an effective axial expansion of the piston fore chamber 22 with the result being a partial vacuum in the piston fore chamber 22 there is no practical resistance to the movement of the piston 16 as the tube 92 is in fluid communication with the after chamber 24 the piston 16 is then driven toward the closed valve 68 driving of the piston 16 compresses the fluid in the piston fore chamber 22 thereby forming a compressed fluid having a greater pressure and temperature than the fluid in the annulus 146 typically it is desirable that the pressure of the compressed fluid in the piston fore chamber 22 be at least 30 psi greater than the pressure of the fluid in the annulus 146 the pressure and the temperature of the compressed fluid in the piston fore chamber 22 may be measured by the pressure measuring device 58 temperature measuring device 62 and reported to the computer 120 the valve 68 is then opened releasing the compressed fluid through the second conduit 70 around the right angle bend 86 the expanding compressed fluid moves around the right angle bend 86 through the second segment 88 exiting the opening 90 into the t head connector 80 the t head connector 80 volume is much greater than the regions that the compressed fluid has passed the result of the larger volume is that the compressed fluid rapidly decompresses releasing mechanical energy in the form of a sonic event the sonic event is transmitted through the fluid in the t head connector 80 into the annulus 146 the measurement of the level of liquid in annulus 146 is determined by the doppler effect as received by the microphone 110.