UKCA, SIL up to SIL3, TA Luft & Fugitive Emission, Fire Safe and IECEx. They concern the individual component and the selected version, not the desalination process.

Why a single partner for valves, actuators and accessories

Anyone designing or managing a desalination plant has to choose valves, actuators and accessories for several phases of the line. Relying on a single partner changes the work on three fronts.

The first concerns points of contact. The OMAL range covers the main phases of the SWRO process, from seawater intake to post-treatment, with a single reference for both the valve (which concerns the process) and the actuator (which handles its automation).

The second concerns production. Specialized in valves and actuators since 1981, OMAL designs and manufactures both components in the same facility: it keeps their technical characteristics under control and supplies a valve-actuator package that is already coupled and sized, with the actuator selected based on the torque required by each valve.

The third concerns management. Reducing the number of suppliers simplifies three stages of the work: selection, which takes place within a single range of valves, actuators and accessories; automation, because the valve and actuator are supplied already matched; and the management of components in operation, which is handled by a single point of contact.

Want to learn more about the complete range of valves and actuators for desalination plants? Click here and discover OMAL solutions.

FAQ: frequently asked questions about desalination and valves for desalination plants

Seawater desalination: how does a desalination plant work with reverse osmosis?

Water is forced at high pressure through membranes that retain dissolved salts, bacteria and impurities, separating fresh water from brine. The complete process comprises six main phases: seawater intake, pretreatment, high-pressure pumping, reverse osmosis, brine energy recovery and post-treatment, with remineralization and disinfection before distribution.

What is desalination brine?

It is the stream that contains the salts retained by the membranes, separated from fresh water during reverse osmosis. In SWRO plants it leaves the membranes at high pressure: its hydraulic energy is recovered and reused to reduce energy consumption.

Which valves are used in desalination plants?

The OMAL range of desalination valves includes one butterfly valve and three series of ball valves. KRAVEN is the wafer and lug butterfly valve, from DN40 to DN300. MAGNUM Split Wafer is the wafer ball valve, up to ANSI 600. THOR Split Body is the flanged ball valve for the highest pressures, up to ANSI 900-1500. ITEM 424 is the three-piece stainless steel ball valve, up to PN 63.

How are valves automated in an SWRO plant?

In the OMAL range, valves are automated with quarter-turn pneumatic actuators. AGO scotch yoke actuators in aluminum range from 8 to 8,000 Nm in double-acting versions and from 15 to 4,000 Nm in spring-return versions. They are also available with an integrated handwheel, to operate the valve when the compressed air is disconnected, and with epoxy coating. For higher torques, Heavy Duty actuators in carbon steel reach 32,000 Nm. Limit switch boxes, positioners (pneumatic, electro pneumatic and smart HART) and manual handwheel gearboxes complete the automation.

What certifications do valves and actuators for desalination have?

Depending on the model, OMAL valves, actuators and accessories can be certified Ex CE/UKCA, Pressure Equipment CE/UKCA, SIL up to SIL3, TA Luft & Fugitive Emission, Fire Safe and IECEx. These certifications relate to the individual component and the selected version, not to the desalination process.