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Boiler Operator's Handbook
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
Small compressors are started under load. To allow larger compressors to get up to speed before starting to pump refrigerant, unloading systems are used. Unloading a cylinder is accomplished with a pin that pushes up against each suction valve to hold it open. The pin is connected to a small cylinder containing a spring, as shown in Figure 5-8. When the compressor is shut down, the springs push the pins up to hold the valves open. After the compressor gets up to speed, the oil pump builds up pressure in the oil passages of the compressor and the small unloader cylinders to force the pins down and allow the suction valves to operate. When the unloaders operate, there will be a significant difference in the sound of the compressor as it comes up to speed. The unloaders allow a compressor to be powered by a standard duty motor instead of a high torque motor. Many modern compressors use a solenoid and spring to control the pins electronically.
Power Transmission, Brakes and Cooling Systems
Published in Iqbal Husain, Electric and Hybrid Vehicles, 2021
The gear is a simple machine used for mechanical power transmission with a mechanical advantage through increase in torque or reduction in speed. This mechanical device uses the law of conservation of energy maintaining the steady flow of power or energy, since torque times speed is power that remains constant in the transmission process. In an ideal gearbox, the motion is frictionless, and the power and energy supplied at the input point of the gear are equal to the power and energy available at the delivery point. The gearbox is not used to increase the shaft speed of an electric motor, since this means that a high-torque motor is unnecessarily designed where the size of a motor is proportional to the torque output. Therefore, the gear can be used as a torque multiplier or speed reducer. A typical gear mechnism is shown in Figure 14.3.
Refrigeration and Air Conditioning
Published in Kenneth E. Heselton, Boiler Operator’s Handbook, 2020
Small compressors are started under load. To allow larger compressors to get up to speed before starting to pump refrigerant unloading systems are used. Unloading a cylinder is accomplished with a pin that pushes up against each suction valve to hold it open. The pin is connected to a small cylinder containing a spring as shown in Figure 5-8. When the compressor is shut down the springs push the pins up to hold the valves open. After the compressor gets up to speed the oil pump builds up pressure in the oil passages of the compressor and the small unloader cylinders to force the pins down and allow the suction valves to operate. You can tell when the unloaders operate because there will be a significant difference in the sound of the compressor as it comes up to speed. The unloaders allow a compressor to be powered by a standard duty motor instead of a high torque motor. Many modern compressors use a solenoid and spring to control the pins electronically.
A review of electro-hydraulic servovalve research and development
Published in International Journal of Fluid Power, 2018
Paolo Tamburrano, Andrew R. Plummer, Elia Distaso, Riccardo Amirante
The hydraulic amplification system creates a pressure difference across the main spool end faces which is capable of moving the spool. The force developed is very high compared to a proportional valve using proportional solenoids to directly drive the spool, which results in a much faster response. The hydraulic amplification system, referred to as the first stage or the pilot stage, usually employs a torque motor, which requires low electrical input power, up to 1 or 2 W, with a required current of less than 0.2 A (Hunt and Vaughan 1996). The electrical input power is amplified in the first stage to at least 10 W of hydraulic power, and then converted by the main spool to controlling around 10 kW of hydraulic output power, thus achieving very large power magnification, with power gains of the order of 104–106 (Maskrey and Thayer 1978, Plummer 2016). A torque motor is a small electromagnetic actuator mainly composed of coils, pole pieces and an armature. In the most common type of servovalve, a nozzle-flapper valve, the armature is connected to the flapper. A non-magnetic flexure tube is used to support the flapper while separating the torque motor from the hydraulic fluid.