carbon on the inside of the tip. Then they can be cleaned out by using the proper size spray tip cleaning wire.

Inspect injector parts for excessive wear, damage, defects, burrs, scratches, scoring, erosion, or chipping. Replace the damaged or excessively worn parts.

This manual covers the operating principles, disassembly, inspection, repair and assembly of the PT (type G) and PT (type R) fuel pumps. Testing and calibration are covered in separate manuals. Each part is disassembled, repaired and assembled in separate sections. This manual covers service and troubleshooting of the Cummins PT Fuel System used in older diesel engines such as the 855, L10, etc. It includes detailed specifications, illustrations and procedures to guide the mechanic with correctly repairing and overhauling the fuel system to the manufacturer’s specifications.

PT PACER cost-effectively integrates this primary benefit with the well-established Cummins hydromechanical PT fuel system. The product, developed by Cummins Engine Company, Inc., and its subsidiary Cummins. An important fuel injection system designed and manufactured by Cummins was the PT (pressure-time) injection system and first introduced in 1954 Obert 1968. This was Cummins’ primary fuel system.

Lap all of the sealing surfaces, such as the bottom of the injector body, the injector bushing, the valve seat, the valve cage, the check valve, and the spray tip, before you reinstall used valve parts in an injector.

Now you are ready to reassemble the injectors. Follow the steps prescribed by the manufacturer's maintenance and repair manuals. The injector is satisfactory if it passes these tests. Failure to pass any one of the tests indicates that defective or dirty parts have been assembled. In this case, disassemble, clean, inspect, reassemble, and test the injector again.

The Cummins Pressure Time (PT) Fuel Injection System (fig. 5-33) consists of the fuel pump (with governor), the supply lines, drain lines, fuel filters, fuel injectors, and shutdown valve. An aneroid valve is installed on the fuel system of turbocharged engines only.

As in previous sections of this chapter, we will cover troubleshooting, disassembly, inspection, reassembly, and testing of components. Remember, before performing any service on the PT injector or pump, refer to the manufacturer's maintenance and repair manuals.

Troubleshooting

Troubleshooting is an organized study of a problem and a planned method or procedure to investigate and correct the difficulty.

Most troubles are simple and easy to correct; for example, excessive fuel oil consumption is caused by leaking gaskets or connections. A complaint of a sticking injector plunger is usually corrected by repairing or replacing the faulty injector; however, something caused the plunger to stick. The cause maybe improper injector adjustment, or, more often, water in the fuel.

In general, the complaint of low pwer is hard to correct because it can have many causes. There are many variables in environmental operation and installations, and it is difficult to measure power in the field correctly. With the PT fuel system, you can often eliminate the pump as a source of trouble. Simply check to see that the manifold pressure is within specified limits. The fuel rate of the pump must not be increased to compensate

Figure 5-33.-Pressure-timed injection system.

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Cummins PT fuel pump is mainly divided into two types, one is PT (G) type fuel pump, 'G' means governor-controlled. It means that this type of pump is equipped with a mechanism - mechanical governor controlled by the centrifugal force of flying block.The other type is called PT (R) type. 'R' means Pressure-Regulated. Its outlet fuel pressure is regulated by a pressure regulating valve. The fuel is first adjusted by the gear pump through the pressure regulating valve. It uses a diverter valve to adjust the fuel pressure to the fuel injector, and the remaining fuel flows back to the gear pump inlet.

Both Cummins N and K series diesel engines use PT (G) fuel pumps.

Main features of Cummins PT pump fuel system:

In the PT pump fuel system, the fuel generates high pressure, and the timing distribution and fuel volume adjustment are in the fuel pump. In the fuel pump and fuel injector fuel system, the fuel generates high pressure, and the timing distribution and fuel volume adjustment are in the fuel pump and the injector, only about 20% of the fuel entering the injector is injected into the combustion chamber from the fuel injector, the remaining fuel cools and lubricates the injector and returns to the fuel tank.

Because the fuel pump in the PT fuel pump system only outputs low oil pressure without high-pressure fuel pipes, there is no problem of pressure waves at high speed, and the driving speed under the injector plunger is fast, the size of the injection hole is small, so the injection pressure can reach 100MPa, which is beneficial to combustion atomization, full combustion, and good economy. It can be seen that Cummins PT fuel system plays a vital role in the operation of Cummins diesel generator.

The test bench debugging method of Cummins PT fuel pump is as follows:

①Install the fuel pump on the test bench. After the fuel pump is connected to the drive plate, fill the pump housing and the oil inlet hole of the gear pump with clean test oil from the plug hole at the top of the fuel pump. Connect the oil inlet rubber hose and the cooling oil drain valve hose; check whether the voltage stabilizer is stable to ensure that the gear pump works stably; adjust the pointer of each measuring instrument to zero position.

Cummins Pt Fuel System Diagram

②Trial run. Close the idle small orifice valve, throttle valve and leakage valve on the test bench, and fully open the vacuum adjustment valve, oil cut off valve and flow adjustment valve. The throttle valve of the fuel pump is in the fully open position, and the double arm lever of the MVS governor is in contact with the high speed limit screw. Start the motor to make the fuel pump run at 500r / min.If the fuel pump does not suck oil, check whether the valve in the oil inlet line is open, whether there is air leakage, or the rotation direction of the fuel pump is reversed; test run for more than 5 minutes to allow air to be discharged from the oil and the oil temperature rises to 32~38℃.

③Check the tightness of the fuel pump. At a speed of 500r / min, close the vacuum adjustment valve while opening the flow adjustment valve, the vacuum meter reading should be 40kPa; apply a small amount of light grease to the vent hole at the main shaft sealing device of the front cove of the fuel pump, no inhalation means good seal; Check the tightness of the O seal ring of the throttle valve, the seal ring hole of the chronograph, the double arm lever shaft of the MVS governor and the adjusting screw, the gasket between the gear pump and the housing.If there are air bubbles in the fuel of the flowmeter, it means that air has entered the fuel pump in the above part.

④Adjust the vacuum. Fully open the flow adjustment valve on the test bench, the fuel pump runs at the rated speed of the diesel engine, and adjust the vacuum adjustment valve to make the vacuum meter reading 27kPa.

⑤Adjust the flow meter. The fuel pump runs at the nominal speed of the diesel engine, and the flow adjustment valve is used to adjust the float of the flow meter to the specified value.

⑥Adjust the speed of the disconnection point of the governor. The throttle valve is fully open, increase the speed of the fuel pump until the fuel pressure begins to drop, and check whether the speed of the fuel pump's disconnection point is within the specified value. If it is lower than the specified value, a gasket can be added between the adjusting spring and the snap ring; otherwise, the gasket should be removed. When the MVS governor is installed, it is adjusted with a high speed limiting screw.

⑦Check the fuel pressure point. Increase the fuel pump speed. When the fuel pressure drops to 276kPa, check whether the fuel pump speed is within the specified value range. Make the fuel pump continues to increase the speed, the fuel pressure should be able to reduce to zero, otherwise the fuel in the fuel pump is short-circuited.

⑧Commissioning of fuel outlet pressure at nominal speed and maximum torque point speed. Starting from zero fuel pressure, reduce the speed of the fuel pump to the calibrated speed and check whether the fuel outlet pressure meets the specified value. When the MVS speed governor is not installed, use the increase or decrease gasket to adjust. When the MVS governor is installed, use the throttle adjustment screw to adjust; when the fuel pump speed drops to the maximum torque point speed, check whether the fuel outlet pressure meets the specified value.

⑨ Adjustment of idle speed and fuel outlet pressure. Close the throttle valve, leakage valve and flow adjustment valve on the PT pump test bench, open the idle orifice valve, make the throttle valve shaft of the fuel pump in the idle position, make the fuel pump run at idle speed, and check whether the fuel outlet pressure meets the specified value. Adjustable with idle speed adjustment screw.

Hope the above methods help you debug the PT pump of Cummins diesel generator well.

Cummins Pt Fuel System Pressure

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