mechanical engineering

What is cavitation? Cavitation begins as the formation of vapor bubbles at the impeller eye due to low pressure. The bubbles form at the position of lowest pressure at the pump inlet (see Figure 1) which is just prior to the fluid being acted upon by the impeller vanes and then rapidly compressed. The compression of the vapor bubbles produces a small shock wave that impacts the impeller surface and pits away at the metal creating over time large eroded areas and subsequent failure. The sound of cavitation is very characteristic and resembles the sound of gravel in a concrete mixer. Figure 1 Pressure profile at the pump entrance. As you can see from Figure 1 the pressure available at the pump inlet which is the pressure that we would measure if we put a gauge at that point, can be reasonably high but still drop considerably as it makes it way into the pump. The pressure may be lowered enough that the fluid will vaporize and will then produce cavitation. The same effect can sometimes be ...

Introduction Mechanical seals are being used increasingly on fluid pumps to replace packed glands and lip seals. Pumps with mechanical seals perform more efficiently and generally perform more reliably for extended periods of time Mechanical seals are provided to prevent pumped fluids from leaking out along the drive shafts. The controlled leakage path is between two flat surfaces associated with the rotating shaft and the housing respectively. The leakage path gap varies as the faces are subject to varying external loads which tend the move the faces relative to each other. The mechanical seal requires a different shaft housing design arrangement compared to that for the other type of seals because the seal is a more complicated arrangement and the mechanical seal does not provide any support to the shaft. In order for the mechanical seal to perform over an extended time period with low frictional the faces are generally hydrodynamically lubricated. The fluid film will need to carry s...

ENGINE TURNING TOOL The top bolt in the cover plate of the bore for the engine turning tool is the timing bolt. The timing bolt is used to find the location of No. 1 piston on top center (TC). This is important to the serviceman because thereference point for all timing proce dures is with No. 1 piston put at top center on the compression stroke. The pipe plug (arrow) is removed from the flywheel housing to install the timing bolt. The optional engine turning tool fits in the bore in the flywheel housing and has teeth which engage with the flywheel gear teeth. The engine turning tool is a special tool used for rotation of the crankshaft of the engine when you need to make adjustments, time the engine, or turn an engine in storage. A 1/2 inch drive ratchet is used to turn the tool and the engine crankshaft. LOCATING TOP CENTER COMPRESSION STROKE FOR NO. 1 PISTON To find top center compression stroke for No. 1 piston, first turn the flywheel clockwise a minimum of 30 degrees. The re...

DIRECT INJECTION UNIT INJECTOR FUEL SYSTEM The 3500 Series Engines use the direct injection combustion system. This system has the advantages of: low heat rejection (in comparison to precombustion); low fuel consumption; and easy starting. UNIT INJECTOR AND CONTROL LINKAGE A fuel injector (7) is in a central bore of each cylinder head. The position of the rack (6) of each injector is changed by a bellcrank and bracket (5) that is held to the top of the cylinder head by bolts. Each bellcrank is moved by a control rod (4) connected to a hollow torsion shaft (1) through a lever (3). Rotation of the torsion shaft (1) is done by the governor input shaft (10) and causes in and our movement of the rack (6). The torsion shafts (1 and 8) are just below the camshafts of each bank of cylinders. A hollow cross shaft (9) at the front of the engine connects the right torsion shaft (1) and left torsion shaft (8) so they move together at the same time. The control rods (4) have a “click” screw adjustm...

FUEL SYSTEM The fuel transfer pump (2) pulls fuel from the tank through the inlet line (1) and forces it through a check valve and into the line to the fuel filters (3). After the fuel filters, the fuel flows to the fuel manifolds (6) along the inside of each cylinder bank. The top inlet passage of the manifold sends fuel through lines connected to each cylinder head. (Early engines had fuel filter screens in the connectors.) Fuel flows into a circular space around the injector (5). Part of this fuel is used for injection and part to cool the injector. (Later engines have fuel filter screens in the injectors.) The extra fuel that cools the injector is returned through lines to the bottom outlet passage of the fuel manifolds, through a pressure regulating valve (7) and then through a return line and to the tank. The priming pump (4) has a supply line from the inlet side of the pump and sends fuel through the filters, into the fuel manifolds. The location of the pressure regulating valve...