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行业知识

What is the clearance volume of the compressor?

Edit:Bengbu Zhengda Compressor Co., Ltd.UpDate:2022-08-10

Due to the needs of compressor construction, manufacturing, assembly, operation, etc., certain parts of the cylinder have a certain amount of space or gap, which is called the clearance volume (also called harmful volume or stored air).

The compressor has clearance volume in the following parts:

1. The gap between the piston end face and the cylinder end face at the end of the piston exhaust stroke;

2. The gap between the cylinder mirror surface and the outer circle of the piston (from the end face to a piston ring);

3. The volume formed by the passage from the valve to the cylinder volume.

The volume of the valve itself, such as the channel of the valve seat, the spring hole, etc. (the channel volume accounts for a large proportion, and the annular gap has a very small value). The clearance volume of the compressor is sometimes required by the structure, and sometimes it is difficult to avoid. For example, when the piston moves to the exhaust end position, the gap between its end face and the cylinder end face is mainly considered by the following factors:

1. When the piston moves periodically, the heat generated by friction and compressed gas causes the piston to heat and shrink, resulting in radial and axial elongation. In order to prevent the piston from colliding with the cylinder end face and the piston from getting stuck with the cylinder wall, the clearance volume is used to clear it.

2. When compressing gas containing water droplets, the water droplets may gather during compression. In this case, the clearance volume can avoid water hammer caused by the incompressibility of water.

3. Manufacturing accuracy and component assembly are always biased against requirements. Moving parts may become loose during movement, increasing the gap between the separation surfaces and the total size of the components.

The clearance volume formed by the passage from the valve to the cylinder volume is mainly difficult to avoid due to the arrangement of the valve.

When the compressor is working, the clearance volume reduces the volume of gas sucked by the intake valve, and the corresponding exhaust volume is reduced. Therefore, when designing the cylinder, the influence of the clearance volume on the exhaust volume should be considered in advance. When designing the compressor, the clearance volume should be as small as possible in consideration of productivity, manufacturing, assembly operation and other conditions. However, sometimes in order to adjust the piston force, the clearance volume is increased accordingly, which is also often encountered when designing a moving compressor.