fig1 a , 1 b are elevation and sectional views of my pump 10 in its collapsed state . an inner cylinder 11 is nested within an outer cylinder 12 . the top end of the outer cylinder 12 is necked down to a diameter matching the outside diameter of the inner cylinder 11 . the bottom end of the inner cylinder 11 is flared outward to a diameter matching the inside diameter of the outer cylinder 12 . the flaring and necking are over a relatively short dimension , for example 20 mm , and at a relatively small angle , for example 2 degrees . these cylinders and their conical portions may be produced by secondary forming of extruded tubes , or by injection molding , or by other known methods . the bottom end of the outer cylinder 12 includes a fluid inlet check valve 13 . the inlet valve 13 includes passages 14 for water intake into the pump intake chamber 15 . the passages 14 also act as coarse filters to prevent large debris from entering the pump . the inlet valve 13 includes a top planar valve seat 19 . the annular bottom edge of the outer cylinder 12 abuts the valve seat 19 . an inlet valve flap 18 is a flexible membrane of elastomeric material such as viton or neoprene . the inlet valve 13 is a check valve . in operation , piston upstroke draws water into the pump inlet chamber 15 ( below the piston ) with the valve flap 18 flexed upward . at the end of the upstroke , the valve flap 18 lies back over the valve seat 19 to hold that water in the inlet chamber 15 . a nozzle housing 30 on the top of the inner cylinder 11 includes a bearing through which a pump shaft 20 is movable up and down , and a discharge port 17 to expel water in a generally horizontal direction . shaft 20 is of a rust - proof material such as stainless steel , brass , or plastic . the shaft 20 includes a handle 21 on its upper end . its lower end is shouldered and threaded . a lift check valve 22 includes an axial bore to fit onto the shaft 20 and is secured to the lower end of the shaft by a nut 23 . the lift check valve 22 includes a lower body with water passages 24 through it . the lower body is shouldered to a diameter slightly smaller than the inside diameter of the inner cylinder 11 allowing it to slide loosely within the inner cylinder 11 . the shoulder of the lower body forms a seat for a lift check valve membrane 26 . the lift check valve membrane 26 is a thin flexible membrane with a circular perimeter and an axial hole . the membrane 26 is mounted on the valve housing 22 by stretching it over a flange in the axial portion of the diaphragm valve housing . the lift check valve 22 is constrained in this location between the housing shoulder and flange . the diaphragm valve membrane is typically 0 . 5 mm thick , and its diameter is slightly less than the inside diameter of the inner cylinder 11 . the pump shaft 20 , lift check valve 22 , valve membrane 26 , and nut 23 together form the piston subassembly . a flotation collar 35 of a durable foam material fits snugly over the outer cylinder 12 and extends along its length . the flotation collar 35 is thick enough to float the entire pump . as an example , the flotation collar of fig1 is about 2 . 5 ″ diameter and volume about 14 . 9 cubic inches . fig2 shows the pump in the extended position . detail a shows the necking of the outer cylinder 12 mating with the flare of the inner cylinder 11 to form a water tight seal . interference between the two conical sections creates a wedge lock . the desired angle of the mating conic sections produces a lock sufficient to resist normal pumping forces , though not sufficient to resist a sharp axial shock or a twisting push . if the angle is too large , the inner and outer cylinders may not lock . if the angle is too small , one or both cylinders could fracture from stress , or lock too tightly . because the pumping operation requires two hands , one to hold the pump and one to operate the piston , the holding hand can resist the downward force of pumping action and minimize the tendency of the cylinders to unlock . fig3 shows the extended pump with the piston moving upward . upward motion of the piston creates a slight vacuum pressure under the piston , causing the diaphragm valve to seal against the seat area of the diaphragm valve housing , and the inlet valve 2 to flex off its seat on the inlet valve housing . if the lower end of the pump is immersed in water , water will flow into the chamber intake below the piston , and water above the piston will be expelled through the nozzle 17 . fig4 shows the piston in downward motion . positive pressure is now created in the chamber below the piston , closing the inlet valve against its seat and stopping flow in the lower end of the pump . the positive pressure below the piston opens the lift check valve 22 upward , allowing water to flow into the upper pump chamber . this action transfers water from the lower inlet chamber to the upper discharge chamber for discharge ( on the following upstroke ) through the nozzle 17 . while the preferred embodiment utilizes interference of flared and necked sections of the inner and outer cylinders respectively to limit extension , and to lock the cylinders in position , other arrangements might instead be employed . one example is shown in fig5 in which extension limitation and locking are accomplished with threaded sections of inner and outer cylinders . another arrangement might include tabs on the inner cylinder and slots in the outer cylinder to limit extension and lock the cylinders in the extended position . in the following claims , any terms indicative of orientation ( e . g . upper , lower ; top , bottom ; horizontal , vertical ) are meant only to correspond with the illustrations and to facilitate an understanding of the claimed invention . such terms are not intended as positive limitations . the foregoing description , including any dimensions , of a preferred embodiment is illustrative . the concept and scope of the invention are not limited by such details but only by the following claims .