of the valve body and terminates in a generally conical end wall 22 within the valve body a fluid passage 24 extends coaxially with the bore 20 from the conical end wall 22 to communicate with the outlet bore 16 an internally threaded counterbore 26 is formed in the bonnet 20 for mounting a valve guide member 30 the elongated guide valve member 30 has an axial bore or barrel portion 32 formed therein and external threads thereon for engaging the internal threads of counterbore 26 a radial shoulder 34 on the outer surface of the valve guide provides a positive stop limiting movement into the bonnet the shoulder 34 prevents damage to the seat 54 from excessive torque on the valve guide 30 a resilient o ring 36 mounted in a chamber 38 provides a fluid tight seal between the bonnet 20 and the external surface of the valve guide a valve stem 40 having a generally cylindrical portion acting as a piston is slidably mounted within the cylindrical barrel 32 of the valve guide for movement between a fully open position shown in fig1 and a fully closed position shown in fig2 one or more o ring grooves 42 are formed in the cylindrical piston portion of the valve stem for receiving an o ring seal 44 to provide a fluid tight seal between the valve stem and the valve guide a radially inwardly extending flange 46.