Why the straight stroke regulating valve stem is smaller

It involves a simple mechanical principle: large sliding friction and small rolling friction. The valve stem of the straight stroke valve moves up and down, and the packing is slightly pressed, it will wrap the valve stem very tightly, resulting in a larger return difference. For this reason, the valve stem is designed to be very small, and the packing is commonly used with a small friction coefficient of tetrafluoroidal packing in order to reduce the return difference, but the problem sent from this is that the valve stem is small, it is easy to bend, and the packing life is short. To solve this problem, the best way is to use the rotary valve stem, that is, the regulating valve of the Angle stroke class, its valve stem is 2 to 3 times thicker than the straight stroke valve stem, and the choice of long life graphite filler, the valve stem stiffness is good, the packing life is long, and the friction torque is small and the return difference is small