4 stroke Crank

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Crankcase relief valve testing

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FLAME ARRESTORS AND SHIELDING The intention of the requirement to shield the valve discharge was to reduce the possible danger to personnel from flame emission. However explosion testing has shown that whilst a flame arrestor will work satisfactorily when shielding is not fitted, when shielding is fitted, the energy from the discharge is focussed in one direction, and there will be an emission of flames during an explosion. The fitting of shielding also reduces the effective outflow area of a valve. Since July 2002 it has been a Lloyds Register rule requirement to fit flame arrestors and to test the relief valve with any proposed shielding to be fitted to the valve when installed on the engine. A test procedure for new crankcase relief valves has been developed over the past four years by MAN B&W, The Physical Test Institute in the Czech Republic , Hoerbiger, and various classification socie...
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Crosshead

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The Crosshead The crosshead pin connects the piston rod to the connecting rod. On either side of the crosshead pin are mounted the crosshead slippers. The slippers run up and down in the crosshead guides as the piston and rod are reciprocating and prevent the top of the connecting rod from moving sideways. The crosshead pin sits in the crosshead bearing which is either a forked type (shown left), where the bearing housings are mounted on the top of the connecting rod either side of the piston rod, or of the continuous type (shown above and below), where the bearing housing is formed by the top of the connecting rod. On the forked type, the piston rod passes through a hole in the crosshead pin and is secured by a nut. On the continuous type, the piston rod has a foot which is bolted onto the top of the crosshead pin. Modern engines are fitted with the continuous type of bearing. The crosshead bearing is difficult to lubricate effectively. Because the top of the connecting rod s...
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Fuel Pump

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Medium speed four stroke engines are equipped with jerk type fuel pumps, one for each cylinder. A plunger operated by a cam reciprocates in a barrel. The plunger has a helix machined into it which also forms a vertical groove and an annular groove at the base of the helix. The barrel is located in the pump body which has spill ports, connected to the suction side of the pump, drilled so that they are above the top of the plunger when the cam is on the base circle. The plunger is keyed to a sleeve which has a gearwheel (pinion) machined into it. The pinion meshes with a rack which can rotate the plunger relative to the barrel. The rack is connected to the engine governor. As the plunger moves upwards in the barrel, injection will commence once the plunger has closed off the spill ports and the pressure builds up. As soon as the helix or scroll passes the spill ports the pressure above the plunger will immediately drop, even though the...
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