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Underwater Scissor Lift Platform: 10m Proven Heavy-Duty 316L Design

Project Overview

This project covers the engineering, fabrication, and installation of a custom SJG11-5.0 Underwater Scissor Lift Platform designed for a state-level hydraulic engineering research laboratory. The platform is installed in a deep circular concrete test pit with a diameter exceeding 10 meters. Its primary operational function is to support heavy geological rock models, concrete dam mock-ups, and specialized hydraulic measuring instruments. By precisely controlling the vertical position of the platform, researchers can simulate varying water depths and hydrostatic/hydrodynamic conditions.

The environment requires the equipment to be fully or partially submerged in water for extended periods (exceeding 720 hours of continuous submersion per test cycle). This demands extreme corrosion resistance, zero fluid contamination, and high mechanical stability under eccentric hydraulic loads. The final acceptance criteria require a static leveling tolerance of

 $\leq \pm 5 mm$

across the entire 10-meter deck and zero drifting under maximum load over a 24-hour hold cycle.

Challenge & Solution

Challenge

Mechanical Topology & Load Distribution

This heavy-duty vertical transmission system is engineered for high-frequency continuous operation, transitioning seamlessly from a fully submerged base to a raised structural deck.

Structural Component	Engineering Specification & Function
10-Meter Circular Platform Deck	The primary load-bearing surface, configured for multi-directional material transfer or rotating alignment requirements.
Lock Struts (1 – 4)	A 4-point mechanical lock-pin mechanism designed to mechanically stabilize the platform deck upon reaching targeted elevation, completely relieving hydraulic or linkage stress under static load conditions.
Double-Span Scissor Linkage	The multi-stage scissor geometry mounted on a heavy-duty chassis, optimized to provide balanced force distribution across the 10-meter diameter span during the lifting stroke.
Pit Floor Submerged Base	The reinforced structural foundation embedded within the facility floor, allowing the circular platform to achieve zero-elevation flush alignment with the ground level when fully retracted.

Electrochemical and Pitting Corrosion in Long-Term Submersion: Standard carbon steel with industrial coatings will experience rapid coating failure and galvanic corrosion at pivot joints within months of continuous water immersion. Standard lubricants cannot be used as they wash out and pollute the testing water.
Structural Deflection of a 10m Cantilevered Span: A circular deck of 10,000 mm diameter supported by a scissor mechanism experiences extreme bending moments, especially under eccentric (off-center) loads when heavy rock models (up to 11 tons) are placed non-centrally. The structural deflection of the scissor legs must not compromise the $\pm 5 mm$ leveling tolerance.
Hydraulic Drift and Seal Integrity: Under sustained static load submerged underwater, standard single-seal cylinders leak hydraulic fluid into the water, while water ingress into the hydraulic system ruins the pumps. Furthermore, hydraulic valves naturally exhibit micro-leakage (drift), which would alter the simulated water depth during long-term (multi-week) research runs.
In-Water Height Position Feedback: Traditional optical or laser distance sensors cannot function underwater due to turbidity, light refraction, and suspended sediment. Standard rotary encoders on scissor pivots suffer from mechanical play and backlash, rendering them inaccurate for a $\pm 5 mm$ target window over a 5.3-meter stroke.

Solution

Hydraulic & Control Topology (Wet/Dry Segregation)

System Zone	Component	Engineering Specification & Signal Flow
Dry Room	Hydraulic Power Unit (HPU)	Supplies 21MPa rated hydraulic fluid flow. Output directed to wet-zone actuators.
Dry Room	PLC Control Panel + Dehumidifier	Central processing unit with active moisture control. Receives continuous position feedback signals.
Wet Environment	Double-Layer Sealed Cylinder	Primary linear actuator. Receives hydraulic power from HPU. Engineered for continuous operation in high-moisture/submerged conditions.
	Pilot-Operated Check Valves	Integrated with cylinders to prevent unintended descent under static loads or pressure loss.
	4x Hydraulic Latching Struts	Secondary mechanical locking mechanism driven by hydraulic pressure for position stabilization.
	Dual IP68 Draw-Wire Sensors	Redundant absolute position tracking. Transmits real-time displacement data back to the Dry Room PLC.

Full 316L Stainless Steel Metallurgy & Bushing Design:
The entire structural frame, scissor arms, platform deck (6mm plate), and handrails (21 posts with stainless chains) are fabricated from solid 316L stainless steel (EN 1.4404) [2]. Post-weld passivation was executed on all structural welds to restore the chromium oxide passive layer and prevent intergranular corrosion. All pivot joints are fitted with self-lubricating graphite-impregnated bronze bushings (no grease required), which utilize water as the natural lubricant.
Double-Span Single-Layer Scissor Geometry:
To counteract the bending moments of the 10-meter circular platform, we engineered a double-span, single-layer scissor linkage. This design distributes the load reactions across four primary structural rails instead of two, reducing structural deflection by 64% under worst-case eccentric load profiles.
Submersible Cylinders with Double-Layer Seal and Environmentally Safe Fluid:
The hydraulic cylinders are custom-made with 316L housings and hard-chromed duplex stainless steel rods. They feature a double-layer seal configuration (dual tandem polyurethane rod seals with an intermediate vent port). The system uses water-glycol fire-resistant/biodegradable hydraulic fluid; if a primary seal fails, zero mineral oil enters the test pool.
Zero-Drift Mechanical Fall-Arrest Lock Struts:
To eliminate hydraulic drifting over weeks-long test runs, we integrated four (4) heavy-duty, hydraulically operated telescopic locking struts . Once the platform reaches the specified target height, these mechanical struts extend radially or vertically to lock against the concrete pit floor/walls, transferring the static gravity load from the hydraulic fluid to solid mechanical columns.
Dual IP68 Draw-Wire Sensors & Closed-Loop PLC System:
Two redundant IP68-rated submersible draw-wire sensors are mounted diagonally under the deck. The sensors use high-tension Teflon-coated stainless steel wires to track the vertical travel directly. The analog signals (4-20mA) are processed by a Siemens S7-1200 PLC. The software monitors coordinate divergence; if the two sensors deviate by $> 3 mm$

, the PLC triggers an automatic tilt-correction algorithm through proportional flow control valves, maintaining a leveling tolerance of $\leq \pm 5 mm$ .
IP65 Control Cabinet with Dehumidification:
While the platform is submerged, the electrical control unit sits on the dry gallery. Due to high humidity from the water basin, the IP65 stainless steel cabinet is equipped with a active thermoelectric dehumidifier and anti-salt spray filters to protect the PLC, VFD, and safety relays from internal condensation.

Technical Specifications

Engineering Parameter	Metric Specification	Imperial Equivalent	Engineering Design Detail
Product Model	SJG11-5.0	SJG11-5.0	Custom underwater series
Platform Deck Shape	Circular	Circular	Diameter $D = 10, 000 mm$
Material Composition	316L Stainless Steel	316L Stainless Steel	Plate thickness $\geq 6 mm$ , passivation treated $\geq 6 mm$
Rated Dynamic Lift Capacity	$11, 000 kg$	$24, 250 lbs$	Lift capacity at $\geq 0.4 m/min$ speed
Max Static Distributed Load	$\geq 1, 000 kg/m^{2}$	$\geq 205 lbs/ft^{2}$	Total structure static limit $\approx 78, 500 kg$
Travel Stroke	$5, 300 mm$	$208.6 inches$	Height range: $1, 350 mm$ to $6, 650 mm$
Lifting Speed	$\geq 0.4 m/min$	$\geq 1.31 ft/min$	Controlled via proportional flow control valves
Leveling & Positioning Accuracy	$\leq \pm 5 mm$	$\leq \pm 0.197 inches$	Closed-loop feedback via redundant IP68 sensors
Deck Flatness Tolerance	$\leq \pm 5 mm$	$\leq \pm 0.197 inches$	Measured across 10m diameter under full load
Equipment Self-Weight	$\approx 32, 000 kg$	$\approx 70, 540 lbs$	Solid 316L structure, resists buoyancy forces
Hydraulic Fluid Type	Water-Glycol	Water-Glycol	Eco-friendly, non-flammable, zero bio-toxicity
Mechanical Lock Struts	4 Units	4 Units	Hydraulic telescopic mechanical locked columns
Removable Handrails	21 Posts / Spacing $1.5 m$	21 Posts / Spacing $4.9 ft$	316L steel with intermediate stainless link chains

Need a Technical Advice?

Underwater Scissor Lift Platform: 10m Proven Heavy-Duty 316L Design

Project Overview

Challenge & Solution

Challenge

Mechanical Topology & Load Distribution

Solution

Hydraulic & Control Topology (Wet/Dry Segregation)

Technical Specifications

Project Gallery

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