Methods and apparatus of determining an integrity risk of a satellite reference system are provided. The bladed pulley having spaced apart blades and an open, central volume configuration to permit conveyed material to fall through the pulley. A computing section computes a dot population density in corresponding one of a plurality of sub data areas. In one presently preferred embodiment, a hydraulic actuator which may be a fail-safe actuator, is connected to a gate valve utilizing an operating stem which extends through a first bonnet secured to one side of a gate valve body.