Discover the magic of the holder valve. Proper air pressure and the many functions of your delivery system rely on accurate pressure to operate u2014 we talked about this in previous Practice Tips. This issueu00a0discusses the differences between "normally open" vs "normally closed" holder valves.
Automatic Delivery Systems
Most delivery systems are u201cautomaticu201d systems. Being automatic means that whichever handpiece you pick up is the one that runs when you step on the foot control. Control the activation of the handpiece by a valve in the handpiece holder. The valve in the holder allows air to flow through and into the handpiece block to control activation. These valves will have two hoses attached to them u2013 one for air flowing in, the other for air to flow out (and to the handpiece block). There are two different configurations of valves in these systems: u201cnormally openu201d and u201cnormally closed.u201d
Normally Closed Systems
In a normally closed system, the valve closes when you remove the handpiece from the holder. This stops the flow of air to the block, whichu00a0pushesu00a0down on a diaphragm to prevent the handpiece from running.
This type of system was employed by A-dec for many years andu00a0implemented in other brands of current systems. A-dec moved to a relief valve system that only has one hose attached to it. Some common brands that use this type of valve are A-dec (prior to c. 1992), Beaverstate, Belmont, DCI, Engle, Forest, Marus, and Pelton & Crane. The normally closed valve is more commonly used than the normally open valve. See below for a diagram of this system.
Normally Open Systems
In a normally open system, the valve opens when you remove the handpiece from the holder. Thisu00a0allows air to flow through the valve. In these systems, the air flows into the block and pushes up on the diaphragm to allow the handpiece to run. The only brand weu2019re familiar with that uses normally open valves is Dental-Ez, but there are certainly others. See below for a diagram of this system.
NOTE:u00a0In both types of systems, the handpiece runs when it is removed from the holder.u00a0A unit that doesnu2019t allow the handpiece to run when removed from the holder wouldnu2019t make much sense, would it?
The magic of the holder valve helps to determine between a normally open or closed holder valve. It' s important to locate where air flows through the valve.Is it when you hang the handpiece up or is it when you lift the handpiece up? p>
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