20/912800 JCB Parker Hydraulic Gear Pump 36/26cc

Product Overview

The 20/912800 is a JCB main hydraulic pump reference used on 3CX and 4CX backhoe loaders and is publicly cross-referenced with Parker hydraulic gear-pump configurations. The most commonly documented configuration is a 36 + 26 cm³/rev tandem gear pump based on the Parker PGP620 platform.

Parker’s official PGP/PGM 600 documentation classifies the PGP620 as a heavy-duty cast-iron external gear pump platform. The series supports multiple-section pumps, common or separate inlet configurations, high-power through-drive capability and continuous operating pressures up to 275 bar, depending on displacement and configuration. Parker also specifies a pressure-balanced thrust plate design for high efficiency.

Public Parker/JCB application information for the 20/912800 configuration identifies:

• 36 cm³/rev front pump
• 26 cm³/rev rear pump
• Counterclockwise rotation viewed from the shaft end
• 1-inch parallel keyed shaft
• SAE B 2-bolt mounting flange
• Common 2-inch SAE split-flange inlet
• 1-1/16″-12 UNF front outlet
• 7/8″-14 UNF rear outlet

Because multiple historical Parker/JCB cross-reference numbers exist, including 7029122001 and 7029122091, the exact replacement should be confirmed from the original nameplate and physical interfaces rather than from the JCB number alone.

Our replacement unit is manufactured around the original tandem-pump architecture and undergoes 100% simulated operating-condition testing to verify dual-section flow, pressure, leakage, rotation and running stability.

Technical Specifications

20/912800 / 7029122091

• JCB Part Number: 20/912800
• Parker/JCB Cross Reference: 7029122091
• Pump Type: Tandem External Gear Pump
• Parker Platform: PGP620
• Product Family: PGP/PGM 600 Series
• Configuration: Twin / Tandem Gear Pump
• Front Displacement: 36 cm³/rev
• Rear Displacement: 26 cm³/rev
• Rotation: Counterclockwise, viewed from shaft end
• Drive Shaft: 1-inch parallel keyed shaft
• Mounting Flange: SAE B, 2-bolt
• Common Inlet: 2-inch SAE split flange
• Front Outlet: 1-1/16″-12 UNF
• Rear Outlet: 7/8″-14 UNF
• Front Pressure: 275 bar in published Parker/JCB application data; a historical Parker engineering drawing lists approximately 255 bar for the 36 cc section
• Rear Pressure: 275 bar
• Typical Speed Range: 500–2600 rpm in the historical 36/26 Parker engineering drawing
• Control: Fixed Displacement
• Housing: Heavy-Duty Cast Iron
• Thrust Compensation: Pressure-Balanced Thrust Plate
• Weight: Approximately 26 kg according to public 36/26 Parker/JCB application data; actual assembly weight varies with shaft, porting and mounting configuration

Parker’s official manual states that the weight of a tandem PGP620 pump is the sum of the individual pump sections and varies according to porting, shaft and mounting configuration.

Related 20/912800 Cross References

Public documentation associates 20/912800 with several JCB/Parker references, including:

• 20/912800
• 20/903100
• 20/902900
• 400/E0868
• 7029122001

However, 7029122001 and 7029122091 should not automatically be treated as identical complete configurations. Parker PGP620 uses a detailed ordering structure in which displacement, shaft, flange, ports, rotation and multi-section configuration are separately defined.

Key Technical Advantages

1. 36 + 26 cm³/rev Tandem Configuration

The most important characteristic of the 20/912800 is its 36 + 26 cm³/rev dual-pump configuration.

Combined geometric displacement:

36 + 26 = 62 cm³/rev

At 1000 rpm, the theoretical combined displacement flow is approximately:

62 L/min

This is a geometric calculation only. Actual flow depends on volumetric efficiency, pressure, oil temperature, internal leakage and pump condition.

2. Heavy-Duty Cast-Iron PGP620 Platform

Parker’s official catalog identifies PGP620 as a heavy-duty cast-iron pump and lists construction, material handling, agricultural, forestry and industrial applications.

The cast-iron housing is appropriate for demanding mobile hydraulic environments with significant pressure and mechanical loading.

3. Pressure-Balanced Thrust Plate

Parker explicitly lists a pressure-balanced thrust plate design for high efficiency in the PGP620 platform.

In a positive-displacement gear pump, hydraulic loading creates axial forces that affect end clearance and leakage. Pressure-balanced thrust-plate architecture is intended to manage those loads and support efficient operation.

4. Modular Tandem Architecture

The official PGP620 platform supports:

• Multiple sections
• Common inlet configurations
• Separate inlet configurations
• High-power through-drive capability

The 20/912800 should therefore be considered an engineered tandem assembly rather than two unrelated gear pumps joined together.

5. High-Pressure Mobile Hydraulics

Parker specifies continuous PGP620 operating pressures up to 275 bar / 4000 psi, subject to displacement and configuration.

This makes the platform well suited to demanding JCB backhoe-loader hydraulic systems.

6. Simplified Power Transmission

A tandem pump allows two hydraulic sections to share one mechanical input. This provides multiple independent hydraulic flow paths from a single engine/PTO-driven assembly, which is particularly useful in mobile construction machinery.

7. Standardized SAE Interfaces

Public 20/912800 data identifies an SAE B two-bolt mounting flange, while Parker’s PGP620 platform supports SAE mounting and SAE split-flange/straight-thread port options.

Application Areas

JCB 3CX Backhoe Loaders

The strongest documented application for 20/912800 is the JCB 3CX family.

Published application references include:

• JCB 3CX
• 3CX PC
• 3CXSM
• 3CX Contractor
• 3CX444 Super
• Various sideshift and engine configurations

JCB 4CX Backhoe Loaders

The same public application sources also associate the pump with:

• JCB 4CX
• 4CX444
• 4CX444 Super
• 4CXSM444
• 4CXSM444 Super

Other Mobile Hydraulic Equipment

The wider Parker PGP620 platform is also used in:

• Construction equipment
• Material-handling equipment
• Agricultural machinery
• Forestry machinery
• Industrial hydraulic equipment

Expert Maintenance Tips

Treat It as a Tandem Pump

The critical hydraulic configuration is:

36 + 26 cm³/rev

Checking only one section can result in partial hydraulic-system performance after replacement.

Keep the Two Outlet Circuits Correct

The documented configuration uses:

• Front outlet: 1-1/16″-12 UNF
• Rear outlet: 7/8″-14 UNF

Ensure each hydraulic line is connected to the correct pump section.

Verify Counterclockwise Rotation

The published application configuration is:

Counterclockwise when viewed from the shaft end

The engine/PTO drive direction must therefore be verified before installation.

Inspect the Drive Shaft

The published configuration uses a:

1-inch parallel keyed shaft

Inspect:

• Shaft diameter
• Key condition
• Coupling engagement
• Shaft alignment
• PTO-drive condition

Excessive shaft loading can accelerate internal gear and bearing-support wear.

Control Suction-Line Velocity

Parker’s official PGP620 manual specifies a maximum pump inlet flow velocity of 3.0 m/s, while pump outlet and specified motor-port flow velocities should not exceed 6.1 m/s.

Therefore, replacement selection should consider suction-line diameter and actual flow, not only fitting thread size.

Maintain Hydraulic Cleanliness

Parker’s PGP620 guidelines recommend increasing filtration performance as operating pressure rises:

• 140 bar: ISO 4406 20/18/15
• 210 bar: ISO 4406 19/17/14
• 275 bar: ISO 4406 17/15/12

When replacing a pump on an older JCB 3CX/4CX, inspect the reservoir, suction screen and return filter at the same time.

Avoid High-Load Cold Starts

Parker specifies a normal operating-temperature range of -15°C to +80°C for PGP620. Cold starts between -20°C and -15°C are limited to ≤1500 rpm, and allowable pressure depends on fluid temperature.