Adjustable gas spring technical
Adjustable Gas Spring – Technical Overview
Here's a technical breakdown of adjustable gas springs (gas struts), covering their operation, types, adjustment mechanisms, key specifications, and applications:
Adjustable Gas Spring Core Principle
Basic Function: A sealed cylinder filled with pressurized nitrogen gas. A piston rod attached to a piston moves through the cylinder. Oil fills the space below the piston for damping.
Force Generation: The pressurized gas exerts force on the piston rod, attempting to extend it. The force (F) is primarily calculated as: F ≈ P * A
P = Gas pressure inside the cylinder
A = Effective cross-sectional area of the piston rod
Damping: Oil flows through precisely designed orifices/valves in the piston as the rod extends or retracts, controlling the speed of movement.
What Makes Them "Adjustable"
The key difference from standard gas springs is the ability to modify their force/stroke/locking behavior after manufacturing and installation, without disassembly.
Types & Adjustment Mechanisms
Force-Adjustable Gas Springs:
Mechanism: A needle valve or screw mechanism accessible (usually via a small hole or hex key) at the rod end or cylinder end.
How it Works: Turning the adjustment screw moves a needle that partially blocks or opens the oil flow path through the piston orifice.
Effect: Modifies the damping force, primarily during extension.
Clockwise (Closing): Increases resistance, slows down extension speed.
Counter-Clockwise (Opening): Decreases resistance, speeds up extension speed.
Limitation: Does not significantly change the basic extending force (F ≈ P * A). Primarily controls speed via damping.
Stroke-Adjustable Gas Springs:
Mechanism: A threaded collar or locking ring on the cylinder body.
How it Works: The collar physically limits how far the rod can retract into the cylinder. Rotating the collar changes its position along the cylinder's threads.
Effect: Changes the minimum length (retracted length) of the gas spring, thereby altering its usable stroke (Extended Length - New Retracted Length).
Use Case: Fine-tuning the fully closed position of a lid, door, or panel after installation.
Lockable Gas Springs (Position-Locking):
Mechanism: An integrated valve system activated by pulling/pushing a lever/button on the rod end fitting or via a cable. More complex internal design.
How adjustable gas spring Works:
Mechanical Locking: A pin or latch physically blocks the piston rod's movement.
Gas Transfer Locking (Most Common): Activating the lever opens a bypass valve connecting the gas chambers above and below the piston. This equalizes pressure, eliminating the extending force and allowing the rod to move freely (or lock at any position). Releasing the lever closes the bypass, restoring gas pressure difference and extending force.
Effect: Allows the adjustable gas spring to be "switched off" (free movement/locked position) or "switched on" (damped extension support).
Variations: Can be locking in compression, extension, or both. Some lock only at the end of stroke.
Key Technical Specifications
Force (F): Usually measured in Newtons (N) or pounds-force (lbf). Critical for supporting the load. Specified at a standard rod position (e.g., 10mm extended).
Extended Length (L1): Length from center of end fitting to center of end fitting when fully extended.
Stroke (S): Length the rod travels (L1 - L2).
Retracted Length (L2): Length from center of end fitting to center of end fitting when fully retracted. Adjustable in Stroke-Adjustable types.
Diameter: Cylinder outer diameter (OD) and Rod diameter.
Mounting Fittings: Ball studs, clevises, pins, etc. (Specify thread size, ball diameter, width).
Force Tolerance: Allowable variation from nominal force (e.g., ±5%, ±10%).
Operating Temperature Range: Limits for reliable performance.
Damping Speed: Often specified as extension/compression speed under a specific load (mm/s).
Gas Pressure: Internal pressure (typically high, e.g., 50-200 bar).
Cycle Life: Expected number of full extension/retraction cycles before performance degrades significantly.
Applications (Where Adjustability is Crucial)
Office Furniture: Chair height adjustment (Locking), adjustable monitor arms (Force/Speed).
Industrial Machinery: Safety guarding (position locking for maintenance), adjustable workstations (force/speed/stroke).
Automotive: Hood/trunk struts (force/speed), adjustable tailgates, RV steps/stabilizers (locking/stroke).
Medical Equipment: Adjustable patient tables, surgical lights, imaging equipment arms (precision force/speed/locking).
Aerospace: Cargo doors, access panels (locking/stroke).
Material Handling: Lift-assist arms for tools/components (force/locking).
Selection & Design Considerations
Force Calculation: Calculate the required force based on the weight, geometry (leverage/moment), and desired motion (e.g., opening effort). Factor in safety margins.
Mounting Geometry: Position significantly impacts force required and motion smoothness. Mounting points should allow smooth rod movement without binding.
Adjustment Need: Determine what needs adjusting post-installation (Force/Speed? Stroke? Locking?).
Environment: Temperature, humidity, chemicals, dust. Seal compatibility is vital.
Safety: Adjustable gas spring contain high pressure. Never heat, weld, drill, or dispose of in fire. Follow manufacturer handling instructions. Use locks/stops for safety-critical applications.
Quality: Opt for reputable manufacturers. Poor seals lead to leaks and failure.
Adjustable gas springs provide essential flexibility in design and fine-tuning, making them invaluable where precise control over motion, position, or force is required after installation. Understanding the different adjustment types and their mechanisms is key to selecting the right component.
