Pump piston assembly with acoustic dampening device

Abstract

A pump piston assembly has a pump cylinder, at least one hollow piston slidably mounted for reciprocating motion in the pump cylinder, the piston having an inner surface of a first diameter and an outer surface of a second diameter, and a liner sleeve of a different material from the piston mounted on the inner or outer surface of the piston with a close or friction fit to the diameter of the piston surface on which it is mounted. The liner sleeve is of an acoustic dampening material which has a lower acoustic frequency than the piston material and is configured to absorb harmonic acoustic vibrations resulting from reciprocation of the piston in the cylinder.

1 . A piston assembly, comprising:
 a cylinder of a first material;   at least one piston of a second material different from the first material slidably mounted for reciprocating motion in the cylinder, the piston being hollow and having an inner surface of a first diameter and an outer cylindrical surface of a second diameter;   at least one liner sleeve mounted on one of said inner and outer surfaces of the piston and having a close tolerance fit to the diameter of the piston surface on which it is mounted, whereby the opposing surfaces of the liner sleeve and piston are in face to face engagement; and   the liner sleeve being of an acoustic dampening material which has a lower acoustic frequency than the piston material.   
     
     
         2 . The piston assembly of  claim 1 , wherein the liner sleeve is mounted on the inner surface of the piston. 
     
     
         3 . The piston assembly of  claim 2 , wherein the liner sleeve has a central longitudinal axis and opposite axial ends, and the sleeve has a slot extending between the axial ends configured to allow compression of the sleeve during installation into the piston. 
     
     
         4 . The piston assembly of  claim 3 , wherein the slot extends at an angle to the central longitudinal axis of the sleeve. 
     
     
         5 . The piston assembly of  claim 1 , wherein the liner sleeve is mounted on the outer surface of the piston between the piston and cylinder. 
     
     
         6 . The piston assembly of  claim 1 , wherein the liner sleeve is a straight cylindrical tube. 
     
     
         7 . The piston assembly of  claim 1 , wherein the surface of the liner sleeve facing the piston surface has a first mating formation and the opposing surface of the piston has a second mating formation configured for alignment and engagement with the first mating formation when the sleeve is installed. 
     
     
         8 . The piston assembly of  claim 7 , wherein one of said mating formations comprises an annular rib and the other mating formation comprises an annular groove. 
     
     
         9 . The piston assembly of  claim 1 , wherein the acoustic dampening material is plastic or rubber. 
     
     
         10 . The piston assembly of  claim 9 , wherein the acoustic dampening material of the sleeve is an acrylic plastic material. 
     
     
         11 . The piston assembly of  claim 1 , wherein the cylinder is of glass material and the piston is of graphite material. 
     
     
         12 . A gas pump assembly for a medical ventilator, comprising:
 at least a first gas piston assembly comprising a cylinder having a longitudinal axis and a first hollow piston slidably mounted for reciprocating movement in the cylinder and having a piston rod extending out of one end of the cylinder;   a drive unit drivably linked to the piston rod and configured for driving the piston back and forth in the cylinder;   the piston being hollow and having an inner surface of a first diameter and an outer cylindrical surface of a second diameter; and   at least one liner sleeve mounted on one of said inner and outer surfaces of the piston and having a close tolerance fit to the diameter of the piston surface on which it is mounted, the liner sleeve being of an acoustic dampening material which has a lower acoustic frequency than the piston material.   
     
     
         13 . The assembly of  claim 12 , further comprising a second piston assembly identical to the first piston assembly and having a second cylinder with a longitudinal axis extending parallel to the longitudinal axis of the cylinder of the first piston assembly, a second hollow piston slidably mounted for reciprocating movement in the second cylinder and having a second piston rod extending out of the one end of the second cylinder, a second linkage connecting the drive output of the drive motor to the second piston rod, and a second liner sleeve identical to said one liner sleeve and mounted on one of the inner and outer surfaces of the second piston. 
     
     
         14 . The assembly of  claim 12 , further comprising a plurality of additional piston assemblies identical to said first piston assembly, each additional piston assembly having a piston rod drivably linked to said drive motor and a respective hollow piston slidably mounted in the cylinder of said additional piston assembly, and each hollow piston having a liner sleeve of acoustic dampening material mounted on one of the inner and outer surfaces of the respective hollow piston.