![]() ![]() 20 kPa means there is no pressure, 100 kPa means there is full range pressure (can be varied by the transmitters calibration points). A pressure transmitter will monitor the pressure in the vessel and transmit a signal from 20–100 kPa. For example, a valve could be controlling the pressure in a vessel which has a constant out-flow, and a varied in-flow (varied by the actuator and valve). The valves input is the "control signal." This can come from a variety of measuring devices, and each different pressure is a different set point for a valve. Larger forces are required in high pressure or high flow pipelines to allow the valve to overcome these forces, and allow it to move the valves moving parts to control the material flowing inside. This pressure is transferred to the valve stem, which is connected to either the valve plug (see plug valve), butterfly valve etc. However, the resulting forces required of the stem would be too great and cause the valve stem to fail. On 100 kPa input, you could lift a small car (upwards of 1,000 lbs) easily, and this is only a basic, small pneumatic valve. These pressures are large enough to crush objects in the pipe. Having a larger piston can also be good if air supply is low, allowing the same forces with less input. The larger the size of the piston, the larger the output pressure can be. Valves require little pressure to operate and usually double or triple the input force. It keeps the air in the upper portion of the cylinder, allowing air pressure to force the diaphragm or piston to move the valve stem or rotate the valve control element. The motion can be rotary or linear, depending on the type of actuator.Ī Pneumatic actuator mainly consists of a piston or a diaphragm which develops the motive power. ![]() A pneumatic control valve actuator converts energy (typically in the form of compressed air) into mechanical motion. ![]()
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