A valve, comprising: a body; a flow passageway defined within the body; a flow-control seal positioned within the flow passageway; a piston extending through the flow passageway and the flow-control seal, the piston defining a first direction and a second direction of an axis; a fluid supply conduit in fluid communication with a first portion of the flow passageway extending from the flow-control seal in the second direction, the fluid supply conduit configured to provide a fluid flow applied at the perimeter of the piston in the first portion of the flow passageway; a fluid outlet conduit in fluid communication with a second portion of the flow passageway; a force means configured to apply a force on the piston in the first direction along the axis; wherein the flow-control seal contacts the body and the piston and thereby separates the first portion and the second portion of the flow passageway to substantially prevent fluid communication between the first portion and the second portion of the flow passageway when the piston is in a first position wherein the flow-control groove is displaced from the flow-control seal in the first direction; wherein, when the piston is displaced in the second direction, opposite to the first direction to a second position, the flow-control groove extends at least partially beyond the flow-control seal in both the first direction and the second direction, whereby the fluid supply conduit is in fluid communication with the fluid outlet conduit through the first portion and the second portion of the flow passageway; and characterized in that the valve further comprises: a flow-control groove defined in the piston, wherein the flow-control groove defines a depth extending into the piston, and wherein the flow-control groove does not extend around the entire circumference of the piston, wherein the depth of the flow-control groove gradually increases in the first direction from a proximal end to a distal end to be configured to gradually increase the flow of fluid between the first portion and the second portion of the flow passageway as the piston is displaced in the second direction. a body; a flow passageway defined within the body; a flow-control seal positioned within the flow passageway; a piston extending through the flow passageway and the flow-control seal, the piston defining a first direction and a second direction of an axis; a fluid supply conduit in fluid communication with a first portion of the flow passageway extending from the flow-control seal in the second direction, the fluid supply conduit configured to provide a fluid flow applied at the perimeter of the piston in the first portion of the flow passageway; a fluid outlet conduit in fluid communication with a second portion of the flow passageway; a force means configured to apply a force on the piston in the first direction along the axis; wherein the flow-control seal contacts the body and the piston and thereby separates the first portion and the second portion of the flow passageway to substantially prevent fluid communication between the first portion and the second portion of the flow passageway when the piston is in a first position wherein the flow-control groove is displaced from the flow-control seal in the first direction; wherein, when the piston is displaced in the second direction, opposite to the first direction to a second position, the flow-control groove extends at least partially beyond the flow-control seal in both the first direction and the second direction, whereby the fluid supply conduit is in fluid communication with the fluid outlet conduit through the first portion and the second portion of the flow passageway; and characterized in that the valve further comprises: a flow-control groove defined in the piston, wherein the flow-control groove defines a depth extending into the piston, and wherein the flow-control groove does not extend around the entire circumference of the piston, wherein the depth of the flow-control groove gradually increases in the first direction from a proximal end to a distal end to be configured to gradually increase the flow of fluid between the first portion and the second portion of the flow passageway as the piston is displaced in the second direction.