If you have a broken toggle on your dental unit, knowing the basics of toggles help you with a quick and easy repair. Toggles, or more accurately, toggle valves, activate a wide variety of items on a typical pneumatic dental unit. On all toggle valves, the physical plastic switch that you flip typically depresses a valve stem (“plunger”) within the valve body to allow or prevent the passage of air or water.
As shown above, the valve body uses a pin to hold the toggle together. Normally there are 4 holes (at 90° positions) through which the pin can pass. This allows the toggle to rotate in 90° increments., so it can flip up, down, left or right to activate.
Types of Toggle Valves
All toggle valves perform this same basic function – why then are there so many different names for them? These terms are qualifiers for how the air or water goes through and/or what happens after the valve closes (turns off).
- Momentary Toggles
- On/Off Toggles
- Relieving Toggles
- Non-Relieving Toggles
Momentary Toggles
A momentary valve only remains in one position (normally on), as long as you hold the toggle. The toggle springs back into the other (“off”) position as soon as it releases. Use momentary toggles for short-term applications, such as unit purges or cuspidor cup fillers – things that do not run for a prolonged period.
On/Off Toggles
The opposite of momentary is just on/off. The toggle flips in one direction to turn it “on” and flips again in the opposite direction to turn it “off.” Use these for things you want in a specific position for a prolonged period. This would include a master on/off switch for the entire delivery unit.
Relieving Toggles
Use a relieving toggle to activate a secondary valve. Air will always pass through a relieving toggle to activate the secondary valve. When the toggle turns “off” it relieves and allows the air in the line to escape through the toggle to turn off a secondary valve. A brief hiss will be heard.
Example: Think of a garden hose with a sprayer attachment on the end. Even if you turn the garden hose off at your house, you still have water pressure in the hose. That pressure remains until you relieve it by squeezing the trigger on the sprayer.
As it happens, one of the most common applications for a relieving toggle is for water on/off control. The toggle is used to send air pressure that pushes on a water valve that then turns your water on. Until that pressure relieves, the water runs. So, while only air passes through the toggle, it’s quite common for a relieving toggle to be used for water activation.
Non-Relieving Toggles
The opposite of relieving toggle is the self-explanatory non-relieving toggle. A non-relieving toggle normally feeds directly to an outlet from which air or water expels in some way. For example, the spout of a cup filler on a cuspidor.
NOTE: These two properties of a toggle valve are not mutually exclusive. A toggle valve could be both momentary and relieving. Such a valve would only stay in one position as long as it is held there. Then it springs back to the other position when released. This valve would also have air flowing through it, and relieves, when the toggle turns off. Pneumatic arm locks often have a momentary relieving toggle used with them. Pneumatic arms are often held in place with air pressure. This pressure relieves when the toggle is momentarily held in the off position, but restores as soon as the toggle releases and springs back into the on position.
Barb Configuration
Additionally, toggles come in various barb configurations. In other words, the barb fittings (see our previous issue on fittings for more information) will be on different locations of the toggle. The standard configuration is to have one port on the back (side opposite the toggle) and one on the side. Normally, the back is the inlet and the side is the outlet. However, the two ports can be in other places, both on one side, both on the back, one on each side, etc. The only reason to have the barbs in an unusual location is because there is no room within the unit for the barbs elsewhere.
For example, on some older A-dec cuspidors, the cup filler toggle is placed on the inside of a narrow metal casing, so the toggle is surrounded on 3 sides by the metal of the unit case. This only allows room for the barbs to stick out of the toggle at the bottom:
Nonetheless, this toggle functions identically to any other standard on/off toggle. Water passes in one barb, and when the toggle flips, the water passes out the other barb (and pours out of the cup filler spout). If this toggle were placed elsewhere (with more space around the toggle), any other barb configuration would work just as well.
When replacing a toggle valve, always make certain you know what is actually flowing through the valve (air or water). Know what you have room for in your unit (where the barbs can be), and if you want the toggle to stay in one position after flipping it or not. Hopefully this Practice Tip on the delivery unit toggle basics help you choose the right one for your needs.
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