Patent GB-833453-A (GB)
Title: Improvements in or relating to free piston seals
IPC: F04B47/12
Filed: 1956-06-27
Abstract: 833,453. Pistons; packing. PAN AMERICAN PETROLEUM CORPORATION, [formerly STANOLIND OIL & GAS CO.]. June 27, 1956 [Jan. 26, 1956], No. 19872/56. Class 122 (1). [Also in Group XXVIII] A variable-diameter metallic sealing element for a free piston suitable for use in a tube-well having diametrical tolerances comprises a number (n) of ring segments 27 with alternate segments oppositely disposed on each side of a ring 45 mounted on the piston body 12, the ends of each segment transverse to the longitudinal axis 51, Fig. 3, having surfaces a b<1> h<1> g and c d i j contained by planes which intersect at an angle alpha on a line 55 intersecting the longitudinal axis of the piston in the plane of the mean diameter of the seal, the segments having outer peripheral surfaces of a radius R equal to half the mean diameter of the seal and internal surfaces 44, 44<1>, Fig. 1, having a mean radius r equal to the external radius of the ring 45; the angle # which the internal surfaces make with the axis of the segment and to a coaxial cylindrical surface g o j, Fig. 3, is equal 11 of segments are provided on this piston and in each case the upper segments 27 are hingejointed, at their ends 26 remote from the overlapping portions, to a member 24 which is axially slidable on the tubular body 12 of the piston and the lower group is similarly hinged to a member 43, also slidable on the piston body 12 and urged towards member 24 by a spring 42 having an abutment 41 secured by set-screws to the body 12. The inner faces 44, 44<1> of the overlapping portions of the segments 27 bear on the ring 45, which may be fixed or, as shown, slidable on the piston body 12. As the distance between the members 24, 43 increases or decreases the seal formed by the overlapping portions of the segments 27 contracts or expands as the effective diameter is varied in accordance with the position of the inclined inner faces of the segments on the ring 45, which when free is self-centring between the opposed groups of segments. A seal 46 prevents leakage between the ring 45 and the outer face of the piston. Movement of the upper group of segments 10 is effected by the attachment of the slidable member 24 by pins 19, 23 to a control rod 17 passing through the body and having attached to its lower end, Fig. 2, an axially movable cylindrical chamber 37 within which is a plunger 14 fixed by a rod 16 to the bottom of the piston body. The chamber 37 is supported in the body by a spring 38, the initial tension of which may be adjusted by calibration washers 39. In operation, the free piston is dropped into the well with the sealing elements contracted by the action of the spring 38. It falls until a point is reached when the external fluid pressure causes the top of the chamber 37 to move axially towards the plungger 14, thereby compressing a gas which has been supplied to the chamber at a predetermined pressure. Continued pressure on the exposed end of the control rod 17 causes further downward movement of the member 24 and thus expands the sealing elements until. they bear on the tube walls. The seals may be locked in their expanded positions by a snapaction device comprising a pair of spring- loaded rollers 35, Fig. 1, which ride over fixed toggle-blocks 36 during the downward movement of the control rod until the rollers pass the lower edge of the blocks. As the piston returns to the well head, under the influence of the pressure on its lower face, variations in internal diameter of the tube are accommodated by the action of the springs 42 which tend to expand the groups of seals continuously. As the liquid above the piston is discharged, the pressure in chamber 37 causes upward movement of the member 24 until the snap-action device operates to secure the sealing segments in their contracted position and the piston again falls to the bottom of the well, the sealing elements being thereby cleansed of solid matter, such as paraffin wax, which may have accumulated during the upward movement.