Commonly used valves in refrigeration systems include globe valves, safety valve
s, pressure gauge valves and check valve
s. (1) Stop valve The stop valve is the most used valve in the refrigeration system. It is installed on refrigeration equipment and pipelines to open and close the refrigerant channel. ①Compressor shut-off valve This valve is divided into suction shut-off valve and exhaust shut-off valve, which are mostly used in small and medium-sized open-type compressors. The suction shut-off valve and the exhaust shut-off valve are respectively connected with the suction chamber and the air chamber of the cylinder head to control the flow and on-off of the refrigerant in the system, which is convenient for the adjustment and maintenance of the compressor and the refrigeration system. The structure is shown in Figure 3-47. There are three passages on the valve body of the compressor stop valve, passage A is connected to the suction chamber or discharge chamber of the compressor; passage D is connected to the suction pipe (for suction valve) or exhaust pipe (for exhaust valve); Bypass C is a multi-purpose channel, through which it can be connected to pressure gauges, pressure difference controllers, etc., or to perform operations such as vacuuming, charging refrigerant, and replenishing lubricating oil during maintenance. When the channel is not in use, it should be blocked with a steel hexagonal screw plug. In order to prevent the refrigerant from leaking through the valve stem and the valve body, they are all filled with packing seals with compression screws on them. If leakage is found along the stem, the packing screw can be tightened appropriately to improve the sealing performance. Unscrew the bonnet and turn the valve stem to change the open and close state of the three channels. ②The shut-off valve in the piping system The structure of the shut-off valve in the piping system is basically the same as the compressor shut-off valve, but there is no multi-purpose channel. According to the type of refrigerant, the shut-off valve is divided into ammonia and fluorine shut-off valves; according to its shape, it is divided into straight-through and right-angle shut-off valves. The valve used in the refrigeration system requires high sealing performance and has an inverting device. When the valve is fully opened, the valve stem rises to the highest position, and the upper end surface of the valve core and the stuffing box seat are in close contact and pressed to prevent the refrigerant from escaping from the packing. Refrigerators using freon, because freon has strong permeability, so fluorine stop valve generally does not use a hand wheel, but use a wrench to adjust the opening of the valve, and then use the bonnet to all the stem and stuffing box Cover it to reduce refrigerant leakage in the system. The structure of the fluorine stop valve is shown in Figure 3-48. Most of the small Freon valves are made of copper alloy, which has good sealing and anti-corrosion ability. The structure of the ammonia stop valve is shown in Figure 3-49. The valve body is made of high-strength cast iron, and the sealing material of the valve head is made of Babbitt alloy and polytetrafluoroethylene. The stem is made of high-quality carbon steel. In order to prevent the stem from rusting, some stems are nitridated, and the stem seal is filled with asbestos impregnated graphite packing, and some valves are made of PTFE with V-shaped seals. Ring, it has a better sealing effect. The valve switch is also relatively light. (2) Safety valve Safety valve is a protection device for pressure vessels. When the refrigerant pressure in the container exceeds the specified value, it can automatically eliminate the excess pressure and automatically close when the pressure returns to the specified value to ensure the safe operation of the equipment. The condenser, accumulator, low-pressure circulating accumulator, ammonia separator, and intercooler in the refrigeration system are all equipped with safety valves. The structure of the safety valve adopts a spring slightly open type, as shown in Figure 3-50. It is composed of valve body, valve seat, valve disc (spool), steel ball, positioning washer, spring, adjusting bolt, valve cover, lock nut, nut and other parts. It relies on the force of the compressed spring to balance the pressure that the valve disc is detached from the valve seat to achieve the purpose of sealing and opening. The opening height of the micro-opening valve is 1/20~1/4 of the diameter of the throat of the valve seat. The opening height changes gradually with pressure changes, and there is no sudden jump and sudden closing action. The safety alarm take-off pressure is adjusted with adjusting bolts according to the requirements of the relevant equipment. After adjustment, the valve cap is fixed and sealed with a locking female. The lower end surface of the valve disc is embedded with a PTFE plastic tight ring (or Babbitt alloy). When the pressure of the container is greater than the adjusted spring force, the valve disc is released. The valve seat and the valve seat have a small hole on the sealing line. When the pressure drops below the take-off pressure, the spring force is greater than the container pressure, and the valve flap is gradually pressed down on the valve seat to seal. There is a steel ball between the valve disc and the positioning washer, which can accurately reset when it is opened and closed. (3) Pressure gauge valve The pressure gauge valve is the valve gauge installation and maintenance of special control pressure gauges on refrigeration equipment, regulating stations and ammonia refueling stations. The structure of the pressure gauge valve and the shut-off valve is roughly the same. It is divided into the pressure gauge valve for ammonia (Figure 3-51) and the pressure gauge valve for fluorine (Tian 3-52). Because the purpose of the valve is different from that of the stop valve, the structure is slightly different. The pressure indicated by the diameter is small, usually the nominal diameter is DNu003d3~4mm, and the outlet end of the valve has an internal thread M20×1.5 that is specially threaded with the pressure gauge. . The pressure gauge valve for fluorine and some pressure gauge valves for ammonia does not have a thin diaphragm on the inlet and outlet channels of the valve body, and it is controlled by a steel ball installed on the valve head. (4) Check valve Check valve, also known as check valve or one-way valve, is a door that automatically opens and closes by the pressure difference between the front and back of the valve. The refrigeration system pipeline is equipped with a check valve to prevent the refrigerant from flowing back. The structure of the check valve has two major types: lift type and swing type. The lift check valve is used in the refrigeration system.
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