The Clark Pump is the heart of the Spectra Reverse Osmosis Watermaker. It is a
high tolerance, precision machine, developed after thousands of hours of operation and
testing. Troubleshooting, repair and rebuild of this machine may be undertaken by any
mechanically-minded technician or boat owner. A willingness to understand the process,
acute attention to detail, a clean work area, and careful reading of the instructions are
absolutely necessary! One dirty or out of place part could render the Clark Pump
inoperable.
Refer to the Function Diagram on page 5. The Clark Pump uses two opposing
cylinders with pistons that share a single rod that passes through a center block. A reversing
valve, controlled by a pilot valve that is mechanically actuated by the pistons, allows the
cylinders to alternate between driving and pressurizing. The driving cylinder has feed
pressure pushing on the top of the piston. The driving piston pushes the rod through the
center block. The water under the driving piston (brine), that has gone through the
membrane on the previous stroke, is discharged overboard. A cylinder starts to pressurize
when the rod is forced into it. As the rod pushes the driven piston, it circulates the water on
top of the piston through the membrane, back to the reversing valve, which directs it back
into the same cylinder under the driven piston where the rod is entering. This creates a
closed loop between the cylinder and membrane. The rod displaces water as it enters the
cylinder and since the displaced water at this point has no place to go, the pressure instantly
rises until there is enough pressure for reverse osmosis to occur in the membrane, allowing
the displaced water to be forced out as product. Thus fresh (displaced) water equal to the
volume of the rod entering the cylinder is produced on every stroke as the piston circulates
the water through the membrane. When the driven piston bottoms out on the center block, it
actuates the pilot valve and the process is instantly reversed.
Another perspective on the Clark Pump is that it is two devices combined into one.
The two opposing cylinders that share a single rod take turns being a “hydraulic ram,”
driving the rod into the “circulating pressure intensifier.”
Differences in the flow and pressure gauge readings between “shifts” of the Clark
Pump (asymmetry) indicate that something is different between the two cylinders. For
example, if the right piston seal begins to leak, it would affect the readings when the right
cylinder is working hard trying to push the rod into the other cylinder but would have no
visible affect as the right cylinder is pressurizing after the “shift.”
On earlier units, a button is provided on the reversing valve to reset the reversing
valve if the pilot and the main valves stop at dead center.
Having a good working knowledge of the Clark Pump’s internal functions greatly
enhances troubleshooting and repair.
If a problem arises, consult the technical bulletins, note the symptoms and call
Spectra Watermakers or e-mail techsupport@spectrawatermakers.com before
disassembly.
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