120B E120B 087-0308 AP12 Hydraulic Main Pump Assembly Compatible with CAT

1. Product Overview & Wholesale Price Advantage

The CAT 120B / E120B AP12 Hydraulic Main Pump Assembly (OEM Part # 087-0308 / AP12) is a high-pressure dual axial piston variable displacement pump engineered for 12-ton medium excavators operating under continuous trenching and earthmoving works.

• Direct Factory Wholesale Price: $1,650 – $2,950 USD (Direct Source Supply — Save 50%–65% vs Regional OEM Dealer Markups)
• Zero Middleman Markup: Shipped straight from our manufacturing floor with zero distributor extra fees
• MOQ & Bulk Tier Discount: 1 Unit (Tiered volume wholesale discounts available for international equipment fleets & repair dealers)
• Lead Time: 1–3 business days (Large factory stock ready for immediate air/sea shipping)
• Quality Guarantee: 12 Months full replacement factory warranty with 100% dynamic 350 Bar bench test video proof

2. Application Worksite Checklist (施工场景清单)

Precision-matched flow control designed to deliver smooth hydraulic power under continuous field operations:

• Urban Utility Trenching & Canal Excavation: Fine hydraulic metering for smooth boom and arm excavation with CAT 120B excavators.
• Agricultural Land Clearing: Sustained hydraulic working pressure under 350 Bar for rapid bucket loading cycles on E120B machines.
• Road Infrastructure Work: Thermal-resistant seal groups prevent internal oil bypass during long continuous operating hours.
• Demolition Operations: Heavy cast iron pump housing built to absorb continuous high hydraulic pressure shockwaves from breaker attachments.

3. Hydraulic Main Pump Troubleshooting & Diagnostic Guide (液压泵常见故障排查)

If your CAT 120B excavator is exhibiting hydraulic system power loss, consult the diagnostic guide below:

• Fault 1: Cold Machine Operates Normally, But Machine Slows Down & Drops Pressure After 1 Hour (冷车正常,热车掉压发慢)
  Root Cause: Thermal expansion wear gap between the piston shoes, cylinder block, and valve plate inside the AP12 rotary group.
  Solution: Replace with a complete drop-in CAT 120B main pump assembly (OEM 087-0308) or overhaul internal rotary group kit.
• Fault 2: Engine Stalls or Overloads When Actuating Hydraulic Boom/Arm (憋车/发动机过载熄火)
  Root Cause: AP12 pump regulator power-control spool jammed or hydraulic pilot regulator valve miscalibrated.
  Solution: Recalibrate pump regulator pilot pressure or replace the complete regulator valve assembly.
• Fault 3: Hydraulic Oil Leakage From Main Drive Shaft Seal Area (主驱动轴封高压串油漏油)
  Root Cause: Clogged casing drain line causing excessive internal pump housing backpressure, blowing out the front drive shaft seal.
  Solution: Flush housing drain lines, replace front drive shaft seal, and check pilot pump pressure.
• Fault 4: Abnormal Cavitation Noise or Severe Vibration From Main Pump (泵体异响抖动/气蚀)
  Root Cause: Air suction at inlet pipe, contaminated hydraulic tank filter, or worn drive shaft roller bearings.
  Solution: Replace suction line seals, flush hydraulic fluid tank, and replace drive shaft roller bearings.
• Fault 5: Black Metallic Filings Found Inside Hydraulic Tank Filter (油箱内有黑粉或金属屑)
  Root Cause: Severe friction galling on swashplate shoe bronze layer or cylinder block face failure.
  Solution: Flush entire hydraulic piping system, clean main control valve, and install a new CAT 120B main pump assembly.

4. Hot Machinery Replacement Parts Recommendation (5大品类热门推荐表)

Explore our factory-direct replacement hydraulic components compatible with major global excavator brands:

5. Frequently Asked Questions & Technical Support (QA 问答专区)

Q1: How do I verify if this AP12 main pump fits my CAT 120B or E120B excavator?
A: Check your original pump nameplate for OEM part numbers 087-0308 or AP12 stamp. You can also send us your machine serial number for instant fitment verification.

Q2: My CAT 120B excavator slows down after 1 hour of digging. Will replacing the pump solve this?
A: Yes, thermal slowdown is caused by internal pressure leakage inside the worn pump cylinder block. Installing our new AP12 main pump restores full hydraulic speed and digging power.

Q3: Is this CAT 120B hydraulic main pump bench tested before shipment?
A: Yes, every single pump undergoes a 5-step factory bench pressure test up to 350 Bar and volumetric efficiency check above 95%. A live test video is provided before shipping.