Can anyone tell me that if your pressures are good on your deair and flow pump do you still need to check the motor brushes for problems? I have a 2008K here thats giving me a cycling high flow error and a stable conductivity of 12.6 My deair and flow pressures are fine, I swapped the cfs and acfs and that didn't work. I swapped a couple of valves that I thought it could be and the same problem. Someone told me that it might be the bc membranes but id rather not mess with it uless I know thats whats wrong for sure. I've wasted enough hours mis- diagnosing the problem anyway.

Hi Robb,

The brushes are the electrical contact points inside the motors that provide the current for the motor to run. It's all or nothing with the brushes. Either they are supplying electricity or they are not. So, if the motor is running at proper pressure, the brushes are working correctly. If you notice the motor quitting when it shouldn't, even for a second, then I would go to the brushes. Sometimes when they wear way down the contact will break sporadically and cause intermittant flow problems.

Thanks Fred That helps alot. I'll check to make sure that they are running ok. Do you have any suggestions as to what the High flow error is due to?

Sorry Robb, but it sounds like a tear in the BC membranes.

Besides a membrane tear, it could also be the float switch, cfs transducer or a stuck valve.

this works for me all the time... when I test the bc for tears ..I lower the flow to 300... n take the drain line off the back of the machine. let the machine run for 2 minutes. the flow should completly stop every cycle. if you see water dripping, then u have a tear membrane/s. good luck

I had already swapped the float switch and cfs's. The only thing left for me was the bc. I took it apart and sure enough it was the membranes. Thanks to you all for the input.

Why don't you perform the Maual Balancing Chamber Valve Leak Test that is in the Troubleshooting guide. This works great and saves alot of time that you have allready wasted. This test only takes a few min. and it is very reliable too.

My BAD... try the Testing for a Leaking Balancing Chamber Diaphragm. Again this test is right on the money!

Is that test described in the trouble shooting guide? I'm fairly new to machine repair and go about trouble shooting the only way I know how and so far that has been using this website and trial and error.

The flow motor does run at variable speeds/voltage depending on the DFR selected. Unlike the dear. motor which runs at a single speed. I would recommend diassembling and cleaning the dust out of the flow motor reassemble and recal. Then move on to BC membranes if the problem persists.

My advice , based on over 20 years of experience is that when you start getting intermittant low and high flow errors, it is almost 100% of the time, a sticky intermittantvalve on the balance chamber. Good luck trying to find it using diagnostics, if you are very lucky you might get it. I just replace the entire balance chaber complete....eliminates it completely for years ...also , assures trouble free dialysis for the patient, which comes first of course... How many times has the machine been pulled off a patient during treatment for this error...not worth it.

Dear Robb.
Remember: 1- Fresenius machine can´t measure the flow, the machine just can calculate the flow based on the balancing chamber switching time. Ex: If the select flow is 500ml/min.
Desired flow = 500
Balancing chamber internal value = 30ml (theorical value)
One minute = 60 seconds
500/30 = 16,66 times (16,66 = number of balancing chamber in one minute)
60/16,66 = 3,6 seconds (3,6 time to switch to balancing chamber A to B e vice versa).
To make the counts more simple, i consider the measure time as one minute, machine uses a small time to take measure, so the machine can calculate the flow not in one minute but at each second and show the equivalent flow in ml/min.
2- to check if the 24V DC motor is ok, you need to measure the resistence on the motor terminal, if the resistence is < 1,9 ohm the motor is ok, if the resistence is > 2,0 ohm, you need to check the motor brushes and rotor contacts (when i said motor ok, i belive the bearings and move parts are ok too).
3- Solenoid valves with intenal seal broken cause a oxid inside the solenoid were the parts move, this make or cause a diference in the open/closed (on/off) time due to the rust inside of the magnetic circuit of the valve causing a flow flutuations. You can check the balancing chamber solenoid valve, removing one by one and open the valve (disassembly) to see if there isn´t rust, corrosion, broken seal ´o`ring, or change all the 8 balancing chamber (expensive way).
You need to check if there are glock orifice or valve, if the volume of solution entered in balancing chamber is lower, the time will be reduced and the flow will varie (change or intermitent).
Robb, 95% of chance of balancing chamber valve fail.
Hope you understand, and sorry my poor inglish.
Carlos.