First, a high-pressure liquid refrigerant throttling, ensure that the pressure between the condenser and the evaporator of the difference, so that the liquid refrigerant in the evaporator at low pressure evaporated under heat required to achieve the purpose of cooling down; at the same time, so that gas refrigerant in the condenser at a given high pressure decentralized heat and condensation.

Second, adjusting the flow of refrigerant to the evaporator, in order to adapt to changes in the heat load of the evaporator, the refrigeration apparatus more efficient operation.

Controlled throttle mechanism for entering the evaporator function of the liquid refrigerant mass flow rate, it is sometimes also called flow control mechanism. Further, it is the high-pressure liquid refrigerant throttling the refrigerant, an expansion valve bore to a wet vapor of boiling, it is also called throttling or expansion valve. Throttle mechanism commonly used are the following: Manual expansion valve, float expansion valve, thermal expansion valve and capillary

A manual expansion valve

And the general structure of the manual shut-off valve expansion valve is similar, except that it is a needle-shaped spool having a cone or cone-shaped notch Ⅴ. The stem has fine thread, while rotating the hand wheel, can open the valve slowly increase or a small base, to ensure good regulation.

Its distinguishing feature is perishable. Management may be based on the impact of the evaporator heat load changes and other factors, to manually adjust the expansion valve opening, therefore, management cumbersome and requires a high experience in the recent use of automatic expansion valve, and an expansion valve manually only on the bypass pipe as a supporting role.

Second, the expansion valve float

Float expansion valve used for flooded evaporator, the evaporator requires to maintain a certain level height, is in line with the characteristics of the float expansion valve.

According to the flow of refrigerant liquid formula different situations, it can be divided into straight and non-straight two, they have their own advantages and disadvantages. Expander straight-through valve supplying vaporized liquid, first of all through the float chamber, then enter through tube evaporator fluid balance, so it has the characteristics of simple structure, but the float chamber level fluctuations, the impact on the valve body force is large, easy to damage the valve body; outside at times, but also requires a large diameter balance pipe. Non-straight-float expansion valve, the valve bodies float outdoor throttling refrigerant does not pass through the float chamber, but directly into the evaporator along the pipe, so that the float chamber smooth surface, but in the construction and installation complex.

Third, the thermal expansion valve

And the float expansion valve is different, it is not by controlling the level, but to control the evaporator outlet superheat the gaseous refrigerant into the evaporator for controlling the flow of refrigerant. Because part of the evaporator area must be used to superheat the gaseous refrigerant, it is widely used in the air conditioning or cryogenic systems (especially freon refrigeration system) of all non-flooded evaporator.

Thermal expansion valve due to balance in different ways, or that pressure to evaporation in the lower die cavity in different ways, may have internal balance and external balance type two.

Capacity is an important characteristic parameter thermal expansion valve, so we must understand the impact of the capacity of the main prisoners factors: 1. Pressure difference before and after the expansion valve 2. 3 evaporation temperature. The refrigerant subcooling.

Thermal expansion valve installation location must be close to the evaporator where the body should be upright, not tilted, but not installed upside down. Is to install temperature-sensitive packages, which typically wrapped around the intake pipe, close to the wall, wrapped tightly, contact points should be cleaned of scale, exposing the metal pipe character, it can be coated with a layer of aluminum paint as a protection, if necessary layer, to prevent rusting.

Fourth, the capillary

Capillary is based on "much easier than liquid gas through" this principle. It depends on the flow capacity and the capillary and the state of the refrigerant inlet of the capillary geometry. With the ability to increase fluid supply inlet pressure to improve capillary, capillary length increased diameter narrowing accordingly so that the liquid supply capacity is reduced. Capillary has its advantages, simple structure, no moving parts, low prices, the use of the system it may not be installed accumulator; less charged refrigerant; and after the compressor stops running, the condenser and the evaporator pressure can be quickly and automatically balance, reduce the load when you start the motor. It exists disadvantage is its poor performance regulating its flow capacity and, with fluctuations in operating conditions can not be adjusted.

Using a capillary should note the following:

1. Ling agent system can not be there in the high-pressure side of the refrigeration cycle pipeline easily gather.

2. Capillary filling amount of refrigerant in the refrigeration system must be correct.

3. Capillary inlet section should be installed 200-300 mesh / inch filter (net) to prevent dirt from clogging the hole.

4. When a few capillaries in parallel, in order to make uniform flow, followed by the use of dispensers.

5. Butyl rubber and other materials should be wrapped in an outer capillary tube for acoustic shock.