Hydraulic support synchronous action testing verifies that the columns, canopy, and advancing mechanisms of powered roof supports operate in coordinated motion under defined load and flow conditions, which is essential for structural integrity and operational safety in longwall mining faces. This article explains the testing principle, sample types, measurable parameters, evaluation methods, applicable standards, and typical applications of synchronization verification for hydraulic supports. Such testing is generally carried out by accredited third-party laboratories in accordance with the GB 25974 series, the EN 1804 series, and related ISO and IEC frameworks.
Technical Overview
Hydraulic supports, also known as powered roof supports or hydraulic chocks and shields, are the primary roof control equipment in modern longwall coal mining. Each support is a steel structure actuated by hydraulic columns, balance cylinders, and advance rams, and it repeats a working cycle of lowering, advancing, setting, and pushing the armored face conveyor forward. Synchronous action refers to the coordinated execution of these movements: both the left and right columns must extend and retract together, the canopy must remain essentially parallel to the base, the support must travel forward without skewing sideways, and the conveyor must be advanced evenly along the face line.
Asynchronous movement creates uneven load distribution, column bending, accelerated seal wear, canopy tilt, jamming of the support against neighboring units, and, in severe cases, localized roof deterioration that endangers face personnel. Synchronous action testing therefore quantifies displacement differences, timing differences, and angular deviations during each phase of the support cycle, providing objective evidence that the hydraulic circuits, mechanical linkages, and control system are correctly matched. Testing is performed on dedicated rigs under both no-load and simulated resistance conditions, in both manual and electro-hydraulic automatic modes.
- Coordinated extension and retraction of all hydraulic columns
- Maintenance of canopy-to-base parallelism during lowering and setting
- Straight, skew-free advancement of the support along the face
- Even pushing of the face conveyor by the advance rams
- Consistent group-action timing across adjacent supports under electro-hydraulic control
Testing Samples
Complete Hydraulic Support Assemblies
Full shield, chock-shield, and frame-type supports of two-leg, four-leg, or six-leg configuration, tested as delivered from production, after overhaul, or as prototype units under type evaluation. Testing on the complete assembly captures the combined behavior of the hydraulic circuits, mechanical structure, and control system.
Hydraulic Columns, Jacks, and Balance Cylinders
Individual actuators are tested in pairs or groups to characterize stroke consistency, internal leakage, extension speed, and pressure holding capability, all of which directly influence synchronization performance when the actuators are installed on the support.
Electro-Hydraulic Control Components
Solenoid valve groups, pressure and displacement sensors, controllers, and communication interfaces are evaluated for response time, command accuracy, and timing dispersion, because even small delays in valve opening or signal transmission translate into measurable synchronization error at the support.
Advance and Pusher Mechanisms
Pusher arms, advance rams, and articulation joints are tested to confirm that the conveyor is advanced without lateral deviation and that the reaction forces do not distort the support base during the pushing stroke.
Support Groups and Face Line Sections
Multiple interconnected supports equipped with group-control functions are tested to verify automated neighbor actions, such as paired or alternate advancement sequences, and to confirm that cumulative timing errors along the face remain within acceptable limits.
Testing Items
Typical measurable items and acceptance criteria for synchronous action testing include the following, with numeric limits taken from the applicable product standard or the agreed technical specification:
- Displacement difference between left and right columns during synchronized lowering and raising
- Time difference between the start and completion of column actions on each side
- Canopy inclination angle relative to the base throughout the full working cycle
- Lateral skew and straightness deviation of the support during advancement
- Parallelism and stroke consistency of paired advance rams when pushing the conveyor
- Total completion time and cycle time for lowering, advancing, and setting at rated pressure and flow
- Pressure consistency between column circuits and between supports during group actions
- Synchronization error in automatic electro-hydraulic sequences versus manual operation
- Response and release times of control valves and sensors affecting action coordination
- Stability of movement, including sticking, surging, or oscillation during travel
Testing Methods
Displacement Synchronization Measurement
Draw-wire displacement sensors, laser rangefinders, or optical encoders are mounted symmetrically on the columns and on reference points of the base and canopy. Continuous displacement-time curves are recorded for each measurement point, and the synchronization error is calculated as the maximum instantaneous or end-of-stroke difference between paired channels. The resulting deviation is expressed in millimeters or as a percentage of stroke and compared with the specified limit.
Pressure and Flow Monitoring
Pressure transducers installed at column ports, pilot lines, and the supply circuit reveal whether both sides of the support receive equal hydraulic energy. Flow meters and pump station records are used to confirm that tests are conducted at the rated supply pressure and flow, since synchronization behavior can change significantly under different flow conditions.
Timing and Sequence Analysis
The test protocol commands a complete working cycle, and the data acquisition system timestamps valve commands, sensor responses, and motion start and stop events on each side of the support. The differences between these timestamps quantify the timing dispersion of the hydraulic circuits and the control system, and the total cycle time is compared against the specified maximum.
Angular and Geometric Deviation Measurement
Bidirectional inclinometers mounted on the canopy and base measure tilting during lowering, advancement, and setting, while calibrated references and linear measurements record lateral skew of the support relative to the face line. Video measurement or photogrammetry may supplement these readings to document trajectory straightness.
Test Conditions and Data Acquisition
Testing is performed under no-load conditions and under simulated roof resistance using a reaction frame or loading rig, in both manual and automatic control modes. All channels are sampled by a synchronized high-frequency data acquisition system, and dedicated software generates displacement, pressure, and time histories from which synchronization indices are computed. Test procedures follow the general requirements of the GB 25974 series for hydraulic supports, the EN 1804 series for hydraulic chocks, shields, and their control systems, and the hydraulic fluid power safety rules of ISO 4413, together with relevant ISO and IEC standards for the electronic control equipment.
Applications
Synchronous action testing serves multiple stages of the equipment life cycle and multiple stakeholders in the mining industry:
- Type testing and factory acceptance testing of new hydraulic support models prior to serial production
- Compliance verification and certification support against GB, EN, ISO, and IEC requirements
- Quality control of repaired or overhauled supports before return to service underground
- Commissioning verification of electro-hydraulic automation systems at mine sites
- Research and development validation of new column, valve, and control system designs
- Periodic inspection and condition assessment as part of mine equipment safety management
FAQ
What is hydraulic support synchronous action testing?
It is a systematic performance evaluation that measures how uniformly the columns, canopy, advancing mechanism, and conveyor pusher of a hydraulic support move during the lowering, advancing, and setting cycle, quantifying displacement differences, timing differences, and angular deviations against defined limits.
Why is synchronization so important for hydraulic supports?
Uneven movement causes asymmetric loading of the columns and structural members, accelerates seal and guide wear, tilts the canopy, and can jam the support against adjacent units. Over time this degrades support capacity and creates roof control risks, so synchronization is treated as a key safety and reliability indicator.
What parameters are measured, and what are typical acceptance criteria?
The main parameters are the displacement difference between paired columns, the time difference between corresponding actions, the canopy inclination angle, lateral skew during advancement, and total cycle time. Acceptance limits, usually expressed as a few millimeters of displacement difference, a small angular deviation, and a maximum cycle duration, are defined by the applicable standard or the technical specification agreed for the project.
Can the test be performed on site as well as in a laboratory?
Yes. Laboratory rigs provide controlled loading and precise instrumentation for type and acceptance testing, while portable sensors and data acquisition equipment allow on-site commissioning and periodic checks using the mine hydraulic supply, although measurement uncertainty on site is generally higher.
Which standards govern this testing?
The GB 25974 series covers general technical requirements for hydraulic supports, the EN 1804 series addresses hydraulic chocks, shields, and their hydraulic control systems, and ISO 4413 specifies hydraulic fluid power general and safety rules, with additional ISO and IEC standards applying to the electronic control components.
How long does a typical synchronous action test take?
A single complete cycle test can be completed in a few minutes, but a full evaluation involving sensor installation, no-load and loaded runs, manual and automatic modes, and repeated cycles for repeatability typically requires from one to several days depending on the number of supports and the scope of the test program.
