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.

因此活塞環是工作在高溫、高壓條件下的。尤其是道氣環，承受的溫度，潤滑條件也更差，為了保證它具有和其它幾道環相同或更高的耐用性，常常將道氣環，的工作表面進行多孔鍍鉻處理。多孔鍍鉻層硬度高，并能貯存少量的潤滑，以改善潤滑條件，使環的壽命提高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.

近年來，摩托車發動機大多采用長度短于缸徑的活塞，這種活塞的頭部在上行程轉到下行程時會產生擺動現象，使活塞環外圓的上下邊緣緊緊地與缸壁接觸，導致活塞環的棱緣加載而形成刮傷。為避免這種異常現象，一般將道氣環外圓制成圓弧狀，以其上、下端面的邊緣角不觸及缸壁，并且易于發動機的初期磨合，這種氣環稱為桶面環，為目前高功率高轉速的內燃機所采用。

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.

盡管當今制造技術非常精細，零部件差亦控制在更小范圍，但因其材料、熱處理及裝配后的機械變形，汽缸內的氣密總有極個別泄漏點存在，這就需要發動機在使用初期進行良好的磨合及啟動后適當的預熱來逐漸消除摩擦副的凹凸不平點。

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.

倘若由于多種原因引起汽缸的密封不良時，會引起壓縮壓力下降和燃燒氣體的竄漏，高壓高溫氣體將穿過缸壁與活塞環之間的微小空隙，由此而引起的故障是破壞了活塞環與缸壁之間的所必需的油膜，以致形成了金屬之間直接接觸的干磨擦狀態，從而導致了因干磨擦而燒傷的拉傷活塞、活塞環和汽缸，使發動機產生異常磨損。

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.

泄漏的高溫氣體竄入曲軸箱使機油變質和產生硬質油泥，使活塞環發生粘著等故障。由此看來，確保活塞環在汽缸內的氣密性關重要，來不得任何的泄漏。

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.