In each block, the following processes occur,
(a) The lateral passages for the drive air, air coolant, and signal air
intersect with longitudinal passages that lead to the front surface of the block.
(b) Parallel to these, other longitudinal passages lead to the handpiece
drive air barb, the handpiece pressure gauge, the handpiece air coolant barb, and the
cap for the water valve.
(c) It is here, at the surface of the block, that air from the foot control is
either held back or allowed to flow through and run the handpiece.
(3) The front cover of the control block has three cavities in the inner
surface. These cavities in the cover correspond in location to the three groups of
passages drilled in the front of the block. When the block is assembled, with the
diaphragm in place between the block and the cover, the cavities allow the diaphragm
to deflect away from the surface of the block, so air can flow between the grouped
(4) However, the flow between the grouped passages can occur only if the
diaphragm is allowed to deflect into the cavities in the cover. Air pressure from the
handpiece hanger valve or the handpiece selector valve, applied into the cavities,
presses and holds the diaphragm against the block. This prevents any flow between
the passages, so the handpiece cannot operate.
(5) In automatic control systems, placing a handpiece in its hanger actuates
the hanger valve to supply the "holdback signal" that pressurizes the cavities in the
cover and shuts off the control block. Lifting the handpiece out of its hanger releases
the holdback signal allowing air to pass through the control block. In manual control
systems, the manually-operated selector valve accomplishes this task.
(6) Water coolant for the handpiece is controlled by an integral water valve
in the control block. The water is supplied through a passage from the master block.
This passage intersects with the water coolant flow control needle valve bore. After
passing the needle valve seat, the water flows to the inlet seal at the bottom of the
water valve stem. Unless the water valve is actuated, the flow of water is blocked at
(7) Actuation of the water valve occurs when air pressure is applied above
the water valve diaphragm in the water valve cap. The signal air reaches the water
valve cap after passing the holdback diaphragm at the front of the control block. When
the signal air reaches the water valve cap, it deflects the diaphragm downward. This, in
turn, pushes the stem downward and unseats the inlet seat, allowing water to flow
through the valve to the outlet barb.