Getting the Power to ControlWritten by Thomas Yoon
One of advantages of using machines to control processes for you is that you can harness tremendous amounts of power and energy which humans do not possess.By a flick of a switch, huge sliding flood gates can move to allow large quantities of water to flow out of a dam. With just a slight twist on a handle, supertankers weighing hundreds of thousands of tons are able to turn because of corresponding rotation of huge rudders. Similarly, processes operating valves can be remotely operated to control flow, temperatures, pressures and so on. All these final control elements - flood gates, rudder, valves - must be operated by actuators. The function of actuator is to move to control elements in processes. In order to move actuator, there must be a medium for transmitting required power or action. All actuators are mechanical in nature. The common means of transmitting power are: pneumatic (air), hydraulic (fluid), and electrical (motors). The actuators must be designed to work for that medium. There are several advantages and disadvantages for choosing a particular medium. For example, pneumatic actuators are particularly useful when atmosphere contains flammable gases. By using pneumatic actuators, there is very little chance that a spark can be generated to cause a fire. However using air for actuating may be more expensive to install and to maintain.
| | Mechanical Seals for Zero LeakageWritten by Thomas Yoon
A centrifugal water pump contains a few basic components as follows:1) The housing for containing water. 2) The impeller attached to a rotating shaft that moves water. 3) The coupling that transmits rotating action of a motor (or other prime movers) to pump shaft. 4) The seal between housing and rotating shaft. 5) The bearings for ensuring that shaft turns smoothly. 6) The inlet and outlet ports for channeling water flow through pump. In order for a pump to work, pump impeller must generate pressures inside pump housing. The seal between housing and rotating shaft plays a critical role in making pump work. One of most common ways of sealing a rotating pump shaft is by using mechanical seals. The 3 components of a mechanical seal are: 1) The rotating component that moves together with rotating shaft. 2) The stationary component that is fixed to pump housing. 3) The spring that presses rotating component onto stationary component axially. Rotating Component This is a ring, usually consisting of 2 types of materials - a soft carbon piece with a highly polished axial surface, and a rubber material or o-ring that is able to grip shaft for sealing against water leak through shaft surface.
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