Why do marine watermakers consume power, and how does the SPECTRA Clark Pump recover pressure?
When looking to turn seawater into daily drinking water on a boat, water production capacity is certainly important, but what truly dictates whether a system can operate for long periods is power consumption. Reverse osmosis (RO) watermakers must first pressurize the seawater, a demand that must be borne by the boat's batteries, generator, solar, or wind power systems.
The point of the SPECTRA Clark Pump is not to eliminate the need for high pressure in reverse osmosis, but to recover the pressure that would otherwise be discharged with the brine and transfer it to the incoming seawater, thereby reducing the electricity required to re-pressurize each cycle.
Four key points to master:
- Seawater reverse osmosis requires high pressure, and the primary power consumption occurs during the pressurization process.
- Brine still holds pressure when it leaves the RO membrane; if discharged directly, this energy is lost.
- The Clark Pump transfers the brine's pressure to incoming seawater, reducing the load on the external feed pump.
- According to manufacturer data, specific systems utilizing energy recovery designs can reduce energy consumption by up to approximately 75% compared to conventional RO watermakers.
Where is energy wasted in conventional watermakers?
Reverse osmosis (RO) does not rely solely on filter media to push seawater through. The system must first pressurize the seawater, allowing a portion of water molecules to pass through the RO membrane to become fresh water; the water that does not pass through is discharged with a higher concentration of salt.
The problem is that this brine still carries pressure when it leaves the membrane housing. If a conventional system discharges it directly back into the sea, the energy previously used to pressurize it is lost along with it; the high-pressure pump must then rebuild that pressure for the next cycle, increasing electricity demand.
How does the Clark Pump recover pressure?
SPECTRA introduced the Clark Pump in 1997. It is a hydraulic intensifier and energy recovery device that uses the pressure of the brine—which would otherwise be discharged—to drive an internal piston, which then transfers that pressure to incoming seawater.
- Low-pressure supply: The feed pump first sends pre-filtered seawater into the system.
- Reverse osmosis separation: Seawater enters the membrane housing under pressure, where it is separated into fresh water and brine.
- Pressure recovery: Pressurized brine enters the Clark Pump and pushes the piston.
- Transfer to incoming seawater: The piston transfers the recovered pressure to the next batch of incoming water in a cyclical operation.
Simply put, the Clark Pump recovers the pressure of the brine, not the discharged brine itself for drinking. Reverse osmosis still requires high pressure; it's just that the external pump no longer has to handle all the pressurization work on its own.
How should "up to approximately 75% energy reduction" be interpreted?
According to SPECTRA's manufacturer data, specific systems using the Clark Pump can reduce energy use by up to approximately 75% compared to conventional high-pressure pump architectures. The key words here are "up to" and "compared to conventional systems."
This is not a fixed figure for all models and environments, nor does it equal "75% increased efficiency." Actual power consumption is influenced by the model, water production volume, seawater temperature and salinity, power supply configuration, intake conditions, and equipment status; you should always refer to the official manufacturer specifications for each model.
Back on board, what is the practical difference of low power consumption?
A boat's electricity must supply navigation, communication, lighting, refrigeration, and other household equipment simultaneously. The less power a watermaker requires, the easier it is to integrate into the boat's overall energy plan, and it reduces the load when the watermaker runs concurrently with other equipment.
Low-power design also allows some systems to potentially run on batteries, solar, or wind power. However, whether this is actually feasible depends on the model's power rating, daily operating hours, battery capacity, and power generation; it shouldn't be assumed simply based on the phrase "can be used with renewable energy."
When choosing a watermaker, don't just look at energy-saving percentages
The Clark Pump solves the issue of energy recovery, but whether a watermaker system is suitable must return to the boat's practical conditions:
- Daily water demand: The number of people on board, the length of the voyage, and daily consumption habits determine the necessary water production capacity.
- Available power: Confirm voltage, model power rating, battery capacity, and how much power solar, wind, or generators can provide.
- Installation and maintenance space: Beyond the unit's dimensions, you must reserve space for plumbing, pre-filters, flushing, and replacing consumables.
- Raw water conditions: Water temperature, salinity, and water quality can all impact actual water production and system performance.
- Maintenance and backup: Confirm availability of consumables, cleaning requirements, and maintenance conditions; for long voyages, keep a necessary reserve of backup fresh water.
For higher flow requirements, SPECTRA also offers energy recovery systems using the Pearson Pump. The Clark Pump and Pearson Pump are not distinguished by tier, but by their suitability for different flow rates and system configurations; choice should be based on actual water requirements, power supply, and installation conditions.
Want to learn more about SPECTRA water systems
To further understand the differences between the Clark Pump and the Pearson Pump, you can read the full technical explanation from KATADYN Taiwan; if you are already evaluating marine watermakers, you can proceed to compare the water production, power, and installation requirements of each SPECTRA series.
Sources: SPECTRA Watermakers "Our Technology", FAQs, and marine watermaker manufacturer manuals; Katadyn Group SPECTRA branding and technical materials.
