Details

Introduction
Rear Cover Hydraulic Test Rig (Electro-Hydraulic Functional Test Bench)
In any hydraulic assembly where the rear cover also governs valve behavior, tiny deviations don’t stay “tiny” for long. A few bar of pressure error, a sluggish response valve, an unnoticed free play band, or inconsistent drop/hunting behavior can turn into real field failures: unstable motion, slow or non-repeatable actuation, overheating, seal damage, premature wear, nuisance trips, or in the worst case—unsafe machine behavior under load. That’s exactly why this Rear Cover Test Rig exists. It is not just a pump-and-gauge setup; it’s a controlled, repeatable verification environment that forces the unit under test to demonstrate correct functional behavior across low-flow and high-flow conditions, pressure thresholds, timing windows, and stability checks—while recording the evidence digitally. By combining a high-pressure hydraulic supply, regulated flow control, calibrated measurement, model-wise test recipes, operator interlocks, and automated pass/fail reporting, the system closes the gap between “it seems to work” and “it is proven to work, every time, on every unit.”

Rear cover: what it is and where it is used
A rear cover is the end-cap / end-plate assembly bolted to the rear side of a hydraulic unit (typically a pump, motor, or a hydrostatic drive/transmission module). In many modern designs, it’s not just a protective cover—it is a functional hydraulic sub-assembly that contains precision oil passages and, often, integrated valve functions.

What a rear cover typically does
• Seals and closes the hydraulic housing, maintaining pressure integrity and preventing leakage.
• Forms internal oil galleries/passages that route pressure, return, charge, and drain flows correctly.
• Provides external interfaces (ports, test points, manifold connections, mounting features).
• Supports internal components (bearing seats, alignment features, thrust/end surfaces).
• Integrates control functions (depending on the design), such as:
  ▹ relief / pressure limiting functions
  ▹ response / modulation valves
  ▹ isolator / shut-off functions
  ▹ check / anti-cavitation functions
  ▹ damping features to prevent hunting/oscillation

When these functions are integrated into the rear cover, it becomes a performance-defining component: small deviations in machining, valve setting, or internal leakage paths can directly impact response time, stability, lift/lower timing, pressure regulation, and overall safety.

Where rear covers are used
Rear covers are widely used in:
• Hydraulic pumps (gear, vane, axial piston) — rear cover/end plate often carries porting and sealing surfaces; sometimes charge/relief functions.
• Hydraulic motors — rear cover can integrate port routing, check/relief behavior, and case drain paths.
• Hydrostatic transmissions (HST) / drive modules used in:
  ▹ tractors and harvesters
  ▹ skid steer loaders
  ▹ excavators and compact construction equipment
  ▹ industrial hydrostatic drives
• Mobile hydraulics valve-integrated housings, where OEMs combine multiple functions into one compact end cover to reduce external plumbing and improve packaging.

This is why rear cover testing is treated as functional validation, not just dimensional inspection—the test rig verifies how the rear cover behaves hydraulically under defined operating conditions.

1) What the machine does
Purpose
• Validates functional performance of rear cover models across defined flow conditions, pressure checks, timing checks, drop behavior (with response valve open/closed), and stability checks (hunting).
• Uses computerized measurement and control so dynamic pressure/flow/temperature/time can be displayed, recorded, and reported.
Models supported (as per the operator manual)

The rig is set up to test four different models, and the operator must choose the correct model because each model has different parameters.
Examples of model-wise functional coverage include:
• CRE 735XJ: Lift movement @ 5 LPM; response valve pressure; free play; drop (response valve open/close); hunting; lifting time; lowering time.
• CRE 735XJ (variant shown): Lift movement @ 16 LPM and @ 5 LPM plus the same core checks.
• XM 744 / XM 843: Lifting checks at higher and low flows (e.g., 24/7 LPM, 16/5 LPM), with the same core checks; XM 843 additionally includes lifting check when isolator valve is closed.

2) System architecture (how it’s built)
A) Main hydraulic system (UUT supply)
This is the primary power pack delivering controlled flow/pressure to the UUT.

Key hardware (from BOM):
• Reservoir: 500 L, MS fabricated.
• Main pump: Internal gear pump 46 LPM @ 2880 RPM, 250 bar (Rexroth AZPW series listed).
• Drive motor: 20 kW, 2880 RPM, driven by VFD.
• Pressure protection/control: Relief valve (0–250 bar), plus relief-cum-unloading valve set around 200 bar.
• Duplex high-pressure filtration: 10 μm and 5 μm duplex assemblies with bypass option and electrical + visual clogging indication.
• Instrumentation (primary):
  ▹ Pressure gauge (0–280 bar) with calibration certificate.
  ▹ Pressure transmitter 0–250 bar, 4–20 mA (Telemecanique listed).
  ▹ Flow meter 5–50 LPM with test certificate (Hydrotechnik UK listed) and stated as regulatable via VFD.

Oil care & tank hardware (from BOM):
• Level gauge + low/high level switches, suction strainers, drain valves, temperature gauge + RTD (4–20 mA).
• Heaters: 4 kW, 3-phase, 440 VAC (listed).

B) Cooling / temperature control loop
To keep oil temperature under control, the BOM shows a dedicated cooling circuit:
• Cooling line pump 40 LPM + motor + coupling; air radiator (STANHEX OC4-1 listed); low-pressure line filter with clogging indication.

C) Loading & clamping system (fixture actuation and controlled loading)
The rig includes a dedicated loading/clamping subsystem for consistent fixturing and controlled actuator behavior.
Loading/clamping components (from BOM):
• Loading gear pump 40 LPM, 210 bar.
• Actuators: double-acting cylinders (bore 70 mm, rod 45 mm, stroke 350 mm) with inbuilt LVDT + inbuilt pressure sensor.
• Inbuilt measurement in the loading actuator:
  ▹ Load sensing assembly 0–3000 kg (WIKA listed).
  ▹ Inbuilt LVDT assembly (stroke variant shown; model-specific stroke appears in BOM/manual).
• Hydraulic swing clamps (with overload protection), with clamping forces listed (e.g., 22.6 kN @ 200 bar and 13.9 kN @ 200 bar).
• Clamp filtration: 10 μm pressure line filter with bypass and electrical/visual clogging indicator.
• Directional control valves (example: Rexroth 4WE6 series) and modular flow control elements are listed for controlled motion.

D) Mechanical test bed & fixture foundation
• Dedicated casting bed / base frame and test bed for mounting the rear cover assembly, referenced to Neometrix drawings in the manual.

3) Measurement, control, and automation
Measurement philosophy
• The rig uses multiple pressure transmitters in ranges including 0–160 bar and 0–250 bar for dynamic indication and recording into the DAQ/control system.
• Filtration cleanliness is treated as a controlled condition: multiple filters with clogging indication are described, and clogging status is shown on the test screen.

Control panel & DAQ backbone
The manual describes the control panel and DAQ elements including:
• Emergency shutdown switch, DAQ/control system with touch monitors, PLC display of process parameters, keyboard/mouse, and UPS for controlled shutdown.

Hardware stack shown in the BOM includes:
• Siemens PLC / DAQ platform (IM151-8 PN DP CPU with I/O modules), WinCC flexible runtime (128 tags), customized software application, PC (dual core), touch monitor, UPS.

Signal wiring discipline
Wires are routed through cable trays, power and control wiring are separated, and junction boxes are used for power/control distribution.

4) Operator software experience (screens, interlocks, traceability)

Main screen structure (as described)
The main screen provides five operator paths:
1.  Test VTU (start test and select model)
2.  Maintenance mode (sensor calibration / edits; engineer-only use)
3.  Backup report (view test reports in Excel format for records)
4.  VTU test program edit (adjust parameters per model)
5.  Exit

Execute Test Window behavior (pass/fail visibility)
• On the model test screen, each step changes color: after completion the step turns “blue” when in range; if out of range it stays “red,” giving immediate visibility to failure points.

Calibration and system status screens
• Calibration windows are model-specific, allowing parameter changes per model selection.
• A system status screen shows the health of I/O: healthy signals remain green; unhealthy signals turn red.

Reporting features (DAQ/computer)
The manual explicitly lists that the computer/DAQ system supports:
• Test process display
• Online values for pressure/flow/temperature/time (and other parameters as applicable)
• Real-time charts/graphs
• Test result storage/retrieval
• Manual keyboard entry for test item details
• OK / NOT OK result generation

5) Test execution workflow (interlocked, guided procedure)
The operating procedure is designed around a guided “acknowledge” flow and defined lever positions:
1.  Start the program, enter details, select model, start system, clamp, and start cycle.
2.  Perform flow tests and checks by moving the PC lever to defined positions and pressing acknowledge at each defined step (examples include full PRM flow, idle RPM flow, and subsequent steps).
3.  Relief valve pressure test uses PC lever movement “ahead of stopper” then acknowledge.
4.  Drop tests (response valve open/close) are sequenced with acknowledge prompts, motor stops, and timer start actions.
5.  Free play test is executed by moving the PC lever just before stopper and further ahead with acknowledge at both points.
6.  Isolator valve check is triggered by moving PC lever up and acknowledging.
Interlock rule (critical): if acknowledge is not pressed at the defined positions, the test will not proceed further—tests are interlocked by design.

6) Safety design (hard interlocks + operational discipline)

High-pressure handling warning
The manual flags the system as high pressure and intended for trained personnel, with risk of injury if mishandled.
Motor–pump safety interlocks (automatic inhibit/shutdown)
The motor-pump unit will not start or will shut off if any of these occur:
• Low oil level
• Motor overload
• Input power supply phase disorder
• Any filter clogged condition (across filters)
• Emergency stop activation

Installation and operating do’s/don’ts (practical safety)
The manual includes explicit installation cautions:
• Motor rotation direction must match pump (clockwise viewed from back of motor)
• Ensure good coupling; use anti-vibration pads
• Fill clean hydraulic oil; keep suction valve open
• Increase pressure slowly; keep tank covered

And operational discipline:
• Don’t run motor with suction valve closed / low oil / contaminated oil; don’t run motor in anticlockwise direction; don’t interrupt while running.

7) Maintainability and serviceability (production-friendly)
Maintenance schedule (built into the manual)
The manual provides a frequency-based maintenance plan, for example:
• Before/after each use: visual check, watch for leaks, and release pressure so indicators read zero after operation.
• Monthly: check tubing/piping/fittings for leakage; clean system to keep dust/dirt free.
• Every 3 months: pump performance/leaks; clean filter and filter elements; re-torque fittings as needed.
• Every 6–12 months: full-pressure leak inspection; test/calibrate gauges/sensors/transmitters; replace hydraulic elements; verify valve/relief performance in-situ.
• Every 5 years: change major items like flow meter, relief valve, pressure control valve, motor, pump, etc.

Troubleshooting guidance (examples)
If pump runs but no pressure is indicated, the manual suggests checking return flow near tank, switching flow selection / DC valve via flow meter, partially closing needle valve before pressure line filter, and slowly tightening the pump relief.

8) Utilities and site requirements
Facilities required (as listed):
• Hydraulic oil: VG-46 or equivalent
• Power: 3-phase 415±5 V and 1-phase 220±5 V
• Proper earthing

9) Technical specification sheet 
Hydraulic supply & conditioning
• Max working pressure (system): 250 bar
• Main reservoir: 500 L (MS)
• Main pump: 46 LPM @ 250 bar (internal gear pump)
• Motor: 20 kW, VFD driven
• Duplex filtration: 10 μm + 5 μm, bypass, electrical + visual clogging indication
• Oil heating: 4 kW, 3-phase
• Cooling loop: 40 LPM pump + air radiator + filtered return

Measurement & sensors
• Pressure transmitter: 0–250 bar, 4–20 mA
• Flow meter: 5–50 LPM, test certified
• Pressure gauge: 0–280 bar, calibrated

Loading / clamping
• Inbuilt load sensing: 0–3000 kg
• Inbuilt LVDT in loading actuator: stroke per listed configuration
• Swing clamps (overload protected): 22.6 kN @ 200 bar and 13.9 kN @ 200 bar (listed variants)

Automation & HMI
• PLC/SCADA stack listed: Siemens IM151-8 PN DP CPU + WinCC flexible runtime (128 tags)
• Software supports process display, live values, graphs, storage/retrieval, and OK/NOT OK output

Technical specifications table (typical configuration)

  

    
Category
    
Parameter
    
Value / Description
  

  

    
Hydraulic supply (UUT)
    
Maximum working pressure
    
250 bar
  
  

    

    
Main pump type
    
Internal gear pump
  
  

    

    
Main pump rated flow
    
46 LPM (at rated speed)
  
  

    

    
Drive motor rating
    
20 kW, VFD-driven
  
  

    

    
Main reservoir capacity
    
500 L (MS)
  

  

    
Pressure control / protection
    
Relief & unloading
    
Setpoints as per test recipe
  

  

    
Flow & pressure measurement
    
Flow measurement range
    
5–50 LPM flow meter (test-certified)
  
  

    

    
Pressure measurement range
    
Transmitters up to 0–160 bar and 0–250 bar
  
  

    

    
Pressure indication
    
0–280 bar gauge (calibrated)
  

  

    
Filtration & cleanliness
    
Pressure filtration
    
Duplex filtration 10 µm + 5 µm
  
  

    

    
Filter condition monitoring
    
Electrical + visual clogging indication with bypass
  

  

    
Thermal management
    
Oil heating
    
4 kW heater, 3-phase
  
  

    

    
Oil cooling
    
Dedicated cooling loop with pump, air radiator & filtered return
  

  

    
Loading & clamping system
    
Loading pump
    
40 LPM, 210 bar (loading circuit)
  
  

    

    
Loading actuator sensing
    
Inbuilt LVDT & pressure sensor
  
  

    

    
Load measurement
    
Inbuilt load sensing up to 3000 kg
  
  

    

    
Clamping
    
Hydraulic swing clamps with overload protection
  

  

    
Automation & HMI
    
Control system
    
PLC-based sequencing with DAQ/SCADA supervision
  

Note: Values shown are the typical configuration for this rig family; model coverage, fixtures, and test recipes can be adapted to customer rear cover variants and acceptance limits.