Identification Methods for Diesel Engine Plunger Couples

Plunger couples in diesel engines are vulnerable parts. Random replacement during diesel generator set maintenance leads to unnecessary waste, making it crucial to master their identification methods.

Overview of Plunger Pumps

Plunger pumps are categorized into radial and axial types based on plunger arrangement:

Axial plunger pumps: Plunger axes are parallel to the drive shaft.

Radial plunger pumps: Plunger axes are perpendicular to the drive shaft.

Both types share the same basic working principle.

Function of Plunger Couples

In diesel engine fuel injection pumps, plunger couples increase diesel pressure to meet injector requirements, control fuel quantity, and regulate supply timing. As critical components of the injection pump assembly, they require both excellent sealing and smooth sliding performance. Seizure or sticking of plungers can cause difficulty or failure in rack movement, leading to regulator malfunction.

Damage and Wear Patterns

The primary damage to plunger couples is wear, concentrated on localized working surfaces:

Plunger head and areas corresponding to the plunger sleeve's oil inlet hole.

Edge of the edge of the inclined chute supply stoppage (oblique groove cut-off edge) and oil return hole edge.

Inspection and Identification Methods

1. On-Vehicle Inspection

① Fault Analysis Method

Wear in plunger couples most significantly affects fuel supply advance angle. If symptoms include delayed start of fuel supply, premature end of supply, insufficient pressure, and absence of normal injection sounds when cranking the engine, plunger couples are severely worn and require replacement.

② Thumb Pressure Test

Remove the high-pressure fuel pipe, set the throttle to maximum fuel supply, and firmly press a thumb over the injector holder’s oil outlet. Crank the engine to activate fuel pump operation or use a screwdriver to press the pump foot. If the oil pressure is strong enough to resist thumb pressure, the plunger couples can continue in service; weak pressure indicates severe wear and the need for replacement.

2. Injector Testing Method

To inspect plunger couples for a specific cylinder:

Disconnect the high-pressure pipe and reconnect it at an angle to a standard injector (pressure adjusted to 19.6 MPa).

Position the injector nozzle downward, fix the throttle at maximum supply, and crank the engine with decompression engaged.

Observe fuel atomization: Good atomization indicates usable plunger couples; failure to inject fuel signals worn, ineffective plunger couples.

3. Instrument Measurement Method

Connect a pressure gauge (range: 0–60 MPa) to the cylinder’s injection pump high-pressure pipe.

Set the throttle to maximum supply, crank the engine to bleed air, and raise the gauge pressure to 24.5 MPa.

Monitor pressure decay: A drop from 24.5 MPa to 14.7 MPa should take no less than 5–10 minutes for the plunger couples to be considered in good condition.

4. Visual Inspection

Use the naked eye or a 4–10x magnifying glass to check for:

Obvious wear marks, linear grooves, or rust spots on plunger surfaces.

Blunting or chipping of edges on the plunger head’s oblique/straight grooves.

Plunger bending or head deformation.

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