Pinning Fibers

Testing for broken fibers, the Integrity Test or IT.

The Integrity Test (IT) procedure drains an entire rack of modules of water and then pressurizes the casing of the modules on the outside of the hollow fibers with air to 30 psi . The fibers must hold air pressure for 5 minutes without a pressure decay of more than .289 psi. When a rack shows signs of air decay, we check the clear coupling at the top of the modules for visible signs of bubbles from the module.  This test is done daily to ensure that none of the hollow fibers have broken.  If an air molecule can get through the wall of a fiber, so can other contaminants in the water get into the fitlered water.

Pinning Fibers

When the Integrity Test results in a module displaying air bubbles rising from the fibers…….., locating, isolating and plugging the broken fiber(s) is accomplished by the process called “pinning”.

A module has 6,350 individual hollow fibers bundled together inside a 6″ PVC housing. The raw water enters the lower end of a module through 1/2″  molded ports in a solid epoxy plug that encases and seals the lower end of all 6,350 individual fibers.  The water floods the entire module around the outside of the hollow fibers.  The water is forced through the micro pourus skin of the fibers and into the hollow center of the tiny hollow tubes, this is where the filtration action occurs.  Water passes through, contaminants are stopped and trapped on the skin of the fibers.  At the upper end of the module there is another epoxy plug, but this time only the tiny, open ends of the hollow fibers have an opening and the 1/2″ molded ports are sealed off.  From these thousands of hollow fibers, clean, filtered water flows out of the module and into the finished water collection header.

This picture is the upper end of the module with the top cap removed.  The bubbles indicate broken fibers and are allowing air to enter those fibers.  These “bubbling” fibers we must “plug” or “pin” which isolates and inactivates the broken fiber because it is no longer an effective tool for filtering out contaminates.

When the module displays bubbles in the upper, clear coupling, we drain the rack and open the leaking module. We carefully bring up the air pressure to the rack and we now observe the open module and watch for where the bubbles are coming from. As the bubbles begin forming, we use our finger to locate the proximity of the leaking fiber. Finding the general area of the leaking fiber(s) we then use a stainless steel pin to locate the exact fiber that is producing the bubbles. As we gently press the tip of the pin into the end of the fiber we can finally find the leaking fiber. Pressing the pin into the fiber end we then gently tap the pin down into leaking fiber and that fiber becomes isolated from the bundle of fibers and becomes a dead end. Other fibers may still be bubbling, continue the isolation process until all leaking fibers have been pinned. Cut off the excess portion of pin that is sticking up to ensure that the top cap does not touch the pins. Assemble the module and bring the rack back on line.

You may see bubbles occur from the modules as you fill the rack and bring it on line, this is normal because the racks have been drained of water during the “Pinning” process, and you are forcing the air from the fibers as water floods into the membrane. We have found that running an RF after filling the rack really helps in purging out the rest of the air from when we pinned the module.

 

 

Do you have any questions, comments, suggestions, experiences you want to share? howieb@ci.st-helens.or.us