Dental Unit Foot Control
The foot control of your dental unit is a critical component in the proper operation of your operatory. While we are all aware that this round silver disk allows us to control the speed of the handpiece it is less commonly known the part it plays in proper handpiece water control. The foot control is supplied with a main ¼ inch air line that is regulated just below 80 pounds per square inch of pressure. This means that even though the pressure in the compressor tank can vary as much as 20 psi, up and down, there is always a regulated non-changing amount being supplied to the foot control. This regulated air supply is used in three ways by the foot control. First of all there is a main valve that opens in response to the pressure of the foot on top of the disk. As the disk is pressed harder the air supplied to the handpiece increases from 0 psi to a preset maximum of about 40 psi. This air is sent from the main valve back to the unit in a second ¼ inch air hose. When the pressure of the foot is removed from the disk the main valve shuts down and opens up quickly releasing the pressure that is going to the handpiece. If the main valve is sluggish the handpiece may continue to run for a few seconds before releasing the air. A properly working main valve will quickly make a “psst” of air when released and the handpiece should begin to stop immediately. The second and third ways that the regulated air is used involve the chip air and the water pilot air. Attached to the main valve in the foot control is another valve called the pilot air valve. The pilot air valve is designed so that even a small push on the disk will send a full pressure air supply back to the unit in a 1/8 inch hose to be used for the chip air on the handpiece. When the foot control is released the chip air from the pilot valve turns off and the pressure dissipates out the chip air hole at the front of the handpiece. The pilot air valve also supplies a full pressure air supply to a small toggle valve on the top of the foot control. This toggle valve is used to turn the water supply on and off to the handpiece. When the toggle valve is turned on the full pressure air is allowed to go back to the unit in another 1/8 inch air line where it pushes open another valve that is hooked up to water thus turning on the water to the handpiece. When the foot control is released the pilot valve quickly shuts down and releases the air pressure in this air line. It is important that the air be released quickly so as to minimize the amount of water that drips from your handpiece. If the pilot air valve is sticking at all, the water will continue to drip from your handpiece unit the pilot air valve resets and releases the pressure.
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The most common problems with the foot control involve air leaks and the sticking of the main valve or the pilot air valve. Your foot control should not leak air at all if you are not pushing it or if you are pushing it and holding it. You should only hear an air release for a brief second or two after pushing and releasing the disk. Test this by picking up the foot control and holding it to your ear. Now squeeze and hold the disk down with your hand. Little or no air should be heard to escape. Finally release the foot control and you should immediately hear the psst of releasing pressure. If the psst is delayed by a few seconds your control should be serviced. Finally any continuous leak from the foot control can be very hard on your clinic’s compressor. We have seen compressors fail due to a foot control leak.