1. Easy to Install

A lock‑type gas spring arrives as a sealed, pre‑charged unit. With standard ball studs, clevises or eye ends, it bolts directly into existing frames — no hydraulic lines, no external power, no calibration. Most OEM lines complete installation in under 60 seconds per unit.

2. Easy to Use

End users operate the spring through a simple lever, cable or button that actuates the release pin. One hand controls both movement and locking, which is why the mechanism dominates hospital beds, hairdressing chairs and passenger seats where intuitive, glove‑friendly operation is mandatory.

3. No‑Step (Stepless) Adjustment

There is no stepped adjustment. Stop and locking can be set at any arbitrary point of the stroke by opening and closing the internal oil (gas) passage. This gives infinite intermediate positions — a chair backrest or bed section can rest at 17°, 18.5° or any angle the user chooses.

Free Piston Design

A floating free piston separates the nitrogen gas chamber from the oil chamber. This keeps gas from emulsifying into the oil, delivers very smooth damping, stable locking stiffness in both rod‑up and rod‑down orientations, and superior performance in large‑stroke springs (200–350 mm). Recommended for hospital beds and premium ergonomic chairs.

Encapsulated Piston Design

The encapsulated piston integrates the sealing and valve functions into a compact cartridge. It offers a shorter closed length, simpler manufacturing and excellent cost efficiency for medium strokes (50–200 mm), making it the workhorse for office chairs, rocking chairs and beauty parlor chairs where price‑performance ratio is critical.

Nitrogen Pressure Chamber

Charged to 20–200 bar, nitrogen stores the energy that extends the rod. Force F1 is proportional to charge pressure × rod area, which is why a Ø14 mm rod can output 3,500 N while a Ø6 mm rod outputs 450 N. Andefu tunes charge pressure per order in 5 N increments.

Locking Valve & Release Pin

The heart of the locking mechanism. A spring‑loaded valve seats against a precision‑lapped orifice; the external release pin (cable, lever or button) unseats it. Valve seat geometry determines locking stiffness: rigid valves trap oil absolutely, elastic valves permit a controlled micro‑bypass for cushioned holding.

Oil Circuit & Seal Package

Hydraulic oil lubricates the seal package and transmits the lock. Multi‑lip rod seals, O‑rings and wear rings are selected for 50,000+ cycles and −30 °C to +80 °C operation. Seal quality is the single biggest differentiator between a spring that locks for 10 years and one that drifts after 6 months.

Static Holding Force (N) vs Rod Diameter — Andefu Lock‑Type Series

Holding force scales with rod cross‑section and charge pressure. For dynamic or shock loads, apply a 1.5× safety factor when specifying.

What to Look For When Specifying

• Holding force ≥ 1.5× max static load at the weakest mounting angle
• Locking drift < 2 mm after 10 min under rated load
• Release force 20–60 N at the pin for comfortable actuation
• Cycle life ≥ 50,000 with force decay < 10%
• Operating temperature −30 °C to +80 °C with stable oil viscosity
• Salt‑spray resistance ≥ 96 h (ASTM B117) for chrome‑plated rods

The lock‑type hairdressing chair remains the reference application: one spring, one pedal, infinite positions — for 10+ years of service.

Define Load & Holding Force

Calculate the worst‑case static and dynamic load at the seat/bed surface, convert to axial force on the spring using lever geometry, and apply a 1.5× safety factor. This selects the rod diameter (Ø6–Ø14 mm).

Choose Rigid or Elastic Locking

Need zero drift under clinical or professional loads? Choose rigid. Need cushioned, body‑conforming hold for rocking chairs and recliners? Choose elastic. Andefu supplies both valve types in the same envelope.

Select Stroke & Piston Construction

Stroke defines closed/extended length. For strokes above 200 mm or mixed mounting orientations, specify the free piston design; for compact, cost‑sensitive chairs, the encapsulated piston is optimal.

Specify Ends, Release & Accessories

Ball studs, clevises, eye ends; cable, lever or button release; optional protective sleeve for salon environments. Release routing is the most‑overlooked design item — involve Andefu early.

Validate with Samples & Cycle Testing

Never release to production on a datasheet alone. Run 5,000‑cycle pilot tests at your plant; Andefu provides free samples, force curves and installation drawings for validation.

Lock In QC Agreement & Warranty

Agree AQL sampling, batch force traceability and warranty terms (24 months standard). Serialized batches make any field issue traceable to a production lot.

Installation & Handling

Mount per the specified orientation (rod‑down unless the free‑piston version states otherwise). Avoid side loads on the rod, never paint or weld the tube, and do not rotate the rod against a locked valve. Use the supplied release force — never pliers.

Inspection & Service Life

Annually check for locking drift, oil film staining at the rod seal, and corrosion. A properly specified Andefu spring exceeds 50,000 cycles; most field units are replaced only when the host furniture is retired.

Standards & Compliance

Production under ISO 9001:2015; materials RoHS/REACH compliant; rod salt‑spray tested to ASTM B117. End‑product support documentation available for BIFMA X5.1 (office chairs) and IEC 60601‑1 (medical beds) assessments.