Manual expansion valve
Manual valve expansion illustrates the main means by which the refrigerant is measured through all adjustable devices of the account. This manual valve. The speed of the refrigerant flow through the valve is determined by three things: the size of the valve orifice or opening, pressure difference through the hole, and as far valve is open. Zoom in on any of these three factors, the increase in the flow, while the decline in any will reduce the flow.
To illustrate how this metering device matches the capacity to boot the system, let's assume that we have air conditioning for cooling small commercial building which is being used air-cooled condenser. He uses hand-expansion valve as the measuring device. When the thermal load on the air conditioning system is low (say 50% of the rated load), valve manually adjusted up to half of the window. This setting allows the refrigerant to enter the evaporator at a rate that produces slightly superheated gas from the evaporator.
As the cooling load begins to grow, the valve should be opened a bit more.
If not, the evaporator will be starving, the suction pressure will drop, and overheating be excessive. As a result, system efficiency and throughput will suffer. As the cooling load is reduced, the valve must be closed slightly. If not, the evaporator will be flooded with excess liquid refrigerant, causing pressure suction grow and liquid refrigerant from the evaporator. System performance will be poor and the compressor may be damaged.
The obvious drawback to a manual valve expansion is that it makes no automatic adjustments in accordance with changes in system of cooling load. It must be opened or closed manually each time you change the load on the system. Equipment operator must be on hand at each change of the load on the system. When automatic control is required, or when the system load change often, a different type of measuring instrument is recommended. For these reasons, hands-expansion valve rarely, if ever, used today. However, it has been used in the past on large commercial or industrial jobs, and had relatively stable loads and operating engineer...