Practice Tips #19: Toggle Basics

Toggles, or more accurately, toggle valves, are used to 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 toggle is held into the valve body using a pin. Normally there are 4 holes (at 90° positions) through which the pin can pass. This allows the toggle to be rotated in 90° increments so it can flip up, down, left or right to activate – whatever you need or desire.

All toggle valves perform this same basic function– why then are there so many different names for them: relieving, momentary, etc? These terms are qualifiers for how the air or water is allowed through and/or what happens after the valve is closed (turned “off”).

Momentary Toggles

A momentary valve will only remain in one position (normally “on”) as long as the toggle is held. The toggle will spring back into the other (“off”) position as soon as it is released. Momentary toggles are often used for short-term applications, such as unit purges or cuspidor cup fillers – things which you would not normally need to have running for a prolonged period.

On/Off Toggles

The opposite of momentary is just on/off. The toggle is flipped in one direction to turn it “on”, and then flipped again in the opposite direction to turn it “off”. Such valves are used for things that you will want in one position or the other for a prolonged period (such as the master on/off switch for the entire unit).

Relieving Toggles

A relieving toggle is used to activate a secondary valve. Air will always pass through a relieving toggle to activate the secondary valve. When the toggle is turned “off” it will relieve allowing the air in the line to escape through the toggle (a brief hiss will be heard) so that the secondary valve can shut off. Think of a garden hose with a sprayer at the end. Even if you turn the garden hose off at your house, you still have water pressure in the hose. That pressure will remain 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 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 is relieved, the water will run. So, while only air will actually pass 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 will normally feed directly to an outlet from which air or water is expelled in some way (e.g. the spout of a cup filler on a cuspidor).

Note: These two properties of a toggle valve are not mutually exclusive, that is, 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, and would then spring back to the other position when released. This valve would also have air flowing through it, and this air would relieve, when the toggle is in the off position. Pneumatic arm locks will often have a momentary relieving toggle used with them. Pneumatic arms are often held in place with air pressure. This pressure is relieved when the toggle is momentarily held in the off position, but is restored as soon as the toggle is released 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 not 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 is flipped, 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), 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.


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