The piston ring is the only one that moves in three directions among all engine parts. (i.e. axial movement, radial movement and circumferential rotation movement), it is also the most demanding part in service conditions. At the moment of explosion, the gas temperature of engine combustion chamber can reach 2000 ℃ - 2500 ℃, the average explosion pressure can reach 50kg / cm ~ 2, and the temperature of piston head is not lower than 200 ℃. Piston is reciprocating, its speed and load are very large.

因此活塞环是工作在高温、高压条件下的。尤其是道气环，承受的温度，润滑条件也更差，为了保证它具有和其它几道环相同或更高的耐用性，常常将道气环，的工作表面进行多孔镀铬处理。多孔镀铬层硬度高，并能贮存少量的润滑，以改善润滑条件，使环的寿命提高2－3倍。

Therefore, the piston ring works under high temperature and high pressure. In particular, the first ring bears the highest temperature and the worst lubrication condition. In order to ensure that it has the same or higher durability as other rings, the working surface of the first ring is often treated with porous chromium plating. The porous chromium plating layer has high hardness and can store a small amount of lubrication, so as to improve the lubrication condition and increase the service life of the ring by 2-3 times.

近年来，摩托车发动机大多采用长度短于缸径的活塞，这种活塞的头部在上行程转到下行程时会产生摆动现象，使活塞环外圆的上下边缘紧紧地与缸壁接触，导致活塞环的棱缘加载而形成刮伤。为避免这种异常现象，一般将道气环外圆制成圆弧状，以其上、下端面的边缘角不触及缸壁，并且易于发动机的初期磨合，这种气环称为桶面环，为目前高功率高转速的内燃机所采用。

In recent years, most of the motorcycle engines use the piston whose length is shorter than the cylinder diameter. The head of the piston will swing when the up stroke turns to the down stroke, which makes the upper and lower edges of the outer circle of the piston ring tightly contact with the cylinder wall, causing the edge of the piston ring to load and form scratches. In order to avoid this abnormal phenomenon, the outer circle of the first gas ring is generally made into an arc shape. The edge angle of the upper and lower end faces does not touch the cylinder wall, and it is easy for the initial running in of the engine. This kind of gas ring is called barrel face ring, which is adopted by the current internal combustion engines with high power and high speed.

尽管当今制造技术非常精细，零部件差亦控制在更小范围，但因其材料、热处理及装配后的机械变形，汽缸内的气密总有极个别泄漏点存在，这就需要发动机在使用初期进行良好的磨合及启动后适当的预热来逐渐消除摩擦副的凹凸不平点。

Although today's manufacturing technology is very fine, and the difference of parts is controlled to a minimum, due to its material, heat treatment and mechanical deformation after assembly, there are always very few leakage points in the air tightness of the cylinder, which requires the engine to carry out good running in at the early stage of use and proper preheating after starting to gradually eliminate the uneven points of the friction pair.

倘若由于多种原因引起汽缸的密封不良时，会引起压缩压力下降和燃烧气体的窜漏，高压高温气体将穿过缸壁与活塞环之间的微小空隙，由此而引起的故障是破坏了活塞环与缸壁之间的所必需的油膜，以致形成了金属之间直接接触的干磨擦状态，从而导致了因干磨擦而烧伤的拉伤活塞、活塞环和汽缸，使发动机产生异常磨损。

If the sealing of the cylinder is not good due to various reasons, it will cause the decrease of the compression pressure and the leakage of the combustion gas. The high pressure and high temperature gas will pass through the tiny gap between the cylinder wall and the piston ring. The resulting failure is to destroy the necessary oil film between the piston ring and the cylinder wall, resulting in the formation of a dry friction state of direct contact between the metals, resulting in the dry wear The piston, piston ring and cylinder are scratched and burned, resulting in abnormal wear of the engine.

泄漏的高温气体窜入曲轴箱使机油变质和产生硬质油泥，使活塞环发生粘着等故障。由此看来，确保活塞环在汽缸内的气密性关重要，来不得任何的泄漏。

The leakage of high temperature gas into the crankcase makes the engine oil deteriorate and produce hard sludge, so that the piston ring adhesion and other faults. From this point of view, it is important to ensure the air tightness of the piston ring in the cylinder to prevent any leakage.