An air-operated double diaphragm pump, the pump comprising: a pair of chambers (43a;43b) defining a volumetric space fillable with air and fluid wherein the volumetric space within each chamber (43a;43b) is separated into an air side and a fluid side by a diaphragm (44a;44b); a shaft movable between a first terminal point and a second terminal point wherein the shaft is fastened to each diaphragm (44a;44b) in the pair of chambers (43a;43b) and wherein the shaft includes a plurality of indentations disposed radially lengthwise along length of the shaft, wherein the indentations allow passage of air; a bushing adapted to receive the shaft, the bushing and shaft being in sliding engagement with each other, the bushing includes at least two vents formed on the bushing and a hole formed at each respective terminal portion of the bushing to allow passage of air; and a slide valve traversable between one position and another position for directing compressed air from a compressed air inlet into a chamber (43a;43b) based on the position of the slide valve; wherein the indentations disposed along the shaft and hole formed at each terminal portion of the bushing are alignable to create a path for air to travel from the compressed air inlet to a compressed air outlet and generate differential pressure to cause the slide valve to change direction and direct air to another chamber (43a/43b) characterized in that: the bushing further includes ribs protruding radially outwards from inner surface of the bushing toward the shaft and disposed along length of the bushing, said ribs varying the inner diameter of the bushing at different sections along the length of the bushing to increase bushing relief area; said pair of chambers (43a;43b) are connected to the compressed air outlet and allow compressed air to bleed freely through the compressed air outlet; and said slide valve changes position before the compressed air in the air side of the chamber (43a;43b) becomes fully vacated and the remaining compressed air in the air side of the chamber (43a;43b) is utilized to pressurize the chamber (43a;43b). a pair of chambers (43a;43b) defining a volumetric space fillable with air and fluid wherein the volumetric space within each chamber (43a;43b) is separated into an air side and a fluid side by a diaphragm (44a;44b); a shaft movable between a first terminal point and a second terminal point wherein the shaft is fastened to each diaphragm (44a;44b) in the pair of chambers (43a;43b) and wherein the shaft includes a plurality of indentations disposed radially lengthwise along length of the shaft, wherein the indentations allow passage of air; a bushing adapted to receive the shaft, the bushing and shaft being in sliding engagement with each other, the bushing includes at least two vents formed on the bushing and a hole formed at each respective terminal portion of the bushing to allow passage of air; and a slide valve traversable between one position and another position for directing compressed air from a compressed air inlet into a chamber (43a;43b) based on the position of the slide valve; wherein the indentations disposed along the shaft and hole formed at each terminal portion of the bushing are alignable to create a path for air to travel from the compressed air inlet to a compressed air outlet and generate differential pressure to cause the slide valve to change direction and direct air to another chamber (43a/43b) the bushing further includes ribs protruding radially outwards from inner surface of the bushing toward the shaft and disposed along length of the bushing, said ribs varying the inner diameter of the bushing at different sections along the length of the bushing to increase bushing relief area; said pair of chambers (43a;43b) are connected to the compressed air outlet and allow compressed air to bleed freely through the compressed air outlet; and said slide valve changes position before the compressed air in the air side of the chamber (43a;43b) becomes fully vacated and the remaining compressed air in the air side of the chamber (43a;43b) is utilized to pressurize the chamber (43a;43b).