Service Prefilter Alarm (systems WITH boost pump) - SPECTRA CONNECT
During normal operation, the feed water is filtered in two stages. First, it enters a fine mesh metal sea strainer then passes through a boost pump. This protects the boost pump from damage. After passing through the boost pump the feed water enters the filter housings containing 20 and 5 micron elements. These filters remove very fine particles which could damage the Feed Pump or Clark pump, and which would shorten membrane life. Some systems will only have a 5 micron filter. Service schedules will vary widely depending on how and where the system is used. If large amounts of feed water are run through the system in a relatively short period in biologically fertile near shore waters, the prefilters will plug up, the pressure drop across the filters will rise, product production and quality will drop, and the system will sense plugged filters and give a SERVICE PREFILTERS alarm.
Here is a simplified look at how your system reads filter condition:
- The boost pump pushes water through the filters and to the inlet of the pump. Here there is an absolute pressure sensor that serves as the "boost pressure sensor" (yellow).
- When the prefilters are calibrated (with clean filters) the system recognizes this pressure as a 'clean pressure'. When the boost pressure reads the clean pressure, filter condition/life is 100%
- As the filters get clogged with dirt and debris the pressure on the outlet of them goes down and the filter condition goes down.
- The 0% filter condition is when the boost pressure reads 10 psi. This is when the filters are so clogged and the pressure is so low that the pump feed pump is sucking an unhealthy amount (roughly 5 psi or so below atmospheric pressure)
When the system is on the sensor should be reading a value around the 12 – 20 range, anything below 10 will trigger the alarm. The service prefilter alarm on your system can be triggered by anything causing a flow restriction/pressure drop between your feed pump and the ocean. Obviously the prefilter is one option but others worth looking into are:
- Black sea strainer inlet check valve clogged with debris*
- Clogged through hull
- Sea strainer screen
- Kinked or leaking hose
- Boost pump weak, off, or receiving less than 24V (Boost Pump Test)
For Spectra Connect systems the Prefilter Fault is programmed via 'Calibrate Prefilters' as well as the 'Low Vacuum Limit'. To recap, default low vacuum limit is roughly 5psi below atmospheric pressure. If you lower this value (minimum 8psi), you are increasing the strain on your feed pump head for potential damage, though you will get longer intervals between filter changes.
Refer to your owner's manual for calibration steps. For proper prefilter calibration, ensure you have a BRAND NEW set of prefilter elements installed and are in clear open-ocean water. When you recalibrate your filter condition, you are telling the system to capture a reading of normal inlet feed pressure with brand new, clean filters installed. This sets the 'clean pressure' value. Doing this with dirty or even slightly dirty prefilters will throw off its filter condition accuracy. The Spectra Connect will alarm 'Service Prefilters' when it notices the boost pressure drop from the clean pressure with new prefitlers to below the low vacuum limit (default 10psi).
LOW VACUUM LIMIT: Set point for the maximum allowable pressure drop through the prefilter. If the inlet pressure reading drops below this point the unit will alarm “Service Prefilter” and shut down. This set point is in absolute pressure, and determines the “Replace” end of the Prefilter Condition bar graph. In most cases this parameter should be set to 10.
------------- If you are seeing Service Prefilter when you freshwater flush your system, see this link for help -----------------