Flow through cap for attenuating any noise caused by air flow in a pneumatic servomotor

Claim 1

In a servomotor having a first shell joined to a second shell to form a closed chamber therein, the closed chamber being separated by a wall means to form a front chamber and a rear chamber, the wall means having a hub means with a cylindrical body which extends through an axial opening in the second shell, said cylindrical body having an axial passageway therethrough for communicating the front chamber with the rear chamber and the rear chamber with the atmosphere, said axial passageway retaining a control valve means for regulating the communication of air into the rear chamber in response to movement of a control rod by an operator for developing a pressure differential with vacuum in the front chamber to produce an output force, muffler means for attenuating the noise created as a result of air flowing into said axial passageway from the atmosphere, said muffler means comprising: retainer means connected to said second shell and surrounding said axial opening, said retainer means having a plurality of ribs which engage said second shell to allow air to be presented to the peripheral surface of said cylindrical body; boot means having a sleeve section which surrounds the cylindrical body and a closed end section, said sleeve section having a bead on the end thereof for engaging said retainer means, said closed end section having a lip on the end thereof for engaging the control rod, said boot means establishing a flow path along the peripheral surface of said cylindrical body; cap means having a tubular member with a first shoulder thereon for engaging the cylindrical body and a second shoulder thereon for holding said closed end section of the boot means away from said axial passageway, said tubular member having a plurality of radial openings located between the first shoulder and the second shoulder to establish a fixed cross-sectional area for the flow path to assure that the air present along the peripheral surface can be freely communicated to said axial passageway; and acoustical barrier means located between said second shoulder and said closed end section of the boot means for absorbing noise caused by air inflowing to the control valve means by way of said radial openings in the cap means and the axial passageway.