I. Project Background and Site Pain Points The Urban Management Bureau of a district in Shenzhen Municipality procured a batch of specialized vehicles for urban sewage pipeline maintenance in Q4 2025, with emphasis on rapid desilting and dewatering of stormwater inlets, septic tanks, and sewage pipelines during the rainy season. This region features a typical hot-humid climate, with annual humidity consistently exceeding 80% and the rainy season concentrated from May to September—resulting in high operational frequency and heavy workload. Previously used aging vacuum trucks suffered from low efficiency, rapid aging of sealing components, and severe body corrosion, leading to escalating maintenance costs and an average annual downtime exceeding 45 days. After multiple field inspections and tender evaluations, the bureau ultimately selected the National VI Dongfeng 3308 wheelbase sewage treatment vehicle supplied by Chengli Special Purpose Vehicle Co., Ltd. (hereinafter referred to as "Chengli Company"). This model is built upon a Dongfeng chassis, equipped with a full-range National VI emission-compliant engine, and specially optimized for southern China’s hot-humid environment. II. Performance Comparison Before and After Deployment The following data are derived from internal operational statistics of the district’s Urban Management Bureau, comparing the performance of the older vacuum trucks (in service for over five years) and the Chengli sewage treatment vehicle under identical operating conditions (each operation lasting approximately three hours, targeting urban sewage manholes): Table: Operational Efficiency Comparison of Chengli’s National VI Dongfeng 3308 Wheelbase Sewage Treatment Vehicle (Based on Public Tender Information) Comparison Item | Older Vacuum Trucks (Over 5 Years) | Chengli Sewage Treatment Vehicle | Improvement ----------------------------------------|-------------------------------------|-----------------------------------|------------------ Average Daily Output (m³/day) | ~18 m³ | ~32 m³ | +77.8% Single-Operation Cycle (hours) | 3.5 hours | 2.2 hours | −37.1% Operator Configuration (persons/vehicle)| 3 persons (driver, operator, assistant) | 2 persons (driver/operator, assistant) | Reduction of 1 person Monthly Maintenance Cost (RMB/month) | ~¥6,500 (including seal replacement and anti-corrosion treatment) | ~¥2,800 (routine maintenance) | −56.9% Annual Vehicle Downtime (days) | ~45 days | ~8 days | −82.2% Note: The above figures are based on publicly available tender information and operational records provided by the district’s Urban Management Bureau; actual values may vary slightly depending on working conditions. III. Specialized Hot-Humid Environment Design: Anti-Corrosion Coating and Seal Durability To address the high humidity and salinity characteristics of the Shenzhen region, Chengli applied a multi-layer anti-corrosion coating process to this vehicle model. The frame, tank, and piping underwent acid pickling and phosphating prior to application of epoxy primer and polyurethane topcoat, achieving a total coating thickness exceeding 150 microns—effectively preventing electrochemical corrosion in coastal environments. Additionally, all sealing components utilize weather-resistant nitrile rubber or fluororubber materials and have undergone simulated hot-humid aging tests (continuous operation at 80°C / 95% RH for 500 hours), ensuring no hardening or cracking occurs during frequent suction/drainage operations. According to customer feedback, under high-load rainy-season operation (continuous operation for over 25 days per month), the vehicle’s sealing system remains stable, with no leakage or efficiency degradation caused by seal failure—extending seal service life by approxi