A valve apparatus comprising: a valve body defining a chamber and a gland ; a stem extending into the chamber of the valve body, the stem having a valve stem surface ; a shaft disposed in the gland of the valve body such that a seal is formed between the shaft and the gland, the shaft having an end that extends into the chamber of the valve body adjacent the stem; and a cam coupled to the end of the shaft and defining an outer surface to engage the valve stem surface, the outer surface having: a first portion configured to engage the end of the stem in a closed position, a second portion defining a first linear profile configured to engage the end of the stem in an open position, a third portion adjacent the first portion and defining a curved profile configured to engage the end of the stem when the cam is rotated to a first intermediate position between the closed position and the open position, and characterized in that : the outer surface further has a fourth portion between the second portion and the third portion and defining a second linear profile configured to engage the valve stem surface as the cam rotates from the open position to the first intermediate position, and whereby an edge is defined between the first linear profile and the second linear profile and an angle is formed at the edge therebetween. a valve body defining a chamber and a gland ; a stem extending into the chamber of the valve body, the stem having a valve stem surface ; a shaft disposed in the gland of the valve body such that a seal is formed between the shaft and the gland, the shaft having an end that extends into the chamber of the valve body adjacent the stem; and a cam coupled to the end of the shaft and defining an outer surface to engage the valve stem surface, the outer surface having: a first portion configured to engage the end of the stem in a closed position, a second portion defining a first linear profile configured to engage the end of the stem in an open position, a third portion adjacent the first portion and defining a curved profile configured to engage the end of the stem when the cam is rotated to a first intermediate position between the closed position and the open position, and characterized in that : the outer surface further has a fourth portion between the second portion and the third portion and defining a second linear profile configured to engage the valve stem surface as the cam rotates from the open position to the first intermediate position, and whereby an edge is defined between the first linear profile and the second linear profile and an angle is formed at the edge therebetween. a first portion configured to engage the end of the stem in a closed position, a second portion defining a first linear profile configured to engage the end of the stem in an open position, a third portion adjacent the first portion and defining a curved profile configured to engage the end of the stem when the cam is rotated to a first intermediate position between the closed position and the open position, and characterized in that : the outer surface further has a fourth portion between the second portion and the third portion and defining a second linear profile configured to engage the valve stem surface as the cam rotates from the open position to the first intermediate position, and whereby an edge is defined between the first linear profile and the second linear profile and an angle is formed at the edge therebetween. the outer surface further has a fourth portion between the second portion and the third portion and defining a second linear profile configured to engage the valve stem surface as the cam rotates from the open position to the first intermediate position, and whereby an edge is defined between the first linear profile and the second linear profile and an angle is formed at the edge therebetween. <EOS>