Due to the needs of compressor structure, manufacturing, assembly, operation, etc., certain parts of the cylinder are left with a certain space or gap, which is called the clearance volume. (Also known as harmful capacity or storage of qi).
The compressor has a clearance volume in the following parts:
1. When the exhaust stroke of the piston movement ends, the gap between the end face of the piston and the end face of the cylinder;
2. The clearance between the cylinder mirror surface and the outer circle of the piston (from the end surface to the first piston ring);
3. The volume formed by the passage from the air valve to the cylinder volume.
The volume of the air valve itself, such as the channel of the valve seat, the spring hole, etc. (the channel volume accounts for the largest proportion, the annular gap has a very small value) the clearance volume of the compressor, some are structural needs, and some are inevitable. For example, when the piston moves to the exhaust end position, the gap between its end face and the cylinder end face is mainly due to the following factors:
1. When the piston moves periodically, due to the heat generated by friction and compression of the gas, the piston is heated and expanded, resulting in radial and axial elongation. In order to avoid collision accidents between the piston and the cylinder end surface and the piston and the cylinder wall, it is used The clearance volume is eliminated.
2. For compressed gas containing water droplets, the water droplets may aggregate during compression. In this case, the clearance volume can prevent water hammer due to water incompressibility. 3. Manufacturing accuracy and parts assembly always deviate from requirements. The moving parts may loosen during the movement, which increases the gap between the joint surfaces and the total size of the parts.
The clearance volume formed by the passage from the air valve to the cylinder volume is mainly due to the air valve arrangement unavoidable.
When the compressor is working, the clearance volume reduces the volume of gas sucked by the intake valve, and the corresponding discharge volume is reduced. Therefore, when designing the cylinder, the effect of clearance volume on the discharge volume should be considered in advance. When designing the compressor, taking into account the productivity, manufacturing, assembly and safe operation, the clearance volume should be as small as possible. But sometimes in order to adjust the piston force, the clearance volume is increased accordingly, which is often encountered when designing a counter-acting compressor.