Locomotive Protective Devices PDF
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This document discusses protective devices for locomotives, focusing on those that safeguard mechanical and electrical systems against various issues such as low water, crankcase pressure, hot oil, low oil, and engine overspeed. It details the operation and testing of these systems.
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J e G c c G c c G C G c c c c; CL c CHAPTER Protective Devices G G C G Introducti...
J e G c c G c c G C G c c c c; CL c CHAPTER Protective Devices G G C G Introduction G c There are many devices and systems on the locomotive designed to protect the locomotives mechanical and electrical systems. In this section we will focus on the G main protective devices that protect the engine against; c Low water, G Crankcase Pressure HotOil G LowOi1,and G Engine Overspeed G c - EPD ENGINE PROTECTION DEVICE e Low Water & Crankcase Pressure Protection - “ I x G A low water detecting portion of the EPD,(Figure 9. l), balances water pressure G against airbox pressure. When water pressure falls, the device dumps oil from the governor supply line, causing an engine shutdown. e b c c - ITS Locomotive Training Series Student Text 9-1 a 0 3 While there is no air box pressure when an engine is shut down, there is spring pressure. This spring pressure must be acted against by water pressure in order to keep the device latched in. On certain devices the static water pressure working against spring pressure will not keep the device latched in when the engine is shut down. This is not necessarily an indication that the device is defective. It is merely necessary to reset the device immediately after engine start. Figure 9.1 EPD Testing EPD Operation Operation of the low water shutdown device, Fig.9.2, should be checked at the 4d intervals stated in the Scheduled Maintenance Program or whenever faulty operation is suspected. d 13) To test operation of the low water detecting device, run the engine at idle speed and turn the test cock mounted on the water pump discharge elbow to the horizontal 3 position. The low water button should pop out smoothly without hesitation after water trapped behind he operating diaphragm escapes through the drain hole provided (in not 44 mom than a fa0 seconds oftime). Return the test cock to the vertical position. d 3 Figure 9.2 Test Cock Operation iJ 9-2 Eiectro-MotiveModel 567.645 & 710 Series Diesel Engines L) c c: - -.. c/ c( c Observe the low oil plunger on the governor as it moves out. The plunger should c extend fully and the engine begin to shut down in about 5 5 seconds. As the engine be- gins to shut down reset the low water button and the low oil plunger. Operate the rack c positioning lever to bring the engine back up to idle speed before complete shutdown. Verify that the low water button stays set. c If the low water shutdown reset pushbutton does not pop out freely without c assistance when the test cock is opened and the engine is at idle. the device should be c removed and replaced with an operative device. Refer to the Service Data page for a listing of instructions covering maintenance and qualification of the low water protector. L Special apparatus is required for proper testing. c The crankcase pressure detector may be tested in a similar manner by applying a rubber tube over the test opening on top of the detector and applying suction to trip the c upper button. c The combination low water and crankcase pressure detector is a mechanically c operated, pressure-sensitive device designed to determine abnormal conditions of engine coolant and crankcase pressures. c c The low water safety device is a spring loaded, normally open, two-way valve piloted by a latching mechanism on a diaphragm stack. There are two diaphragms in the stack; c one sensing water pressure into the engine, and the other sensing engine air box pressure. c c -NOTE: The air box-to water diaphragm area ratio for TURBOCHARGED IS 1 :l. G The air box-to water diaphragm area ratio for BLOWER (ROOTS)IS 3:l. G Under normal operating conditions water pressure exceeds air box pressure. (5, The low water reset button WILL TRIP when water pressure IS within 1/2 psi of air box pressure. The following conditions will cause the detecor to trip: c Loss of water level. c Pump cavitation due to air entrainment (during sxrting). c, Pump cavitation due to water temperature apprcaching boiling c/ point. Applicable to non-pressurized systems. G Excessive air box pressure due to turbine surging at low throttle speeds. (Turbochargedengines only.) G OVERFILLING the water tank can cause low waTer shutdown. cj c 5, G G c ITS LocomotiveTraining Series -Student Text c/ c 3. Air Box Pressure 4. Oil In From Governor 5. Trip Position 6. Latch Position 7. Oil Return To Crankcase 8. Vent Fitting 9. Crankcase Pressure Negative Figure 9.3 Low Water Pressure Condition In some installations, the test cock is locateu at the bottom of the device while, in others, it is in the water pump outlet elbow. By rotating the test cock handle as illustrated in Figure 9.2, to the horizontal position, the discharge of water from the small orifice hole in the cock should be a steady flow. Because of contaminants in the cooling water, the small orifice in the cock may become plugged, reducing or restricting the bleed off of water pressure on the water diaphragm. In most cases, rapidly opening and closing the test cock a few times will dislodge the obstruction and allow the low water detector to trip. Plugging of the test cock in no way affects the operation of the low water device. With the engine running at idle speed, placing the test cock in the horizontal position, and obtaining a free flow of water from the orifice, should trip the device on the first or second try. If the device does not trip, the device should be taken off and checked on a test panel to determine the cause of malfunction. It is recommended that.”* the operation of the lo ector be checked monthly...I ”’4.X *CI rb( “ 19s ElectroMotive Model 567.645 & 710 Series Diesel Engines G i c G c c c G G (d. c c c 1. Water Pump Discharge Pressure 2. Water Pump Inlet Pressure c ~~~~ U ' 3. Alr Box Pressure 4. Oil In From Governor c ! , 5. Latch Position 6. Trip Position c 4 7. Oil Return To Crankcase 8. Vent Fitting 9. Crankcase Pressure c Positive c Figure 9.4 Positive Crankcase Pressure Condition c Crankcase Pressure Detector (EMDEC) c c, The crankcase pressure detector used on EMDEC equipped engines senses any malfunction which causes a positive, rather than the normally negative engine di crankcase pressure. When the device senses a positive crankcase pressure, it trips a switch to signal the EMDEC master Electronic Control Module (ECM) which shuts c the engine down. c The EMDEC switch type crankcase pressure detector has a long stem held in a latched position until a positive pressure builds up in the crankcase. This pressure CI pushes on the large diaphragm which, in moving, releases the long stem. c Outward movement of the stem operates a lever to close contacts in a switch mechanism attached to the bottom of the detector. This switch provides the shutdown G signal to the ECM. c: Negative pressure is normally maintained by the crankcase ventilating equipment. The following are sonqiitions (upgly to troth EMDEC and mechanical G injector systems) that can cause a crankcase pressure detector to trip: c Blocked oil separator or aspirator tube in the exhaust, excessive oil level in c crankcase, resulting in blockage of oil separator. 40 Cylinder compression leak into the oil pan or top deck from a cracked cylinder head, cracked piston, loose injector, improperly installed or G broken rings, broken valves or badly worn valve guides. c I c ITS Locomotive Training Series - Student Text 9-5a C J i Pressurized air from the air box leaking to the crankcase from hardened or broken liner seals, broken crab bolts, loose crab bolt retainers or extreme cylinder scoring. Overheated part in crankcase igniting oil vapours (crankcase explosion). Incorrectly installed lube oil pressure relief valve, allowing oil splash to reach the diaphragm of the detector. -WARNING: Following an engine shutdown caused by the tripping of a conventional or EMDEC crankcase pressure detector, DO NOT open any handhole or top deck covers to make an inspection until the engine has been stopped and allowed to cool for at least 2 hours. DO NOT attempt to restart the engine until the cause of trip has been determined. The action of the pressure detector indicates the possibility of a condition within the engine, such as an overheated bearing, that may ignite the oil vapours with an explosive force, if air is allowed to enter the engine. If the crankcase pressure detector cannot be reset, DO NOT operate the engine until the pressure detector has been replaced, since the diaphragm backup plates may be damaged. Figure 9.5 Crankcase Pressure Detector 1% Electro-MotiveModel 567,645 & 710 Series Diesel Engines c c c c c4 Hot Oil Detector c A thermostatic valve located on the outlet elbow from the main lube oil pump is c calibrated to open when lube oil temperature reaches nominally 260°F (126OC).At this temperature the probability exists that either the lube oil cooler is plugged on the water c side, or steam pressure in the cooling system is preventing engine shutdown by the low c water detector. G When oil temperature causes the valve to open, pressure in the line to the oil pressure sensing device in the engine governor is dumped. The device sees low oil c pressure and reacts to shut the engine down. c c c I 252-257 275 I c c c c c c c c G c Fig. 9.6 Hot Oil Detector Thermostatic Valve and Location (Right) c The thermostatic valve is non latching, and it will reset automatically when oil c temperature falls. The engine may then be restarted when the governor low oil plunger c is reset. G -WARNING: After it has been determined that hot oil is the cause for engine shutdown, make G no further engineroom inspections until the engine has cooled sufficiently to c preclude the possibility that hot oil vapor may ignite. When a low Oil shutdown occurs, always inspect for an adequate supply of water and oil before attempting LJ to restart the engine. Also check engine water temperature. Do not add cold water to an overheated engine. c 9 c c c ITS Locomotive Training Series -Student Text 9-7 a c L) L) 3 The hot oil detector should be removed from the engine and tested at intervals suggested in the applicable Scheduled Maintenance Program. Test the hot oil detector 3 as follows: 1k19 Connect a 50 psi (345 kPa) air line to the hot oil detector inlet port (port with arrow) 3 3 Attach a return line to the outlet port to prevent creating oil spray when detector opens. 3 Place detector in a 235" F ( 112.6'C) oil bath with a thermometer. 3 Check for leaks between the body and cap. 3 3 Increase the temperature of the oil bath to 258" F (12SoC),the valve should open. If not the detector should be replaced with a qualified unit, 3 On locomotives equipped with EMDEC fuel injection, the Hot Oil Detector has 3 been replaced with a Lube Oil Temperature sensor which reports the oil temperature to 3 the computer. 3 Low Lube Oil Shut Down r9 The low lube shutdown system protects the engine in case of a failure of the 3 mechanical support systems. 3 The shutdown system can be activated by: 61b 1. "True" low lubricating oil pressure; 3 2. "False" low lube pressure caused by a failure of the cooling system and 3 detected by either of the low cooling water portion of the E.P.D. or hot oil detector; 3 3. "False'' low lube pressure caused by the E.P.D. sensing a positive crankcase 3 pressure (crankcase is normally under a slight vacuum); 3 4. "False" low lube pressure caused by manual engagement of the system 3 connected to a lube oil line from the engine on one side and speed setting oil pressure on the other side. (9 Should oil pressure in the line drop below the speed setting oil pressure, the cs system will take action to shut down the engine. 3 When the engine is at idle, there is a mechanism that builds in a delay of 50 to 60 3 seconds. This delay is to allow oil pressure to build up when starting the engine. The delay is reduced in steps to the third throttle position. In the fourth position and 3 higher there is no time delay in the shut down system. ,Q.A Ls I 9 4 Electro-MotiveModel 567.645 & 710 Series Diesel Engines L) C c C c c To shut the engine down, the system bleeds c the speed setting oil from the top of the speed c LOW Oil Pressure setting piston. c Shutdown Plunger The governor reacts by moving the layshaft and racks to the no fuel position, shutting down c the engine. c A switch is tripped setting off an alarm in the operators cabin, and a plunger protrudes from the L side of the governor exposing a red band. c The engine cannot be restarted until this plunger is reset. e The hot oil detector and engine protective c device both simulate a loss of oil pressure by bleeding oil pressure off of the line to the governor. c c Figure 9.7 Low Oil Shutdown Button c c Engine Overspeed c c The engine overspeed trip is a mechanical safety device to G stop fuel injection if engine c speed exceeds specified limit. A flyweight mounted on G counterweight at front of right bank camshaft activates the trip. G ll centrifugal force exceeds adjustable spring tension, G flyweight moves out. c When the flyweight moves out, it contacts the trip pawl. LATCHED msinoN TRIPPED POSrnON c The Trip pawl uses an actuating Figure 9.8 Overspeed Trip spring to move connecting G links, which rotate a trip shaft on each bank of the engine. G The trip shafts extend along each top deck behind thecylinder heads. Under each G injector rocker arm,-there is a pawl in contact with a small cam on the trip shaft. C T ~pt*) :.w ( 1 G When the tri cam rotates upward, it raises a pawl under the rocker arm to prevent -p-f, further actuation o the el injector. c An external latch lever is located on the overspeed trip housing just above the G accessory drive housing. G Trip speed is usually set at 10% in excess of normal engine full speed; 900 rpm c units trip at 990 rpm. c - ITS Locomotive Training Series Student Text./ / wa c 3i Figure 9.7 Overspeed Trip I 16-71OG limit has been revised to 1035-1050 rpm to prevent tripping system during locomotive transition. Adjustment Determine trip speed using a hand tach applied to end of camshaft through access cover on RH front camshaft cover of trip housing. Run engine up until trip lever moves. NOTE If trip does not occur before 990 rpm (orotherwise specified maximum speed), do not exceed the 10% overspeed. The mechanism needs adjustment. Shut engine down and remove large cover from right side of housing. Back-off spring tension by loosening locknut, then adjusting nut. Note: Loosening spring tension decreases t i p speed. Secure nuts and restart engine. Again using hand tach, observe trip speed. Repeat as necessary to fall within specified range. Note: Always make adjustments in tightening direction. The minimum clearance between flyweight and pawl is.010". Is10 Electro-Motive Model 567,645 & 710 Series Diesel Engines G c;. ,..... ~. __ c - 1... G E G G G G G G 0 G c G G G 6 G c G G c G G c G G G c G e e I d c c c c..~. -~......... __.... G e c SYSTEM BLOCK DIAGRAM ic "EMDEC" 16 Cylinder c c G G c G c I INTERFACE1 II c 24 VDC c TRS G 3.1.). G I FEEDBACKS + ECM t SENDER -1c 0 INJECTORS P f i 0 G Tf- ECM RECEIVER G G C -. G P f i G C G C f - G c G G Figure 4.11 EMDEC System Bloc& Diugrurn c t s s c ,l. c SDBOMACStudentText 4-7 I 6 c c c C c G c G G c; G G e G c c c bua G c G 8 G e G e G G G G e c C c c G G c c........ --.... ~... G G c G C c c G G G Sensor Output (Volts) c 0 4 h) 0 P c11 m G e G G -...... -. -.. G ci c; G G G G G G c G G ci G G G G F 4 w c c 6