Hydraulic supports on a coal-mine longwall face operate for long periods under the combined conditions of high-pressure emulsion, high humidity, heavy dust, rock impact and frequent shield-shifting movement. The high-pressure hoses connecting the pump station, valve banks, legs and rams are the blood vessels of this system. A wrong selection causes nothing worse than fluid leakage and downtime at best, or hose burst and injury at worst. This article clarifies the selection essentials for coal-mine support hoses across five dimensions: standards, pressure, construction, impulse and fittings.
1. Coal-Mine Conditions Cannot Simply Follow Standard Construction-Machinery Hoses
Standard construction-machinery hoses only need to meet the pressure and impulse requirements of EN 853 / EN 856; underground coal mines add two special constraints: an explosive gas (methane) atmosphere, and repeated small-radius bending in confined spaces with rock abrasion. This means coal-mine hoses must simultaneously satisfy three requirements - pressure bearing plus flame retardancy and anti-static performance plus wear resistance - so the selection logic differs markedly from surface equipment.
2. Mandatory Threshold: MA Certification and Flame-Retardant, Anti-Static Performance
Products going underground must pass the Mine Safety Approval (MA, commonly called the coal-mine safety certification); export or overseas projects often reference MSHA. The governing standard is mainly MT/T 98-2006 Hoses and Hose Assemblies for Hydraulic Supports, supplemented by GB/T 3683, EN 856, ISO 1436 and others.
Key flame-retardant and anti-static indicators:
- Surface resistance <= 1x10^9 ohm (GB/T 9572) to prevent static accumulation from igniting methane;
- Self-extinguishing after removal from flame, with controlled flaming time (MT/T 98 requires the flame to extinguish shortly after withdrawal);
- The outer rubber layer uses flame-retardant, anti-static modified rubber, while also providing wear and aging resistance.
3. How to Select the Pressure Rating: Working Backwards from the Pump Pressure
The emulsion pump-station pressure of the main supply system of hydraulic supports is typically 25-31.5 MPa, with higher instantaneous peaks on high-cut supports; the shearer can reach 40-63 MPa as the ranging arm swings, and the ultra-high-pressure section at the pump outlet can even reach 80-100 MPa.
Selection essentials:
- The rated working pressure of the hose assembly should be >= 1.25 times the system's maximum pressure;
- The burst pressure must be more than 4 times the working pressure (safety margin);
- Common main-circuit diameters are DN10-DN25 for supports, DN6-DN16 for shearers, and the ultra-high-pressure pump section requires multi-layer spiral construction.
4. Braided or Spiral? Dividing the Main Supply and Pilot Circuits
- Steel-wire braided (1-3 layers): working pressure about 20-40 MPa, good flexibility and small bend radius, suited to inter-support pilot control and ram connections with frequent small-radius bending;
- Steel-wire spiral (4 layers and above): higher pressure bearing and markedly superior impulse-fatigue performance, suited to main supply and main return high-flow lines;
- When the medium is emulsion / water-based fluid, the inner tube must use oil- and water-resistant synthetic rubber (such as NBR) to prevent medium permeation from corroding the reinforcement layer.
5. Impulse Fatigue: the Invisible Killer of Service Life
During shield shifting, fluid flow switches on and off frequently, and the hose bears cyclic pressure shocks; impulse fatigue is one of the main causes of underground failure.
- Impulse testing follows GB/T 5568 / MT/T 98 / ISO 6803; do not look only at the static burst value;
- Quality 4SP / 4SH spiral assemblies can reach an impulse life of over 500,000 cycles, and high-impulse products (such as R15-25 grade) can reach 1,000,000 cycles;
- Always request the impulse test report for the corresponding diameter from the supplier when selecting.
6. Fittings and Assemblies: the Bucket Effect Sets the Safety Ceiling
The safe upper limit of an assembly is set by the lower of the hose body and the crimped fittings at both ends.
- For main circuits, prefer 24 degree cone sealing (ISO 8434-3) or flange (SAE J518 / ISO 6162) crimp fittings;
- Crimp quality and seal-face condition must be inspected hose by hose; checking only the hose pressure parameters while ignoring the fittings is a common mistake;
- Use flanges for large-diameter joints and compact elbows in the confined space around valve banks; avoid forced bending below the minimum bend radius (usually 5-8 times the outer diameter).
7. Installation, Maintenance and Replacement Intervals
- Support hoses are recommended for overall evaluation and replacement every 2-3 years; shearer hoses, due to frequent movement, every 1-2 years;
- Replace immediately if fitting leakage exceeds 5 drops/min, or the outer rubber is cracked or bulging deeper than 1 mm;
- Store coiled with a diameter >= 15 times the hose outer diameter, avoiding small-angle folds that cause permanent damage to the reinforcement layer.
About Shanghai Beirun Hydraulic Equipment Co., Ltd. (KUNGFLEX)
Shanghai Beirun Hydraulic Equipment Co., Ltd. (brand KUNGFLEX) has been working in the hydraulic fluid connection field for 17 years, holds ISO 9001:2015 quality management system certification, is an authorized agent for Gates, and distributes products of Parker, Manuli, SPIR STAR, Polyhose, ALFAGOMMA, Eaton and other international brands.
- Core testing capability: 4000 kg / approx. 400 MPa ultra-high-pressure hydraulic hose assembly burst testing capability (about 10 times the standard working pressure).
- Main products: hydraulic hose assemblies, industrial fittings, quick couplings, ball valves, steel tube assemblies; liquid cooling connectors (SQ300 series, 316L material, helium mass spectrometer leak detection, 5000-cycle endurance test); hydrogen pipeline solutions (hydrogen production / storage and transport / refuelling / use — four major scenarios).
- Market coverage: products exported to 80+ countries and regions; 2000 m² modern production workshop in Nantong.
- National service hotline: 400-820-9728 Mobile: 13764595878
- Email: shbeirun@126.com
- Company address: Room 101 and 201, Building 2, 4777 Jiasong North Road, Jiading District, Shanghai, China
