Welcome back! In previous Practice Tips #3 (previously known as Tech Tips) we discussed the basics of dental units and the required operating pressure (80 psi air, 40 psi water). After a few technical calls from dentists lately, we thought it would be a good topic to revisit.
As discussed before, insufficient air pressure can lead to a myriad of problems. In most systems, air is also used to prevent handpiece function. Air flows through the handpiece holder (see below for a holder or go to our holders & bars for more variety) pushing down on a diaphragm to keep the handpiece from running when it's in the holder. For this system to work, the main air pressure needs to be higher than your drive air, so that it can keep the drive air from forcing its way through the system. This is another reason your main pressure needs to be quite high (typically 80 psi).
If you have a cuspidor, air pressure can be used to activate the water to rinse the bowl and fill the cup. For systems with a timer (the bowl rinse or cup filler will run for a time and then automatically shut off), an air reservoir is typically used to provide the timing. When activated (usually via a pilot valve- #10-10), air flows into the reservoir which gradually drains as it flows into a block to turn the water on. Once the reservoir is emptied of air, the pressure is released on the water valve and the water then shuts off. The timer adjustment simply controls how long it takes for the air to empty from the reservoir.
Since water is denser than air, air pressure needs to be at least twice your water pressure for the air activated functions to work more efficiently. Otherwise, the greater density of water can allow it to “force” its way through the lines.
Your foot control, also, operates under standard regulated line pressure. The foot control is the first point at which your drive air pressure is stepped down. By having a solid 80 psi inlet pressure, you have plenty of range to control the outlet pressure. If the pressure came in at only 40 psi (for example), you’d have much more difficulty getting a full 40 psi to your handpiece when you need that much power.
Your foot control may also have air operated accessories, such as a water on/off toggle. You need ample air pressure at this toggle for the same reason as you need high air pressure inside the unit. Of course, you can’t have 80 psi in the operatories unless you have enough pressure coming out of your compressor, which should be set to cycle at 90-100 psi (to support the inevitable loss of pressure as it travels). The regulators (#05-54) in the operatories can only step the air pressure down, so you need to be sure the pressure coming into the room is in excess of 80 psi. Adequate air pressure is the first step in keeping your units running well.
We can't tell you how many calls we get that could be quickly diagnosed in-house had the doctor simply checked the gauges first, so don't forget to check yours when experiencing issues with any dental unit component. Please give us a call at 800-331-7993 with any questions.
Thanks for reading and see you next month!
Hello amerdental.com owner, Nice post!
Hi, my dental unit has a problem: when I touch the foot control in order to use the high speed handpiece, it starts to run, than the air pressure rapidly goes down and it almost stops working.The same with the other 2 lowspeed handpieces.The air pressure in air/water spray it’ s normal, the water on cuspidor flows normaly.Any ideas?Thanks.
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