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Engine valve

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  • Valves are used to control gas flow to and from cylinders in automotive internal combustion engines. The most common type of valve used is the poppet valve. The valve itself consists of a disc-shaped head having a stem extending from its centre at one side. The edge of the head on the side nearest the stem is accurately ground at an angle usually 45 degrees, but sometimes 30 degrees, to form the seating face. When the valve is closed, the face is pressed in contact with a similarly ground seat.
  • The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve leakage will occur which will adversely affect the engine compression ratio and therefore the engine efficiency, performance (horsepower), exhaust emissions, and engine life.
  • Valve seats are often formed by first press-fitting an approximately cylindrical piece of a hardened metal alloy, such as Stellite, into a cast depression in a cylinder head above each eventual valve stem position, and then machining a conical-section surface into the valve seat that will mate with a corresponding conical-section of the corresponding valve.
  • Valves are subject to both thermal and mechanical loads,the latter being applied by the springs and actuating gear. All these loads are so severe as to justify an assertion that the valves are the most heavily loaded components in an engine. Exhaust valves , in particular , operate for long periods at high temperatures 700-800.
  • Valve seats are an extremely important part of a cylinder head because the seats cool and seal the valves. They also support the valve when it closes, which affects both valve train geometry and valve lash. If a seat is damaged, cracked, loose, receded or too badly worn to be recut or reground, it can cause a variety of problems: loss of compression, valve burning, valve failure, valve train wear and breakage, even head and valve damage if the seat comes loose.
  • Seats should not be replaced until the head has been thoroughly cleaned and inspected. This includes checking for cracks (especially around and near the valve seats) and checking the deck surface and cam bore for straightness. Any welding and/or straightening that may be needed must be done before remachining the valve seats or installing new inserts.
  • Also, the valve guides should be replaced or reconditioned before the seats are machined. Concentricity between the seat and guide is absolutely essential for a proper alignment, good compression and long term valve durability.
  • The cylinder head must be dimensionally and geometrically within specifications before seat counterbores are machined. That includes cylinder head thickness, valve guide clearances, concentricity and perpendicularity. There should be no warping, twisting or any type of misalignment anywhere in the head.
  • PEP-PRO Engine Valves were introduced to the Australian market in 1985, in response to a growing demand from the performance aftermarket industry. The initial launch with Chevrolet, Datsun, Ford and Holden valves has seen the Pep-Pro brand become the choice of many engine builders across Australia.
  • The automotive parts industry has undergone a significant change in the recent past. There has been a considerable shift in cars and components, production methods and materials. Driven by expanding demand in the Asian economies and new product developments, worldwide pistons, piston rings and engine valves market is forecast to reach 2.5 billion units by 2010.
  • Engine valves market is forecast to witness the fastest growth at a CAGR of over 3% over the period 2000-2010. Most engine subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine. The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The camshaft has lobes on it that move the valves up and down.

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