I. Background
PVC-U four-hole pipe with **“2 big and 2 small” symmetric structure** (2 Φ40mm main holes + 2 Φ25mm sub-holes, as shown in Fig. 1) has become a cost-effective choice for the scenarios of cellular communication and park power. Compared with single-hole pipe, its synchronized cable threading efficiency is increased by 60%, but it is found in the project:
Cable friction resistance is too large when threading (47% of construction complaints)
Rainy season water inside the pipe drainage is not good (resulting in cable corrosion accounted for 32%)
Second, the core problem: runner structure defects analysis
Through the cable traction test (refer to YD/T 1113-2019) and drainage simulation (ISO 9001 standard), four major defects of the traditional four-hole pipe runners are found:
Problem type Conventional design performance Impact consequences
Sharp corners Angle between sub-pipes 90°±5° Cable bend radius <10D (standard requirement ≥15D)
Sudden change in wall thickness Difference in wall thickness at the main / sub-pipe connection > 0.8mm Formation of local drag coefficient ξ = 0.7
Section unroundness Ellipticity＞5% Effective flow area is reduced by 12%.
Inner wall roughness Ra=1.6μm (standard≤1.0μm) Drag coefficient increases by 23%.
Fluid mechanics optimization experiments
1. Optimization of cross-section shape (CFD simulation)
ANSYS Fluent is used to simulate the drag coefficient (λ) and flow coefficient (μ) for different cross-section shapes:
Cross-section type Equivalent diameter (mm) Drag coefficient λ Flow coefficient μ Material consumption (kg/m)    
Square 33.5 0.024 0.82 3.2    
Rounded square 34.2 0.018 0.91 3.3 (optimal solution)
Round 32.0 0.020 0.88 3.5    
Key improvements:
Angle between sub-tubes changed from 90° to 150° chamfered (Fig. 2)
R5mm rounded transition in the main/subtube transition area.
2. Inner wall treatment process
Comparison of the surface properties of the different treatments through nano-coating experiments:
Process type Roughness Ra (μm) Coating adhesion (grid method) Weathering resistance (1000h aging)
Normal Extrusion 1.5-1.8 5B Layer Peeling
Nano TiO₂ Coating 0.6-0.8 4B Gloss Retention 92
IV. Engineering Solutions
1. Fluid performance improvement standard
According to the optimization results, formulate enterprise internal control standards (higher than GB/T 18477.1):
Indicator National standard requirements Optimized standard Test method
Cable pulling tension (N) ≤500 ≤350 YD/T 1113-2019
Drainage flow rate (L/min) - ≥120 Homemade water pressure test device
Inner wall friction coefficient - ≤0.12 ASTM D3330
2. Construction support program
“Trinity” threading method to reduce construction resistance:
Pre-lubrication: Spraying water-based silicone lubricant inside the pipe (40% reduction in coefficient of friction).
Guide: use of a four-hole synchronized traction head (Figure 3).
Air flow assistance: compressed air blowing assistance (wind speed ≥ 5m / s)
V. Test case: a smart district project
Indicator Traditional four-hole pipe Optimized four-hole pipe Improvement effect
Single-hole cable threading time 12 minutes 7 minutes -42
Drainage time of water accumulated in the pipe 8 hours 2.5 hours -69
Wear rate of cable jacket 15% 3% -80
Extension of cutting-edge technology
1. Bionic runner design
Drawing on the micro-groove structure of sharkskin (Figure 4), it can further reduce the coefficient of friction by 15%.
2. Intelligent piping system
Integrated micro-pressure sensor for real-time monitoring:
Dynamic tension changes during threading (early warning of blockage)
Water level in the pipe (linkage to drainage pump)
Conclusion
This paper solves the industry pain point of difficult threading and slow drainage of four-hole pipe through hydrodynamics-driven structure optimization. As a professional supplier, we offer:
✅ Customized flow channel design service
✅ Threading resistance simulation and calculation tool
✅ Drainage performance third-party test report
Keywords: PVC-U four-hole pipe, hydrodynamics, threading efficiency, drainage capacity, communication pipe