controlled by hydraulic means the latter consists of plunger 9 positioned through actuator stem 22 into cavity 11 which is filled with a suitable hydraulic fluid such as oil any additional penetration of plunger 9 into cavity 11 will displace hydraulic fluid which in turn causes a downward move of piston 12 or 12a after overcoming the resistance of the spring 20 this then effectively narrows the gap 17 16 and increases fluid resistance on the other hand retraction of plunger 9 will cause a corresponding increase in gap width and therefor a decrease in fluid resistance the typical maximum width of the gap between surfaces 16 and 17 is 0 015 34 this combined with a typical radial distance of fluid travel of 0 250 34 makes the fluid mechanically important l d ratio at least 34 1 which will keep most fluid conditions in the laminar regime which in turn will vary the fluid resistance or amount of fluid being passed under constant pressure drop to the third power of the gap width 34 h 34 as discussed previously this assures an outstandingly wide range between maximum and minimum controlled flow which far exceeds the capabilities of conventional throttling valves for example a typical embodiment of my invention can vary the amount of gas flow from less than 1 cc min at 100 psi pressure drop to more than 10 000 cc min as shown in a graph of test measurements depicted in fig2 in contrast conventional needle type valves heretofore used seldom exceed a flow range of 50 1 an added benefit from the hydraulic positioning means employed in my invention.