Needleless injector with shock absorbing means between ram and piston

Abstract

A needleless injector has a syringe body having an opening at one end, a piston housed within the syringe body for urging a liquid within the syringe body through the opening and a ram for driving the piston. A shock absorbing component is provided for reducing an initial transfer of force from the ram to the piston. The initial rate of pressure increase on the liquid is reduced, thereby controlling the rate of collapse of gas bubbles in the liquid.

1 . A needleless injector comprising: 
 a syringe body having an opening at one end;    a piston housed within the syringe body for urging a liquid within the syringe body through the opening;    a ram for driving the piston;    means for applying a force to the ram; and    means for reducing an initial transfer of force from the ram to the piston.    
     
     
         2 . The injector of  claim 1 , wherein the force-reducing means comprising a component associated with the ram and/or the piston.  
     
     
         3 . The injector of  claim 2 , wherein the force-reducing means comprises a cylinder, in which an end of the ram is slidably received.  
     
     
         4 . The injector of  claim 3 , wherein the cylinder forms part of the piston.  
     
     
         5 . The injector of  claim 3 , wherein the cylinder is closed at one end, the closed end lying adjacent the piston, and wherein the ram is received adjacent the open end of the cylinder before the application of force to the ram.  
     
     
         6 . The injector of  claim 3 , wherein the cylinder is open at both ends.  
     
     
         7 . The injector of  claim 6 , wherein the internal opening of the cylinder has a constant internal diameter.  
     
     
         8 . The injector of  claim 6 , wherein the internal opening of the cylinder has at least two internal diameters, a first internal diameter at an end of the cylinder for cooperation with the ram, and a second smaller internal diameter.  
     
     
         9 . The injector of  claim 8 , wherein the internal opening of the cylinder has three internal diameters, a third internal diameter at an end of the cylinder for cooperation with the piston, the third internal diameter being greater than the second internal diameter.  
     
     
         10 . The injector of  claim 9 , wherein the third internal diameter is equal to or greater than the diameter of the ram.  
     
     
         11 . The injector of claims  3 , wherein the cylinder has a length of between 1 mm and 5 mm.  
     
     
         12 . The injector of claims  3 , wherein the ram is slidably received in the cylinder with a fluid tight fit.  
     
     
         13 . The injector of  claim 1 , wherein the force-reducing means comprises a compressible member.  
     
     
         14 . The injector of  claim 1 , wherein the means for applying a force to the ram comprises a source of pressurized gas.  
     
     
         15 . A method of delivering liquid from a needleless injector syringe which comprises a piston housed within a syringe body and a ram for driving the piston thereby causing liquid to be driven out of the syringe, the method comprising: 
 applying an initial force to the ram to initiate delivery of the liquid;    during a first stage of the delivery reducing the initial force applied to the ram and applying the reduced force to the piston; and    during a second stage of the delivery, transferring a substantial portion of the initial force applied to the ram to the piston.    
     
     
         16 . The method of  claim 15 , wherein the initial force applied to the ram is reduced in the first stage by spacing the ram from the piston, the spacing being reduced during the first stage.  
     
     
         17 . The method of  claim 16 , wherein when the spacing is reduced during the first stage, the movement of the ram towards the piston causes compression of a closed volume of gas.  
     
     
         18 . A needleless injector comprising: 
 a syringe body having an opening at one end;    a piston housed within the syringe body for urging a liquid within the syringe body through the opening;    a ram for driving the piston;    means for applying a force to the ram; and    means for controlling the speed of bubble collapse within the liquid.    
     
     
         19 . The injector of  claim 18 , wherein the pressure in the syringe body increases to a pressure of about 1 to about 5 Mpa upon applying a force to the ram.  
     
     
         20 . The injector of  claim 18 , wherein the size of a bubble present within the liquid collapses to about {fraction (1/20)} or less of an original size.  
     
     
         21 . The method of  claim 15 , wherein, during the first stage of the delivery, the pressure within the syringe body increases to a pressure of about 1 to about 5 Mpa.  
     
     
         22 . The method of  claim 21 , wherein the increase in pressure occurs within 200 μs.