My project at last night’s SGVTech meet was to dig into a nonfunctional cordless water flosser, the Waterpik WF-03. I added this to my evening tooth brushing & flossing routine upon recommendation of my dental hygienist, and it worked for several months before it stopped running. At first I thought it just needed new batteries, but when I opened the watertight battery compartment, out poured brown water along with the three AA batteries. Clearly something has failed inside the device.
There were no obvious ways to disassemble this device, which I’m sure is partially motivated by a desire to control water intrusion. Given the high potential for disassembly to be a destructive process, it’s not realistic to expect I could repair the device and return it to service. But somewhere inside is a battery-powered water pump designed to deliver short high pressure pulses, and I am confident I can find a fun use for such a device in the future.
The first thing I tried was prying off the silvery front panel. I had hoped maybe it was held by clasps, but it was clearly glued in place. I had also hoped there would be fasteners visible below this panel, but no luck. The only visible part is the switch controlling high/low/off operation.
Prying at various places of the plastic enclosure by hand, the only parts that moved at all were near the bottom, flanking either side of water resorvoir. I started prying by hand and, when that wasn’t enough, moved on to a screwdriver.
Looking at the seams I broke apart with the screwdriver, the plastic components are either glued or welded together. There’s definitely no turning back in this disassembly. Once the screwdriver pried a few pieces of plastic open, I could enlist the use of pliers to continue pulling plastic apart.
Once I could see enough into the interior to have a good idea where a cutting blade could do some good, a hack saw was enlisted to finish the job.
Once the front outer shell is cut all the way around the base, the mechanical guts slides out easily.
There’s a smaller piece of enclosure on the back, designed for the water reservoir to slide and clip into. Removing this required removing the water intake pipe O-ring (visible in lower left of picture) and removing two screws.
Once the back was removed, we are free to disassemble the central cylinder. It bottom was secured to the battery tray via four screws, and its top was held to the water intake and valve assembly with four more screws.
Here’s another view of the disassembled parts, laid out roughly analogous to the way they were when assembled.
Once we could see the motor gearbox assembly inside that cylinder, it was clear why this device stopped working: water has leaked past the diaphragm (black) and made its way to components below that point.
If there were any lubrication on the gears, they have been washed away. And the motor’s external casing has corroded. It was not possible to move this mechanical assembly by hand, so we took it apart to see what has seized.
When the motor was removed, it looked even worse than expected. Trying to turn its output shaft using fingers found it unwilling to move.
But we were able to un-seize the shaft, possibly helped by an unintentional drop to the ground. Then after cleaning it up a bit and adding some oil to the bushings, it spins up again! Markings on this little motor proclaims itself to be genuine Mabuchi. Whether it is indeed the real thing or a knockoff manufacturer brazenly using the name I can’t tell, but any motor that can survive abuse, end up looking like this one, and still spin up again has my respect.
We reassembled the water pump core and it was pumping water again.
We could pump water past the point where a Waterpik nozzle would mate with a rubber O-ring, but it started leaking out past that point as those sections weren’t designed to control water flow. I didn’t expect the pump to be so tightly integrated with the nozzle socket assembly and didn’t bring one of my spare Waterpik nozzles. But that was no barrier: we fashioned a substitute using a short length of pneumatic hose and parts from a ball point pen.
I wouldn’t use this for my dental home care anymore, but it’s certainly going to sit in my pile of interesting parts awaiting integration into a future project. [Update: No future project. After it damaged other items with more rusty water, I threw them all away.]