Экскаваторын үндсэн гидравлик насос: эвдрэлийн шинж тэмдэг ба солих насосыг хэрхэн тааруулах

The Main Pump Is the Most Expensive Wrong Order on the Machine

On a 20-ton excavator the main hydraulic pump typically accounts for 30 to 40 percent of the total value of the hydraulic components. It sits behind the engine flywheel housing, driven through a spline or a coupling, and in a tandem arrangement two pump bodies share a single input shaft. That shared shaft is why one worn piston group distorts the pressure and flow of the whole unit, and it is why the usual reaction is to replace the entire pump.

That reaction is also the most expensive one. More than half of the pumps sent to us for assessment were not worn out at all. They had a regulator problem, a solenoid problem, or a pilot circuit problem. Separate those three from a genuinely worn pump body before any money is spent.

Four Symptom Groups, Four Different Causes

• Every function slow, pressure gauge reading low: check pilot pressure and the main relief valve first. Low pilot pressure keeps the main valve from opening fully, and the machine behaves exactly like a worn pump.
• One function slow, the rest normal: the fault is almost always in that circuit's spool or in the cylinder's internal leakage. In a tandem pump each body feeds one group of functions, so swapping the pilot hoses is a quick way to prove which side is involved.
• Hydraulic oil heats up fast and turns dark: the classic signature of wear on the piston group and valve plate. Hot oil thins further, which accelerates the wear, so the problem compounds itself.
• Noise from the pump body, copper flakes in the return filter: at this point internal wear is confirmed. Continuing to run it contaminates the entire system, travel motors and swing motor included.

One detail matters here: read the colour of the debris. Copper-coloured particles usually come from the valve plate or the slippers, while ferrous particles point to bearings or gears. Getting the colour wrong sends the repair in the wrong direction.

Read the Plate Before You Talk About a Model

Ordering by machine model is the single most common cause of a wrong pump. Two CAT 320D machines from different years or serial ranges can carry different pump batches, and the PC200-7 and PC200-8 pumps are not interchangeable at all. The reliable method is a photo of the plate on the side of the pump body, which normally carries the brand, the series code, the displacement, the rotation direction and the serial number.

• CAT 320D class machines commonly use SBS-series tandem pumps, with front and rear displacements marked separately on the plate.
• Komatsu PC200 series commonly use the HPV series. The exact code varies by model and generation and has to be read from the plate.
• Hitachi ZX200 series also use HPV-series pumps. The codes look close to the Komatsu ones but the units are not interchangeable, so never carry a number across brands.
• Kawasaki K3V and Rexroth A8V series appear widely on Chinese-built and some Korean machines.

Displacement on the plate is normally given in cc/rev, with two figures for the front and rear bodies. Those two numbers are the most direct way to confirm the tandem specification.

Regulator Faults: The Most Commonly Misdiagnosed Failure

The regulator converts pilot pressure into a change of swash plate angle. When it fails, the mechanical parts of the pump are still sound but the output flow is no longer controlled. The machine becomes slow, the engine labours, or pressure reads normal at no load and collapses under load.

The test is simple. Swap the two pilot hoses at the regulator. If the fault moves with the hoses, the problem is on the pilot side. If it stays where it was, the problem is in the regulator itself or inside the pump. That one step can save the price of a complete pump.

Solenoid valves behave the same way. A proportional solenoid with drifted coil resistance, or a connector with water ingress and green corrosion, will hold the pump at minimum displacement. Measure the resistance and inspect the connector before removing the pump.

Rebuild, New, or Remanufactured

• Seals aged, regulator failed: a seal and regulator kit is enough, and it is the cheapest option by far.
• Piston group and valve plate lightly worn, pump body not scored: a full rebuild with a lapped valve plate and a new piston group usually lands at 40 to 60 percent of a new pump.
• Pump body scored, bearing seats worn: a rebuild rarely pays. Fit a new pump.
• Used pumps: only worth considering with an original pressure test report. Without one the risk outweighs the saving.

The decision on a rebuild rests on the scoring depth inside the pump body, which can only be judged on the disassembled unit. Any conclusion drawn from photographs alone is unreliable.

Five Numbers to Send Before Ordering

1. Machine model and serial number
2. A clear photo of the pump plate showing brand, series code, displacement and serial
3. Front and rear displacement figures
4. Rotation direction, viewed from the input end
5. A description of the fault, including pressure readings, oil temperature and any noise

How Smile Machinery Handles It

Once the plate photo arrives we check three things before quoting: whether the tandem specification matches the machine, which regulator and solenoid interface the unit uses, and whether the coupling should be replaced at the same time. The quotation follows that check, not the other way round.

Pumps shipped to Russia, Kazakhstan and Uzbekistan travel with their pressure test record and fitting notes. Rebuilt units are labelled as remanufactured and are never sold as new.

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