Cosmos Pumps supplied CDW Ultra High Head submersible dewatering pumps to a national railway tunnel project in North India, where groundwater inflow against discharge heads exceeding 155 metres and abrasive rock-fine contamination ruled out every standard-head pump option on the contractor’s approved list. Over 18 months of active tunnelling, the units maintained continuous dewatering while removing a total of 74,000 cubic metres of groundwater over the full project period.
Written by Cosmos Pumps Engineering Team
The Challenge
The railway tunnel passes through a section of the Himalayas in North India with highly fractured geology and sustained groundwater pressure. The tunnel sections push through rock at depths where the vertical distance from water inflow points to discharge at the tunnel portal exceeds 155 metres. Standard-head submersible pumps — rated to 86 metres maximum shut-off head — cannot deliver flow at this head. High-head variants rated to 140 metres were also below the site requirement at the deepest working faces.
The civil contractor faced three compounding problems:
First, the head requirement alone was disqualifying for most pump suppliers. At 140 metres working head, the available pool of submersible pump models capable of delivering usable flow narrows sharply.
Second, the groundwater carried rock fines from drilling and blasting operations at specific gravity above 1.0 with particle sizes up to 8 mm. This abrasive load destroys standard pump impellers faster than the already constrained service intervals that remote site access permits. At this altitude and location, a pump requiring workshop repair has a lead time measured in days.
Third, the confined tunnel geometry imposed dimension constraints. Pumps had to fit within working galleries that also accommodate tunnelling operations and tunnel transport — oversized equipment was not viable regardless of performance.
Our Solution
Cosmos Pumps supplied 6 units of the CDW Ultra High Head submersible dewatering pump — the company’s 2-stage design rated for shut-off heads of 90 to 200 metres, built specifically for the head ranges encountered in mine and tunnel dewatering that standard models cannot serve.
The Ultra High Head’s 2-stage SS316 impellers addressed the abrasion problem directly. The SS316 material provides corrosion resistance against the slightly acidic groundwater chemistry common in Himalayan geology, while the 2-stage design distributes the hydraulic load across two impeller stages, reducing wear-per-stage compared to a single-stage unit at the same total head.
Viton rubber seals — standard on the Ultra High Head range — provided additional chemical resistance. The dual SiC vs SiC mechanical seal configuration, combined with a backup oil seal, gave the contractor redundancy at each seal stage: a condition the Cosmos team recommended as non-negotiable given the site’s replacement lead times.
Cosmos dispatched a field technician to the tunnel portal for commissioning and initial operation. The technician conducted a calibration run at each active face, confirmed flow rates against calculated groundwater inflow volumes, and certified the contractor’s site maintenance team on field seal replacement. A pre-positioned spare parts depot — including impeller sets, mechanical seals, and oil seal assemblies — was established at the nearest railhead depot to give the site same-day replacement capability without waiting for parts from Faridabad.
Pump Specification
| Parameter | Value |
|---|
| Pump model | Cosmos CDW Ultra High Head Submersible Dewatering Pump |
| Units deployed | 6 |
| Working head at site | 140 metres |
| Flow rate achieved | 960 LPM (57.6 m³/h) at working head |
| Shut-off head capacity | 90 M – 200 M (2-stage) |
| HP per unit | 75 HP |
| Impeller material | SS316 (2-stage) |
| Mechanical seal | Dual SiC vs SiC + oil seal backup |
| Seal material | Viton rubber (acid and abrasion resistant) |
| Insulation | Class H (180°C) with thermal sensor |
| Shaft material | SS431 high-torsional-strength shaft |
| Cable length | 20 m standard |
| Installation | Vertical and horizontal |
Results
Over 18 months of active tunnelling, the CDW Ultra High Head units maintained continuous dewatering without an unplanned excavation stoppage attributable to pump failure. Measured outcomes:
- Total groundwater removed during active excavation: 74,000 m³
- Longest continuous pump run before planned maintenance: 720 hours
- Unplanned downtime events attributable to pump failure: 0
- Mechanical seal service intervals achieved: 800 hours — more than twice the contractor’s 350-hour baseline from earlier tunnel sections with different pump makes
The dual SiC mechanical seal ran to 800 hours before first replacement — more than double the contractor’s expected interval based on prior tunnel sections, reducing seal replacement labour at a location where unscheduled maintenance has a measurable impact on programme.
“The CDW Ultra High Head was the only model on the market that could deliver usable flow at this head. The pre-positioned depot and on-site commissioning support were what made the risk acceptable at a location where getting a replacement pump takes days, not hours.”
— Dewatering Project Manager, Civil Infrastructure Contractor, North India
CDW Ultra High Head specifications: cosmospumps.com/cosmos_pumps/dewatering-pump-cdw-ultra-high-head/
Where slurry conditions apply: Cosmos CSL Slurry Pump
For tunnel and mine dewatering project enquiries: +91 99333 22238 | cosmos@cosmospumps.com
