Saturday, 21 September 2013

Hydrim L110W CF14 Flow Switch Error

I have a Hydrim instrument washer (Hydrim L110W from SciCan) which has been experiencing a CF14 flow switch error. For those of you unfamiliar with this equipment, it is a professional washer that uses a special liquid soap and heated water to cleanse operatory equipment. It is essentially a "super dishwasher".

The washer pumps special liquid detergent at certain times of the wash cycle into the machine. There are some sensors that check whether or not this process is successful, just in case you run out of soap or if there is a fault in the pump (which is a peristaltic type). The main sensor involved with the "CF14 flow switch error" is a flow switch made by Gentech, model FCS-X008A. Some examples can be found on this Gentech Sensors page.

The most disappointing part of all this is the machine is relatively new, only 4 years old. For the cost of this machine, I would have expected at least a 5 year warranty, but it only comes with a 1 year. This is a disgrace for the industry, in my opinion. In any case, SciCan itself will not directly sell end-users parts and everything in Canada must be done through a few oligopolistic dental supply companies. Fortunately, suppliers in the USA or other countries will be happy to provide servicing information and parts. A great deal of information can be found in this Service Manual as well as on this SciCan Parts Document (pages 98-112).

To complicate matters, a flow switch error may also indicate the actual flow is weak due to the pump or tubing. Use of a peristaltic pump means wear and tear on the tubing inside the pump, which may need to be replaced periodically. The above Parts Document PDF shows a preventative maintenance kit which comes with most of the parts that need periodic replacement. However, sometimes the flow switch is simply "stuck" and when the microprocessor is listening to the sensor during the dose pumping period, it may get a faulty reading. The way the sensor works is when there is no flow, it reads infinite resistance (open switch). When fluid flows, it slides a small plastic segment containing a magnet to another position, resulting in the switch closing (resistance becomes close to zero).

So why does a 4 year old flow switch stick already? Turns out there is a small rubber stopper covering over the end of the magnet inside the plastic segment. The flow switch is mounted vertically, with fluid flowing up against gravity. When there is no flow, the inner plastic segment with magnet and rubber stopper is resting in the down position (gravity pulls it down over an opening). The rubber gets "sticky" as it deteriorates, perhaps accelerated due to the detergent. It causes the switch to stick in the down position. Normally when the pump starts, the flow should raise the plastic segment with the magnet up against gravity, "closing" the switch (resistance becomes zero) which notifies the microprocessor that flow is indeed occurring. If this does not happen, a CF14 error occurs.

I think this is a design flaw, especially for this application. The use of a rubber stopper over the magnet to "seal" against back-flow in the flow switch is not needed. The peristaltic pump itself should provide enough resistance to resist back-flow. At least a better, more-resistant material should have been used to cover the magnet that would not deteriorate and crumble over time. I also believe this flow switch is not designed to be used with detergent, only clean water. I will find out shortly as I have contacted Gentech to see if this is the appropriate sensor for this application. In my experience with other equipment, both electronic and mechanical, it is often these "little things" which are over-looked that cause most failures.

For example, take a look at this Brother Printer Unable 32 error, which happened to my Brother 4040CDN printer. The linked document shows how a bit of foam material over a shutter used to cover a sensor can cause it to stick after a few years, messing up a sensor that is used to read toner density and distribution. That piece of foam sticking, which costs a fraction of a cent, will completely shut down your printer. Unless you "dive in" to try to fix it yourself (assuming you find the problem and solution), you would probably spend tons of money trying to fix it. Searching Brother's website for this error provides nothing useful. In fact, the above document is the ONLY one I ever found that actually gets to the heart of the problem and which fixes it, and it was NOT created by Brother (who would prefer to have you throw out your printer and buy a new one). Unfortunately it requires dismantling most of the back end of your printer, just to put a bit of tape over the foam so it is not as sticky. But this is a perfect example of how a silly "less than a penny" material can completely bring an expensive piece of equipment to it's knees (like the tiny rubber stopper on the Hydrim flow switch).

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