【文章內(nèi)容簡介】 ? 33 1. Rotary Equipment Electric motors The process industry uses electric motors to operate pumps, generators, pressors, fans, blowers and other equipment. Electric motors are either direct current (DC) or alternating current (AC). The operation of an electric motor is based on three principles: ? Electric current creates a magic field。 ? Opposite magic poles attract each other, like magic poles repel each other。 ? Current direction determines the magic poles. ? 34 1. Rotary Equipment Electric motors Electric motor consists of: Stationary mag (stator) Moving conduct (rotor) Permanent magic field is formed by the lines of force between the poles of the mag. When electricity passes through the conductor in a DC motor, it bees an electromag and generates another magic field. ? The twin fields increase in intensity and push against the conductor. 35 1. Rotary Equipment Electric motors The rotor in an AC motor is a slotted iron core. Copper bars are fitted into the slots. Two thick rings hold the bars in place. Alternating current flows into the stator, producing a rotating magic field. The stator artificially creates an electric current in the rotor, which generates the second magic field. When the two fields interact, the rotor turns. ? 36 2. Stationary Equipment Piping and storage tanks Gate globe, and ball valves Filters Heat exchangers Cooling towers furnaces Boilers Reactors Distillation columns ? 37 2. Stationary Equipment 38 Chapter 2. Valves Valve─ a device to direct and control the fluids by starting, stopping, and throttling (restricting) flow to make processing possible. Valves─are designed to withstand pressure, temperature, and flow and can be found in homes and industry across the world. 39 Chapter 2. Valves The mon valves found in the manufacturing environment are: Gate valve Ball valve Check valve Butterfly valve Plug valve Needle valve Threeway valve Diagragm valve Relief valve Safety valve Angle valve Multiport valve ? globe valve 40 Chapter 2. Valves Process operators classify valves by: Classification of valve Flowcontrol element function Operating condition ? Gate valve ? Globe valve ? Needle valve ? Check valve ? Plug valve ? Adjusting valve ? Cutoff valve ? Threeway valve ? Handoperating valve ? Safety valve ? Electricoperated valve ? Pneumaticoperated valve Connecting manner ? Flange connection ? Threaded connection ? Clamp connection ? Welding connection ? 41 Chapter 2. Valves A device that places a movable metal gate in the path of a process flow. 1. Gate valves Bon 機罩 Yoke 機架 The typical gate valve consists of a gate, body, seating area, stem, bon, packing, stuffing box, packing gland, and hand wheel. The gates are sized to fit the inside diameter of a pipe. ? 42 Chapter 2. Valves Very little restriction occurs when it is in the open position. 1. Gate valves ? Size: from ” to several feet. ? Path: from “ wide open” to “ pletely shut” . ? Should not be used to throttle flow. The gate can be wedge shaped or may consist of parallel discs. The gate is placed directly in the path of a process flow when it is shut and is lifted pletely out of the way when open. ? 43 Chapter 2. Valves Gate valves The body is the largest part of the valve. The body can be connected to the process piping in three ways: flanges, threaded, or welding. The seating consists of two fixed surfaces or rings inside the body of the valve that the gate closes against to stop flow. The seating area falls into two categories: replaceable or fixed. The stem is a long, slender shaft attached to the gate, bushing, or wheel. When the hand wheel is turned, it transmits rotational energy to the stem, causing it to rise to open or lower to close. The bon provides a housing for the gate or disc when it is lifted out of the process flow. It is attached to the body permanently by welding or temporarily by threading or bolts. ? 44 Chapter 2. Valves 2. Globe valves ?Globe val