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A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, or inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal. An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Heart valves are essentially inlet and outlet check valves for the heart ventricles, since the ventricles act as pumps. ==Technical terminology== Cracking pressure — the inlet pressure at which the first indication of flow occurs (steady stream of bubbles). Reseal pressure — the pressure at which there is no indication of flow. Back pressure — the differential pressure between the inlet and outlet pressures 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Check valve」の詳細全文を読む スポンサード リンク
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