referring now to fig1 numeral 2 indicates a generally vertically extending oil well production line , which may be a well casing or a separate pipe therein , the apparatus of the present invention , indicated generally by numeral 4 , being depicted mounted therein . referring now to fig2 there can be seen the apparatus of the present invention , indicated generally by the numeral 4 , in isolation ( i . e . not mounted within the production line ), wherein the present invention comprises , from top to bottom , an upper valve housing 6 and a lower valve housing 8 , connected together by internal , lower collar 10 having an annular valve seat 11 ; an upper collar 12 having a larger upper bore 14 and a lower , annular valve seat 16 , is mated with the machine - threads provided in the top end of the upper valve housing 6 ; an upper shaft 18 , or upper axle 18 , mounted on its lower end to a lower , solid head member 20 having a substantially conical top portion 21 , and mated on its upper end to an upper , solid head member 22 , such as by set screw 24 ( head member 22 hereinafter referred to as upper valve member 22 ); a substantially conical , solid head member 26 having a lower threaded stud 28 which is mated into a machine - threaded central bore 30 provided in upper valve member 22 for receiving same ; a pair of generally semi - circular vanes 32 pivotally mounted on upper valve member 22 by means of a pivot pin 34 , which extends through upper valve member 22 and through upwardly extending ears 36 on the vanes 32 . upper valve member 22 is provided with a pair of diametrically spaced bores 38 terminating at their lower ends in smaller openings 40 through which shanks 42 of slidable thrust plugs 44 slidably extend . the shanks 42 are positioned to bear at their lower ends on the upper surfaces of their respective vanes 32 , each at a position laterally displaced from the pivot pin 34 . within each bore 38 is a compression spring 46 , bearing at its lower end on the thrust plug 44 , held under compression by an adjustable threaded plug 48 threaded into the upper end of the bore 38 . thus , plugs 48 may be preset or pre - adjusted to provide the desired valve of compression force stored in springs 46 and thus predetermine the torque applied by shanks 42 to the vanes 32 , which torque normally holds vanes 32 in the tilted or oblique position shown in fig1 and 2 . in the preferred embodiment of the present invention , adjustable threaded plug 48 is preset or pre - adjusted to provide a compression force to springs 46 which makes vanes 32 non - responsive to any amount of upward fluid pressure , the degree of the tilt of the vanes 32 being solely adjustable by means of vane adjustment nut 52 which is provided with internal threads to mate with the machine - threaded portion 54 of upper axle 18 below upper valve member 22 . the degree of the tilt of the vanes 32 regulates the amount of fluid allowed to flow therepast . the machine - threaded portion 54 of upper axle 18 is calibrated to indicate the amount of fluid which would be allowed to flow past the vanes 32 at the particular setting selected . in the preferred embodiment , the machine - threaded portion 54 of upper axle 18 is calibrated with two separate sets of markings for indicating the flow which would be permitted past vanes 32 , for the various settings of the vane adjustment nut 52 , one set of markings representing the calibration for natural gas flow and the other set of markings representing calibration for crude oil flow . as is further apparent from fig4 the downwardly facing area of each vane 32 is considerably greater on one side of the pivot pin 34 than the area of that vane on the other side of pivot pin 34 . thus , any upward fluid pressure applied to the lower surfaces of the vanes 32 will apply a net torque thereto in direction tending to rotate each vane about the pivot pin 34 in opposition to the torque provided by the compression springs 46 . referring again to fig2 a lower , reciprocable shaft 56 , or lower axle 56 , is provided with machine - threads at its top end for mating a machine - threaded , lower , central bore 94 provided through lower valve member 20 . lower shaft 56 extends through and is journalled in o - ring seals 57 , 58 and bushings 60 , 61 within seal housing 63 whereby it is rotatable therein and axially movable therethrough . seal housing 63 is affixed within lower valve housing 8 by means of fins 85 or spiders 85 being welded , for example , to the inner wall of lower valve housing 8 and the outer surface of seal housing 63 . a compression spring 72 surrounds the lower shaft 56 from a point substantially downstream from bushing 61 , in the preferred embodiment , downwardly to a point substantially near the lower end of lower shaft 56 . compression spring 72 is retained onto shaft 56 by means of washer 65 , and one or more spring retainer nuts 66 , 67 . plug - in 74 is inserted into the bottom end of seal housing 63 , thereby fluidly sealing seal housing 63 , thereby preventing fluid flow therethrough except through breather vents 75 , 76 which permit the intake and exhaust of fluid . in operation , the upper valve housing 6 and the lower valve housing 8 are inserted into the oil well production line 2 , the larger upper bore 14 of upper collar 12 being threaded for mating an adaptor ( not shown ) which engages a down hole lock ( not shown ) within the bore of production line 2 , thereby securing upper valve housing 6 and lower housing 8 within the bore of production line 2 . o - rings 88 , 90 ensure a fluid seal between the upper and lower valve housings 6 , 8 and the oil well production line 2 . when production fluid is flowing upwardly into conduit 2 , that flow of fluid past the tilted vanes 32 will apply an upward fluid pressure to the lower surfaces of the vanes , thereby applying a net torque thereto in a direction tending to rotate each vane about the pivot pin 34 in opposition to the torque provided by the compression springs 46 thereby ensuring that vanes 32 remain in their preselected tilted position and only a certain amount of fluid passes between the vanes and the inner walls of upper valve housing 6 . it will also be obvious that the rotation of tilted vanes 32 will cause the upper axle 18 and the upper valve member 22 and lower valve member 20 mounted thereto , and lower shaft 56 , to also rotate . the vane adjustment nut 52 is manually , or otherwise , adjusted to the desired setting to allow a preselected amount of fluid flow past the vanes 32 and through the upper valve housing 6 and therethrough through the production line 2 . some of the fluid flowing through the production line 2 upwardly into the lower valve housing 8 will enter through breather vents 75 , 76 of plug - in 74 to prevent buoyancy of plug - in 74 , which would cause an undue increased velocity of fluid flow , thereby resulting in malfunctioning of the device . any increase in fluid flow beyond the amount of fluid flow desired to be allowed past vanes 32 as is predetermined by preselecting the setting of vane adjustment nut 52 , will cause an increased rotation of vanes , 32 , thereby creating a rotating / lifting force on vanes 32 , thereby causing the upper axle 18 , upper valve member 22 , the lower valve member 20 , and the lower shaft 56 , to simultaneously rotate and be lifted and ultimately head member 26 of upper valve member 22 will engage its seating surface 16 , and top portion 21 of lower valve member 20 will engage its seating surface 11 , thereby stopping all flow of fluid through lower valve housing 8 and upper valve housing 6 . the above described lifting / rotating action is enhanced by the action of compression spring 72 ; in its normal state , spring 72 tends to hold the valve open , it is decompressed as best shown in fig1 with its lower end bearing on bushing 60 and its upper end pushing against bushing 61 therefore , any lifting of the upper valve member 22 and the lower valve member 20 causes a commensurate compression of compression spring 72 , thereby upwardly urging lower shaft 56 , lower valve member 20 , upper axle 18 , and upper valve member 22 . thusly , compression spring 72 enhances the rotating / lifting action caused by an increased velocity of fluid flow past vanes 32 , thereby substantially lessening the time gap between the point at which the velocity of fluid flow exceeds the maximum allowable flow according to the setting of the vane adjustment nut 52 , and the seating of the head member 26 of upper valve member 22 with its valve seat 16 and the seating of top portion 21 of lower valve member 20 with its valve seat 11 , thereby preventing a potentially damgerous situation in the event that the production line 2 may rupture or break , or in the event of a sudden surge of high pressure in the production line it is important to note that breather vents 75 , 76 serve as pressure equilization means to permitting a flow of oil or gas into the interior of chamber 63 , which houses spring 72 , since chamber 63 is sealed against the flow operating valve head members 20 , 22 and vanes 32 . the provision of two valve members and the provision of a spring - action lower shaft are major improvements over the prior art , as they facilitate a more effective , and quicker action sealing means to prevent the flow of fluid through the valve , thereby preventing potentially dangerous situations , either subsurface or at the surface . note that when the fluid flow is decreased below the preselected maximum level , the lowermost movement of lower valve member 20 is defined by the upper surface of seal housing 63 . while specific embodiment of the present invention has been shown and described , the same is merely illustrative of the principles involved and other forms will be obvious to those skilled in the art , within the scope of the appended claims .