Screw refrigeration compressors and piston refrigeration compressors have the same gas compression method, both belonging to volumetric compressors, which means they both compress gas through changes in volume. The difference lies in the way these two compressors achieve changes in working volume.

Screw refrigeration compressors are divided into single screw compressors and twin-screw compressors. The twin-screw compressor utilizes two screws with spiral grooves placed inside the body to mesh and rotate, as well as their cooperation with the inner walls of the body and the suction and exhaust end seats, causing changes in the volume between teeth, thus facilitating the process of gas suction, compression, and discharge.

Chassis:It is generally a split type, consisting of three parts connected by bolts: the body, the suction end seat, and the exhaust end seat. The cross-section of the internal cavity of the body is in the shape of a cross 8 intersecting double circles, which is suitable for the outer cylindrical surfaces of the two meshing rotors placed inside it.

1、 Principle of Four Stage Capacity Adjustment for Screw Compressor in High and Low Temperature Impact Test Chamber

The four stage volume control system consists of a volume control slide valve, three normally closed solenoid valves, and a set of volume control oil pressure pistons, with adjustable ranges of 25% (used during start-up or shutdown), 50%, 75%, and 100%.

The principle is to use an oil pressure piston to push the volume adjustment slide valve. When there is partial load, the volume adjustment slide valve moves to bypass some refrigerant gas back to the suction end, reducing the refrigerant gas flow rate to achieve partial load function. When the machine is stopped, the force of the spring returns the piston to its initial state.

When the compressor is running, the oil pressure starts to push the piston, and the positioning of the oil pressure piston is controlled by the action of the solenoid valve, which is controlled by the inlet (outlet) water temperature switch of the system evaporator. The oil that controls the volume adjustment piston is sent from the oil storage tank of the casing in a differential pressure manner. After passing through the oil filter, it is limited by a capillary tube before being sent to the hydraulic cylinder. If the oil filter or capillary tube is blocked, it will cause the volume adjustment system to operate improperly or fail. Similarly, if the volume adjustment solenoid valve fails, a similar situation can also occur.

(1) 25% start-up operation

When starting the compressor, the load must be reduced tolowEasy to start. So when SV1 is activated, the oil is directly bypassed back to the low-pressure chamber, while the bypass space of the volume adjustment slide valve is the largest. At this time, the load is only 25%. After starting, the compressor can start gradually loading. The general starting time for 25% load operation is about 30 seconds.

(2) 50% load operation

With the execution of the startup program or the action of the set temperature switch, the SV3 solenoid valve is electrically connected, and the volume adjustment piston moves to the oil bypass port of the SV3 valve, driving the position of the volume adjustment slide valve to change. Part of the refrigerant gas returns to the low-pressure chamber through the screw bypass circuit, and the compressor operates at 50% load.

(3) 75% load operation

When the system startup program is executed or the set temperature switch is activated, a signal is sent to solenoid valve SV2. SV2 is electrically connected, and the volume adjustment slide valve moves to the SV2 bypass port position under the action of oil pressure. The oil flows back to the low-pressure side from the SV2 bypass port, and some refrigerant gas flows back to the low-pressure chamber from the screw bypass port. The compressor displacement increases (decreases), and the compressor operates at 75% load.

(4) 100% full load operation

After the compressor is started or the freezing water temperature is higher than the set value, SV1, SV2, and SV3 are not powered, and oil directly enters the hydraulic cylinder to push the displacement adjustment piston forward. The displacement adjustment piston drives the displacement adjustment slide valve to move, gradually reducing the refrigerant gas bypass port until the displacement adjustment slide valve is pushed to the bottom. At this time, the compressor runs at 100% full load.

2、 High and low temperature impact test chamber screw compressor stepless capacity adjustment system

The basic principle of the stepless capacitance adjustment system is the same as that of the four stage capacitance adjustment. The difference lies in the control application of the solenoid valve. The four stage capacity control uses three normally closed solenoid valves, while the multi-stage capacity adjustment control uses one normally open solenoid valve and one or two normally closed solenoid valves to control the opening and closing of the solenoid valves to determine the loading or unloading of the compressor.
(1) Capacity adjustment range of high and low temperature impact test chamber: 25%~100%.

By using a normally closed solenoid valve SV1 (controlling the oil discharge path) to ensure the compressor starts at low loads and a normally open solenoid valve SV0 (controlling the oil inlet path), SV1 and SV0 can be controlled to be powered or not to be powered according to the load requirements to achieve the effect of controlling capacity adjustment. This continuous control of capacity adjustment can be achieved between 25% and 100% capacity to achieve stable output. The recommended action time for solenoid valve control is in the form of pulses, which can be adjusted according to actual conditions.

Schematic diagram of seamless capacity adjustment process (1)When the compressor is started, SV1 needs to be powered on to guide the refrigerant oil in the volume adjustment system back to the low-pressure end of the compressor through the SV1 oil circuit (SV0 is powered off). The oil piston, due to the force of the internal spring, drives the volume adjustment slide valve to the 25% load position. After starting, all solenoid valves are powered off, allowing the compressor to operate at 100% loadIn steady state, SV1 is continuously powered off, while SV0 is continuously powered on to maintain stable cooling output; When the environmental load changes, control the combination of power on and off of SV1 and SV0, adjust the output cooling capacity of the compressor to meet the actual load requirements of the environment; When the environmental load increases, SV0 briefly (pulse) loses power, and an appropriate amount of refrigerant oil flows into the hydraulic cylinder through SV0, causing the volume adjustment slide valve to move in the direction of increasing the cooling capacity; When the environmental load decreases, SV1 is briefly (pulsed) energized, and an appropriate amount of refrigerant oil flows out of the hydraulic cylinder through SV1, causing the volume adjustment slide valve to move in the direction of reducing the cooling capacity.Action diagram of electromagnetic valve for infinite capacity adjustment (25%~100%)Attention: The ON/OFF in the above table represents the power on/off of the solenoid valve, and "pulse" represents the pulse power supply(2) Capacity adjustment range: 50%~100%
To prevent the refrigeration compressor motor from running at low load for a long time (25%), which may cause high motor temperature or liquid compression due to the excessive capacity of the expansion valve, the low capacity adjustment of the compressor can be controlled above 50% load when designing a stepless capacity adjustment system.Using a normally closed solenoid valve SV1 (controlling oil circuit bypass) to ensure that the compressor starts at a low 25% load; In addition, a normally open solenoid valve SV0 (controlling the oil inlet passage) and a normally closed solenoid valve SV3 (controlling the oil outlet passage) are used to limit the operation of the compressor within the range of 50% to 100%. SV0 and SV3 are controlled to be powered or not as needed to achieve continuous and uninterrupted control of capacity regulation.

Suggestion for solenoid valve control actuation time: pulse form for about 0.5-1 second, adjust according to actual situation.
When the compressor starts at 25%, SV1 needs to be powered on in order to pass the refrigeration oil from the hydraulic cylinder back to the low-pressure end of the compressor through the SV1 oil circuit (SV0, SV3 are powered off). Therefore, the capacity adjustment slide valve is maintained at the 25% load position due to the internal spring force of the oil piston; After startup, SV0, SV1 are powered off and SV3 is powered on, causing the compressor to run continuously at 50% load for 180 seconds. Then, all solenoid valves are powered off, allowing the compressor to run at 100% load.
When stable, SV3 is continuously powered off, while SV0 is continuously powered on to maintain stable cooling output; When the environmental load changes, control the combination of power on and off of SV0 and SV3, adjust the output cooling capacity of the compressor to meet the actual load requirements of the environment; When the environmental load increases, SV0 briefly (pulse) loses power, allowing a small amount of refrigerant oil to flow into the hydraulic cylinder, causing the volume adjustment slide valve to move in the direction of increasing the cooling capacity; When the environmental load decreases, SV3 is briefly (pulsed) energized, allowing a small amount of refrigerant oil to flow out of the hydraulic cylinder through SV3, causing the volume adjustment slide valve to move in the direction of reducing the cooling capacity.Electromagnetic valve action table for infinite capacity adjustment (50%~100%):Attention The ON/OFF in the above table represents the power on/off of the solenoid valve, and "pulse" represents the pulse power supply;