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How to overcome pressure at work? - How to overcome pressure at work?

Technical information Controls and Other Circuit Components Pressure switches

Pressure switch

Pressure in the condenser side of the system should always be limited to the maximum value and pressure control is used to stop the compressor in case of need. High pressure cut-outs, Fig. 9.3, which are set for all but the most minor systems. Where the compressor is provided with a shut-off valve, pressure must be connected to the valve. Pressure at the compressor outlet taken to one side of the bellows or diaphragm, and balanced adjustable spring. The scale of control indicates the pressure for commercial checked for accuracy and commissioning of the system.

If we overcome the spring pressure, the switch will open and stop of the compressor. The incision can also work a warning. Cut only point should be about 2 bar higher than expected in the summer working pressure, but there is a tendency to establish such control is much higher, sometimes up to 8 bar above the summer load. On this setting, the user will not receive warning of abnormal running until the fault has reached serious proportions.

Because excess pressure indicates a failure of part of the system - usually capacitor fault or incorrect closure of the valve high pressure switch must be installed manually, not automatically.

Where the refrigeration system to provide basic services that should not be interrupted, one high-pressure switch can be set at the level of prevention and operation of burglar alarm, without a stop of the compressor. The second switch, slightly above will stop the equipment, if this warning is ignored, and the pressure is obtained. All high pressure cut-outs should be checked at least once a year, for the proper installation and operation.

Abnormally low suction pressure will lead to high discharge temperature, due to the high compression ratio, and the possible malfunctions and other components. Air cooling coil can frost excessive or water chillers freeze.

Low pressure is typically installed to stop the compressor in such circumstances. Parameters can be 0.6-1.0 bar below the rated pressure boiling, but much depends on the type of system. Cut-out parameter must be greater than atmospheric pressure, if possible, to avoid the air ingress through any leaks. Abnormally low pressure cannot be disrepair and low pressure switch may be automatic reset, closing again at a pressure corresponding to a temperature slightly below that of the load.

If the installation has been shut down long enough for all the pressures to equalize and then restart, the suction pressure will pull down, below normal, until the liquid refrigerant began to circulate. In such conditions, the low pressure switch can handle. This is normal, but may require additional delay timer to prevent the frequent starting the engine compressor.

Low pressure sensor can also be used together with thermostat and electromagnetic valve of the pump-down circuit. In this method of control, and the unit will not stop the compressor, but de-energizes the solenoid valve in the liquid line to stop the refrigerant in the evaporator. The compressor continues to work and pumps down the evaporator, unless stopped at low pressure. When the thermostat needs to cool down, it opens the solenoid valve, fluid enters the evaporator and the low pressure switch will close again to restart the compressor. This method is used to ensure that the evaporator is free liquid, when the plant off. If there is a leak on the solenoid valve, it will cause the compressor to restart periodically remove excess fluid from the heat exchanger (see Fig. 9.4). The pressure relay, also made in miniature encapsulated versions mostly, pre-configured for use in integrated chain management.....

 
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