in one embodiment of the invention which is shown in fig1 a substantially conical mandrel 1 is located within a complementary cylinder 2 , a substantial portion of the inside surface of which is conically shaped with a cone angle equal to that of the mandrel 1 . mandrel 1 is mounted concentrically within the cylinder 2 so that the clearance space between the mandrel and the cylinder is substantially equal to the radial thickness of the rings to be expanded . the internal surface of cylinder 2 is cylindrically shaped at the rear to provide a breach 6 which accommodates a mechanism for applying the rings to the small diameter end of the mandrel . the mandrel 1 has an extended portion 4 at the small diameter end which is substantially cylindrical rather than conical to facilitate loading the mandrel . a loading port 5 is provided through the wall of cylinder 2 through which rings to be expanded pass with the plane of the ring being at right angles to the mandrel axis . when each ring has entered breach 6 a shuttle loader 7 moves forward from the position shown in the diagram and pushes a ring ( 3 ) forward and over the extended portion 4 of mandrel 1 . the forward face of shuttle 7 is provided with a bore 8 having a diameter slightly greater than portion 4 of the mandrel so that the ring contact surface 9 of shuttle 7 is able to move forward over the surface of the mandrel to ensure that the loaded ring 3 is left at a position forward of a cylinder port 10 . shuttle 7 then executes a rearward stroke to return to the position shown in the diagram . the force required to move ring 3 to the large diameter end of the mandrel 1 is provided by a fluid ( for example , air ) under pressure . this is introduced through port 10 and during the supply of this fluid the loading port 5 is sealed so that the pressure in the breach 11 at the rear of the ring is increased substantially over the pressure forward of the ring producing a differential force which moves the ring forward along the mandrel surface . the pressure of the applied fluid is suitably adjusted to ensure that each ring to be expanded is moved the full length of mandrel 1 . mandrel 1 is mounted within cylinder 2 so that a small amount of axial movement is possible and is forwardly biassed by the use of a compression spring so that a rim 11 formed in the large diameter end of mandrel 1 abuts against an inwardly directed flange provided at the end of cylinder 2 . accordingly when a ring reaches the large diameter end of mandrel 11 it is prevented from moving off the end of the mandrel by making contact with flange 12 . when it is desired to release the expanded ring a ring applicator tool or object to be sealed or clamped is presented at the mouth 13 of cylinder 2 and pushed against the end face 14 of mandrel 1 to move the mandrel rearwardly against the spring force to provide a gap between rim 11 and flange 13 through which the expanded ring moves under its own elastic forces . the edges of rim 11 are suitably curved to facilitate release of the ring from the end of the mandrel . known control equipment is used to supply a charge of pressurised fluid through port 10 in sequence with the reciprocating motion of shuttle 7 and subsequent depression of mandrel 1 . the rings to be expanded are contained in a hopper and fed through loading port 5 under the influence of gravity . a fresh ring drops into the breach 6 each time shuttle 7 moves rearwardly clear of the exit way of loading port 5 . in a second embodiment of the invention illustrated in fig2 and 4 the rings to be expanded are moved along the mandrel mechanically . the mandrel 20 is supported on the upper edge of a reciprocating push rod 21 and loosely restrained by a housing or cage comprising two transversely spaced parallel rods 22 and hoops 23 . the mandrel is free to float in the longitudinal direction and in particular may be slid rearward of the position in which it is shown in fig3 and 4 . push rod 21 slides on a rail 24 fixed to the expander body 25 and its primary purpose is to engage a ring to be expanded and force it over the mandrel 20 . the push rod is moved longitudinally by a pneumatic ram 26 via a right angle link plate 27 . the leading face of the push rod is shaped to form a nose 28 which when the push rod is moved forward from its rearward or loading position impales a ring supported in the bottom of chute 29 by a loading member 30 . loader 30 is free to slide up and down in chute 29 and the purpose of this movement will be explained later . the loader is channel shaped in cross section and together with the front wall of chute 29 defines a guide whereby rings from a hopper 31 are delivered to the loading position . the side walls at the bottom of loader 30 are curved inwards at 32 ( see fig2 ) to support the lower most ring ( shown dotted ) at a position such that the axis of the ring is in line with the centre line of the push rod nose 28 . a slot 33 is provided in the bottom of the rear wall of loader 30 to allow the push rod to continue in forward direction without interference after snaring the bottom ring . rubber rings are stored in a hopper 31 and pass into chute 29 oriented in a vertical plane . the chute is always full with the bottom ring held by loader 30 as already explained . in order to ensure rings enter chute 29 from the hopper the rings in the hopper must be agitated from time to time . this is accomplished by the provision of fingers 34 and 35 which project vertically through the hopper floor 36 and are reciprocated by an arm 37 driven by cam 38 . cam 38 is in turn rotated counterclockwise to move arm 37 upwards via a roller assembly 39 fixed to push rod 21 . each time push rod 21 nears the end of a forward stroke fingers 34 and 35 are moved upwards to be later returned to their original position by virtue of a weight 40 when the push rod executes its return stroke and disengages the roller assembly from the cam . in addition to the agitating action of fingers 34 and 35 loader 30 is also reciprocated in synchronism . that is , the top of loader 30 is projected up into the interior of hopper 31 from the mouth of chute 29 . it is for this purpose that a loader slidable within chute 29 is required . arm 37 is fixed to loader 30 to cause this movement . operation commences with the pneumatic ram 26 extended and push rod 21 at the rear extremity of its stroke so that nose 28 is rearward of loader 30 . the lowermost ring in chute 29 is held in the loading position by loader 30 . under the control of a pneumatic control system of a known configuration the ram is retracted and push rod 21 moves forward . push rod nose 28 snares the ring presented by loader 30 and carries it forward so that it is impaled by the tip 41 of mandrel 20 . the push rod continues its forward motion dragging the ring along the mandrel expanding it as it does so . because of the forces exerted by the ring on the mandrel the mandrel is moved forward within hoops 23 until it abuts against an end plate 42 . near the end of the expansion stroke roller assembly 39 engages cam 38 and the rings in the hopper are agitated by fingers 34 , 35 and loader 30 . at the end of the stroke ( as shown in fig3 ) the ring is prevented from sliding off the mandrel by end plate 42 . this plate is provided with an apperture in registration with and of approximately equal diameter to the large end of the mandrel . the expanded ring is transferred from the mandrel to an applicator tool or directly to the article about which it is to be placed by pushing the tool or article against the recessed face 43 of the mandrel . the mandrel moves back ( as it is free to do within the limits of the cage within which it floats ) and the ring rolls off the mandrel to contract about the tool or article . the rim 44 on the large end of the mandrel is curved to facilitate release of the ring . the operation of the return stroke apart from allowing the cycle to be repeated causes fingers 34 , 35 and loader 30 to return to their normal position . loader 30 thereby locates the next ring in the loading position . in moving the ring to the large diameter end of the mandrel it will be appreciated that considerable frictional forces must be overcome as well as the elastic restoring forces in the ring . to reduce the frictional force the mandrel is preferably made from a material having a low coefficient of friction , for example , ptfe or stainless steel . alternatively a surface coating having a low coefficient of friction could be applied to a body material having a higher coefficient of friction .