Variable area flow meter

Abstract

A variable area flow meter for measuring the volumetric flow of a fluid flowing through the flow meter includes a body portion having a fluid inlet, a fluid outlet portion and a channel. A fixed boundary is defined between the channel and the fluid outlet portion. A fluid flow path extends between the fluid inlet and fluid outlet. A piston is arranged within the channel and longitudinally displaceable by the flow of fluid. The cross-sectional area of a portion the fluid flow path is variably determined by the structural shape of the piston and the instantaneous location of the piston relative to the fixed boundary. The longitudinal displacement of the piston in the direction of the fluid flow and consequently the cross-sectional area of the portion of the fluid flow path are dependent on the volumetric flow rate of the fluid.

1 . A variable area flow meter for measuring the volumetric flow of a fluid flowing through the flow meter comprising: 
 a body portion having a fluid inlet a fluid outlet portion and a channel and defining a fixed boundary between the channel and the fluid outlet portion;    a fluid flow path extending between the fluid inlet and fluid outlet;    a piston arranged within the channel and longitudinally displaceable by the flow of fluid;    wherein    the cross-sectional area of a portion the fluid flow path is variably determined by the structural shape of the piston and the instantaneous location of the piston relative to the fixed boundary whereby the longitudinal displacement of the piston in the direction of the fluid flow and consequently the cross-sectional area of the portion of the fluid flow path are dependent on the volumetric flow rate of the fluid.    
   
   
       2 . The variable area flow meter according to  claim 1  wherein the cross-sectional area of the portion of the fluid flow path increases as the displacement of the piston increases in the direction of the flow of fluid.  
   
   
       3 . The variable area flow meter according to  claim 1  wherein at least one longitudinally extending recess is formed in an outer surface of the piston and the said portion of the fluid path is defined by the fixed boundary and the at least one tapered recess.  
   
   
       4 . The variable area flow meter according to  claim 3  wherein the at least one recess extends longitudinally in a V-shape such that the width of the at least one recess decreases in the direction of the flow of fluid.  
   
   
       5 . The variable area flow meter according to  claim 3  wherein the depth of the at least one recess varies in the direction of the flow of fluid.  
   
   
       6 . The variable area flow meter according to  claim 5  wherein the depth of the at least one recess increases in the direction of the flow of fluid.  
   
   
       7 . The variable area flow meter according to  claim 5  wherein the depth of the at least one recess decreases in the direction of the flow of fluid.  
   
   
       8 . The variable area flow meter according to  claim 3  wherein a lower portion of the at least one recess is flat.  
   
   
       9 . The variable area flow meter according to  claim 3  wherein a lower portion of the at least one recess is curved.  
   
   
       10 . The variable area flow meter according to  claim 1  wherein the piston is a hollow cylinder with a closed leading end and at least one aperture is formed in the cylinder wall, wherein the said portion of the of the fluid path is defined by the fixed boundary, the at least one aperture and the hollow cylinder.  
   
   
       11 . The variable area flow meter according to  claim 10  wherein the at least one aperture is V-shaped and extends longitudinally along the cylinder wall such that the width of the at least one aperture decreases in the direction of the flow of the fluid.  
   
   
       12 . The variable area flow meter according to  claim 10  wherein the at least one aperture is V-shaped and extends longitudinally along the cylinder wall such that the width of the at least one aperture increases in the direction of the flow of the fluid.  
   
   
       13 . The variable area flow meter according to  claim 10  wherein the at least one aperture is rectangular in shape and extends longitudinally along the cylinder wall.  
   
   
       14 . The variable area flow meter according to  claim 1  wherein the channel further comprises a pressure relief region arranged directly above the portion the fluid flow path and adjacent the fixed boundary of the channel.  
   
   
       15 . The variable area flow meter according to  claim 1  wherein the cross-sectional width of the piston varies in the direction of the flow of fluid.  
   
   
       16 . The variable area flow meter according to  claim 1  further comprising cleaning means for cleaning the variable area flow meter.  
   
   
       17 . The variable area flow meter according to  claim 16  wherein the cleaning means comprise a cleaning membrane arranged to move longitudinally within the channel so as to clean an internal surface of the channel.  
   
   
       18 . The variable area flow meter according to  claim 16  wherein the cleaning means comprise a cleaning membrane arranged to clean the piston as the piston is longitudinally displaced.  
   
   
       19 . The variable area flow meter according to  claim 1  further comprising biasing means operative to urge the piston in a direction opposite to the displacement of the piston resulting from the fluid flow.  
   
   
       20 . The variable area flow meter according to  claim 19  wherein the biasing means comprise at least one member selected from the group comprising a spring, repelling poles of a magnet and gravity.  
   
   
       21 . The variable area flow meter according to  claim 1  further comprising indicator means for indicating the volumetric flow rate of a fluid in response to the longitudinal displacement of the piston along the channel in the direction of the flow of fluid.