How soon after the WFP came on line did the IT occur?
So many times it has been observed that the WFP has been in “pause”, as programmed to do, during the same 24 hour timeframe that an IT ( integrity test) is scheduled to automatically occur on a specific module unit. The interrupted IT schedule is held in waiting until the filtration process “wakes up” and flow begins. Upon plant startup, any unfinished tasks, such as the programmed IT’s, are immediately initiated by the PLC.
Experience has shown that when the WFP comes out of “stand-by” or “pause” mode, the process does not have to stabilize before the PLC initiates the scheduled IT. Invariably, an IT initiated at plant startup has not produced reliable results and fails the IT 99% of the time. We have found that disabling the IT process until “daylight” or normal working hours and allowing the process to run for at least 45 minutes to an hour produces IT’s that have more meaning and the operators’ full attention. For example: We have had IT’s occur at 2 am in the morning and a module unit has a critical shutdown alarm from a high IT! Why did the IT fail? This is hardly the time to begin troubleshooting, so we would isolate the module unit for the night and take care of the problem in the morning.
The IT Won’t Latch – Symptoms
- Air pressure keeps escaping not allowing the rack to start the actual Integrity test. (IT) (the IT countdown timer will not stabilize for 1 minute, keeps resetting)
- You physically observe air bubbling in the clear upper coupling on the modules from the fibers.
The IT Won’t Latch – Solutions
- Before isolating the rack and pinning, try initiating 2-RF’s (reverse filtration) in a row on the rack, then immediately initiate another IT on same rack.
- If bubbles still persist, try rewetting the modules. Rewetting is basically a short (1 hour) CIP ( clean in place ) using only a Caustic/Chlorine solution on the rack in question to “rewet” the fibers. After thoroughly rinsing the rack, initiate another RF, then initiate another IT. (return to module maintenance, rewetting page)
- If bubbles still persist in the clear coupling, isolate the rack, isolate and pin the bubbling fibers.
Mechanical Component Failure
Air Escaping: valve stem packing glands
Air is possibly escaping from around the packing gland on the rack feed header butterfly valves. If bubbles are NOT visible in the clear upper coupling, using an automotive stethoscope or sonic ears, listen to the butterfly valves for “dribbling” accompanied with faint bubbling sounds. We have successfully slowed, if not completely stopped, air from seeping past the butterfly valves and the IT’s are successful.
Air Escaping: Swegelok nuts
Another unexpected source of air escaping is from the swegelok nuts on the air and feed header. To locate this problem requires making a soap solution and spraying both swegelok nuts from the air header to the lower coupling of the modules and observing for bubbles around the fittings. We had quite a few nuts loosen from the vibration caused from the air scrub cycles. While you have your soap solution ready and in use, spray the solution around the module ring nut, we found small amounts of air escaping from the module ring nuts.
Air Escaping: Butterfly Valves
The butterfly valves are not fully seating and isolating the rack from the system. Finding this problem was not an easy one, it required shutting down the WFP, isolating and draining the rack, removing the flanges and dropping out the valve. The valve O rings had become brittle and we had evidence of “wire draw” into the stainless wafer of the valve. We corrected this problem by removing the leaking butterfly valve and replacing the valves with one of the spare valves. A few months later, we experienced the same problem on the same valve. Once again removed the valve from service and replaced the valve with a similar, less expensive, resilient seat valve and the problem has not occurred again for 3 years now. We have replaced 15 original valves with resilient seat valves.
Dual densities within the header and modules
This requires a little more diligence on the operators part in that, we do not see the bubbling from the fibers, but the IT still fails. We used to isolate the rack and pop off the end cap of the influent header to check for mud and or silt accumulation (picture on left) in the line that could cause mixed densities and we would manually flush the header out onto the operating floor. (really made a mess!) We also used to remove the caps on the lower ports of the modules and flush the silt out onto the operating floor. Now we have modified our end caps with valves and banjo fittings that we attach a fire hose to and flush the influent header to the outside, also, we have made a mobile flushing header that attaches to the lower ports on the modules. The flusing header allows us to use the lower side ports to flush out the silt and mud from the modules. This has become part of our regular routine module preventative maintenance program.
For more information about our module maintenance see the article “Preventative Maintenance – header and module flushing”.
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