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The upper part of the valve stem, within the rocker box, is lubricated by oil. If this oil travels unchecked along the valve stem, engine HC emissions will become excessive. To control this, an elastomeric seal is fitted over the top of the valve guide. These may wear or stiffen with age, so are usually replaced whenever valves are removed for ...
The effective mass of a traditional valve with spring includes one-half of the valve spring mass for symmetric springs and all of the valve spring retainer mass. However, a desmodromic system must deal with the inertia of the two rocker arms per valve, so this advantage depends greatly on the skill of the designer.
The valve's body is the outer casing of most or all of the valve that contains the internal parts or trim. The bonnet is the part of the encasing through which the stem (see below) passes and that forms a guide and seal for the stem. The bonnet typically screws into or is bolted to the valve body. Valve bodies are usually metallic or plastic.
An automatic control valve consists of three main parts in which each part exist in several types and designs: Valve actuator – which moves the valve's modulating element, such as ball or butterfly. Valve positioner – which ensures the valve has reached the desired degree of opening. This overcomes the problems of friction and wear.
Cutaway of a dual overhead camshaft engine 1969 AMC V8 overhead valve engine. The rocker cover has been removed, so the pushrods, rocker arms, valve springs, and valves are visible. A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. [1]
Newer models usually incorporate a spring-loaded valve that lifts and allows pressure to escape as pressure in the vessel rises. Some pressure cookers will have a quick release setting on the pressure regulator valve that will, essentially, lower the spring tension to allow the pressure to escape at a quick, but still safe rate.
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Replacing a valve stem. A valve stem is a self-contained valve that opens to admit gas to a chamber (such as air to inflate a tire), [1] and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, [2] [3] or both, to prevent the gas from escaping.