Which is better, high pressure or low pressure chamber compressor? What are the common faults?

In the refrigeration system, the compressor is the "heart" of the energy cycle. High-pressure chamber and low-pressure chamber compressors are two major technical schools. Due to their unique design and operating characteristics, they have formed differentiated applications in many fields. This article will analyze the structure, performance, operation and maintenance, and provide decision-making reference for engineers.

1. Differentiated design of cavity structure and operating mechanism

Low-pressure cavity compressor (taking COPELAND as an example)
Adopting a "motor rear-mounted" design, the motor assembly is located in the exhaust side area. The exhaust pressure endured by the shell is transmitted to the bearing support structure through the mechanical seal system, forming a stable force distribution. The trapezoidal buffer cavity (volume accounting for 25%-30%) set up in the suction section realizes airflow velocity gradient control through the Venturi effect, reducing the intake airflow velocity from 8-12m/s to 2-4m/s, effectively suppressing the propagation of pulsation waves. This design enables the pressure fluctuation amplitude during the compression process to be controlled within ±5%.

2. Compression characteristics of high and low pressure chambers

Low pressure chamber compressor features
Excellent suction buffering: The large-volume suction buffer design is like covering the compressor with a layer of "shock-absorbing armor", which can effectively reduce airflow pulsation and significantly improve operation stability.
Excellent motor environment: Working in a low-temperature and low-voltage environment can greatly reduce the thermal stress and electrical losses of the motor, effectively extend the service life of the motor and reduce the probability of failure.
Easy to manufacture and use: Most of the shell is in a low-pressure state, which reduces the requirements for air tightness and mechanical strength. It not only reduces the manufacturing difficulty, but also reduces the cost. In addition, it has strong resistance to liquid impact and impurities, and can adapt to various complex working environments.
Suction preheating affects efficiency: The suction preheating phenomenon is more obvious, causing the refrigerant specific volume to increase and the volumetric efficiency to decrease, thereby limiting the cooling capacity.
Large exhaust vibration: The exhaust buffer volume is small, and the exhaust is like "turbulent waves", which will produce greater noise and vibration, affecting the comfort of equipment operation.
Lubrication and sealing are difficult: [Source of this article: Refrigeration Encyclopedia Official Account] The oil volume control requirements are high, and liquid refrigerant may destroy the lubricating oil film and aggravate bearing wear. At the same time, the coexistence of high and low pressure chambers increases the difficulty of sealing and can easily cause refrigerant leakage problems.

High pressure cavity compressor fault diagnosis
Suction noise problem: If the suction noise is large, check whether the suction buffer device is intact, whether it is blocked or damaged, and evaluate the rationality of the suction duct design [Source of this article: Refrigeration Encyclopedia Official Account].
Anti-liquid hammer failure: When liquid hammer occurs, such as abnormal impact sounds inside the compressor, it is necessary to check the working status of the evaporator and expansion valve to prevent refrigerant droplets from entering the compressor.
Motor failure: When the motor overheats, the winding insulation resistance decreases, or the current is abnormal, it is necessary to consider the impurities in the suction gas and the heat dissipation of the motor, and check the suction filter and motor cooling system.
High-pressure chamber and low-pressure chamber compressors each have their own advantages and disadvantages. In practical applications, reasonable selection should be made based on specific working conditions and needs. When equipment fails, through careful observation and analysis of the fault phenomenon, we can accurately determine the fault and damage, repair the equipment in time, and ensure the efficient and stable operation of the refrigeration system!

Shanghai KUB Refrigeration Equipment Co., Ltd.

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