Low product flow with high feed pressure is commonly caused by clogged up membranes and/or prefilters. However, in rare instances, some 700 and 1000 model watermakers may exhibit these symptoms due to “tight pistons”. The pistons and/or the piston bushings, can swell slightly especially in very warm waters which will cause the piston assembly to expand inside the cylinder, slowing the Clark Pump and causing the feed pressures to rise and production to fall. In most cases the system will also be erratic, operating normally for a time and then shutting down on “System Stalled” or “High Pressure” and/or showing varying system pressures.
If you have a high-pressure or stall fault it would help to know a few pressure values while the system is running in Run Manual. When the system is running via the Run Manual toggle switch you are directly supplying power to your motor and bypassing all electronic controls. If you access the programming section of the display when the system is in Run-Manual you can view the real-time readings of the system as outlined in the programming from the display section of the user manual. Follow the steps below to assess your system for 'Tight Pistons'.
- Open seacock and get ready to make water
- Open the pressure relief valve on the Clark Pump 2 full turns
- Move the toggle switch to Run Manual.
- Confirm that pump sounds smooth (not cavitating) and that water is discharging overboard
- Enter the programming mode: Programming From Display (MPC)
- Tap the ALARM/DISPLAY button until you see ‘Pressure Limit’ or ‘Outlet Offset’, both have a real-time pressure reading in the top left-hand corner of the screen
- Note the outlet pressure reading.
- On systems without “tight pistons” this will reading should be below 65 psi or 4.5 bar
- If any screen is left for alone for more than 30 seconds the system will leave program mode.
- Close the pressure relief valve on the Clark Pump 1.5 turns (1/2 turn from fully closed)
- Note the real-time outlet pressure reading (left-hand reading on ‘Pressure Limit’ or ‘Outlet offset’ window).
- On systems without “tight pistons” this will reading should be around 80 psi or 5.5 bar
- Close the pressure relief valve all the way
- Note the real-time outlet pressure reading (left-hand reading on ‘Pressure Limit’ or ‘Outlet offset’ window).
- On systems without “tight pistons” this will reading should be around 165 psi or 11.6 bar
If your pressure readings were higher than they should be, it would be worth examining your pistons and potentially shaving the bushings down with a sharp blade. Below is this procedure outlined.
To fully diagnose this problem remove the cylinders from the center block. Remove the end caps and J-tubes (by loosening the nuts on the high pressure fittings and remove the J tube as an assembly). Push on each of the pistons with the handle of a hammer (or a wood stick), they should take quite a bit of force to move but you shouldn’t need drive the pistons out using the wooden stick and a mallet. If they are that tight then you have “tight pistons”. You can use the above method to test out without having to dismantle your Clark Pump.