Dentist chair repair


Old 09-09-11, 09:38 AM
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Dentist chair repair

I am repairing a dentist chair that has been flooded. The tech didn't dry out the chairs electronics and hydraulics before turning the power on so the chair has issues. Here is what I am seeing:

1) Power to PC board is on
2) Relays LEDs light up when pedal is pressed
3) when I place the jumper on the board to factory settings it moves the chair
4) in normal operation the chair doesn't lift or lower everything else seems to work
5) the pump housing is extreemy hot

I am going to replace the pump system with another from same style of chair. If the chair is lowered and the back is lowered the lines will not be under pressure right? I am diong it this way so I can then remove the supply lines, pump and cap to test the other chair before ordering new parts. Does anyone have any suggestions as to what is wrong or any problems with how I am going about this? My main concern is that I don't injure myself during removal of hydraulic lines and how to contain the oil while disassembling.

Any help would be appreciated!!

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Old 09-09-11, 11:37 AM
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Not sure we got you in the right sub-forum, but as long as you can find the thread should be okay.

Yes, if the hydraulics are compressed (collapsed) should be no pressure. There wouldn't be a lot of pressure anyway with only the weight of the chair compressing the hydraulic cylinders, but it might make it more messy when you crack the lines open; instead of a dribble you'd get a bit of a stream. I confess I've never worked on a dentist's chair, but hydraulic systems are a pretty generic kind of beast; the switches, pumps,valves, and actuators all work in more or less the same way depending on the application.

Couple of thoughts:

1. Hydraulic pumps get hot. Whether yours is abnormally hot is a matter of degrees (no pun intended).
2. Working on hydraulic systems is a messy business; generally no way around that. Drip pans, lots of rags, speedy dry.

My gut instinct is that something is fried on the control board or in the electrical control system, i.e. a fried solenoid valve based on the fact you can make it work hydraulicly. Also given a flood situation, the water would generally have little effect on a hydraulic system as far as the fluid portion of the system, i.e. pump, cylinders, lines, unless the water got into the hydraulic fluid. Energizing a wet/damp electrical/electronic system is more more likely to have caused problems in that portion of the system.
Old 06-01-12, 08:56 PM
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optical exam chairs

I too am trying to troubleshoot an electro hydraulic chair.
1.) It raises all the way up, but as it comes down it vibrates and makes a humming noise.
2.) The electronic panel only works when it is raised all the way up.
3.) I have the equipment, but have never refilled a hydraulic system.

I am looking for some troubleshooting advice and a manual on maintaining electro hydraulic chairs. If any one can help me I would be very grateful. I am also willing to pay for the manual.
Old 06-02-12, 05:53 AM
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Welcome to the forums! I'd wait until more seasoned hydraulic people chime in, but the vibration you are experiencing on descending is likely air in the fluid. You may not have fluid at full capacity,
Old 06-02-12, 07:10 AM
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The "down" side might be simply gravity, i.e. to raise the chair hydraulic pressure is applied to the cylinder but to lower it the valve is simply opened and the weight of the chair pushes the fluid back out into the reservoir. In addition to air in the system that chandler suggests, it might also be a simple stick & slip situation of the hydraulic cylinder piston rod [the chrome piece that goes in and out] and the piston rod seal. Pretty easy to eliminate that as a possibility by applying a bit of lubrication to the rod when it's extended. Pretty much any lubricant will do, but don't over do as it will attract dirt.
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