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Hi I am a fellow class 4 engineer,here to spend my free time useful to someone you can shoot all your questions on comments regarding written or orals I will try to clear my best and help you to achieve the final goal class4 .

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Crosshead, crosshead guide and shoe

Crosshead is attached on the upper part of the connecting rod, which connects the con-rod to the piston rod. The guide and the guide shoe runs on the guide rail to support the crosshead pin and to transfer the side thrust of the crosshead to the engine frame. In some old MAN B&W engines and SULZER RND engines, the piston rod passes through a bore in the crosshead and is bolted from the bottom by means of fine threaded nut. In the new design engines such as MAN SMC/ ME and SULZER RTA/ RT flex, the pison rod palm rests on the crosshead flat surface and four hydraulic bolts are used to tie them together. Guide and guide shoe, along with the connecting rod and crosshead, is an important arrangement as the guide directs the guide shoe in reciprocating direction while absorbing the side thrust produced during the motion of the connecting rod. The guide comprises of guide rail (normally integrated/ bolted with the frame) and guide plates, in which, the guide shoe moves up and do...
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Removing and replacing a broken tie rod

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The  tie rods on a 2 stroke marine diesel engine hold the components of the engine together in compression and transmit the firing loads to the bedplate. Breakage, usually due to a fatigue fracture, can be caused by incorrect tightening, misalignment between the mating surfaces, overloading of the engine etc. Sods law dictates that often the bolt will fail at mid length. The top half can be removed by lifting it out, however the removing the bottom half will present a challenge, due to the restriction in headroom in the crankpit. Broken tie bolt (above) and right, detail of fatigue fracture. The most obvious method of removal may seem to be to cut the tierod out in small pieces using a grinding wheel/ burning gear. This is not recommended. Two alternatives are available: The first involves passing a wire loop down the tierod tube to the bottom of the tiebolt and lifting the bolt out. The second method outlined below involves jacking the bolt out from b...
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All about safety valve

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SAFETY VALVES At least two safety valves have to be fitted to the boiler. They may be both mounted on a common manifold with a single connection to the boiler. The safety valve size must not be less than 38mm in diameter and the area of the valve can be calculated from the following formula C x A x P = 9.81 x H x E where H= Total heating surface in m3 E = Evaporative rate in Kg steam per m2 of heating surface per hour P = Working pressure of safety valves in MN/m2 absolute A = Aggregate area through the seating of the valves in mm2 C = the discharge coefficient whose value depends upon the type of valve. C=4.8 for ordinary spring loaded valves C=7.2 for high lift spring loaded valves C= 9.6 for improved high lift spring loaded valves C= 19.2 for full lift safety valves C= 30 for full bore relay operated safety valves LIFT PRESSURE The safety v/v must be set at a pressure not exceeding 3% of the approved boiler working pressure. It is normal to set the suphtr saf...
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