Gas lift classes, tilt units and seat plates on swivel chairs

Swivel lounge chairs are seat shells bolted to a stack of moving parts. That stack is 18 to 28 per cent of the ex-works price and it generates roughly 90 per cent of the parts claims we see in the field.

Published by JPChairs · Chair manufacturer in Foshan, China · 2026-10-20

What you are actually buying

Five assemblies sit between the seat shell and the floor, and each one has its own specification line on the purchase order.

• Gas cylinder: the chrome or black column that sets seat height, 50 mm outer diameter on most units, with a stroke of 80 to 160 mm.
• Seat plate: 2.0 or 3.0 mm pressed steel. It is the interface between the shell and the mechanism, and it decides whether a replacement unit still fits years later.
• Tilt and swivel unit: the hinged body carrying the tension spring, the recline lock and the height lever.
• Base and castors: a 640 to 700 mm five-star base with castors of 50 to 65 mm in nylon or polyurethane.
• Cost share: the mechanism assembly is 18 to 28 per cent of the ex-works price of a swivel lounge chair and about 90 per cent of the parts claims in a mixed fleet.

Gas lift classes and stroke

Gas cylinders are graded by the load they carry, and the grade has to be named on the order. Left open, you get whatever the mechanism supplier had on the shelf.

• Class 3: rated to 120 kg of user and load. The standard for hotel bedrooms, lobbies and occasional seating.
• Class 4: rated to 150 kg, with a thicker wall and a larger piston. It costs USD 3 to 7 more per chair and is what we fit for venues running beyond 8 hours a day.
• Stroke: 80 mm on a low lounge unit, 100 to 120 mm at desk height, 140 to 160 mm on a bar-height unit. A 100 mm stroke gives roughly a 430 to 530 mm seat height range.
• Certification: ask for a TUV or SGS mark on the cylinder body. A cylinder is the one component in a chair that can fail violently rather than gradually.
• Finish: chrome-plated cylinders show fingerprints and salt damage on a terrace; black nitride holds up about three times longer outdoors.

Seat plate thickness and mounting

The plate is cheap, and it is the part that makes a chair repairable rather than disposable.

• 2.0 mm: adequate for a lounge chair used a few hours a day. It flexes visibly above about 110 kg.
• 3.0 mm: USD 1.10 to 1.90 more per chair, and required above a 130 kg specified load or with any synchro tilt, because the spring reaction loads the plate in bending.
• Bolt pattern: mounting holes vary 3 to 5 mm between mechanism suppliers, so a replacement has to be matched to the original plate, not to a chair model name.
• Fixing: four M6 bolts into welded nutserts at 8 to 10 Nm, re-checked at 7 and 30 days in service.
• Welded plate: on a metal-framed chair the plate can be welded instead of bolted, which removes the loosening failure altogether and adds USD 0.90 to 1.60.

The four tilt types

Recline is specified in degrees and in lock positions, and the two numbers together decide comfort across a long sitting.

• Fixed swivel: no recline at all. Hotel lobbies and waiting areas, where a fixed back is one less thing to break.
• Centre tilt: 8 to 12 degrees from a pivot under the seat centre, with a single upright lock.
• Knee tilt: 12 to 18 degrees with the pivot forward of centre, so the seat front rises less. Better below a 460 mm seat height.
• Synchro: 18 to 22 degrees with the seat and back moving in a roughly 2 to 1 ratio, and 4 or 5 lock positions.
• Tension: the spring adjusts across about 45 to 130 kg. Set it for the lightest user, not the heaviest, or the lightest user cannot recline at all.
• Tip-over: anything past 20 degrees of recline needs a base footprint check, because the centre of mass moves back 60 to 80 mm at full recline.

Cycle testing, and what fails first

Two laboratory numbers matter, and one number from the field is the one that sets the spares budget.

• Laboratory: backrest durability to 120,000 cycles and swivel to 120,000 revolutions under BIFMA X5.1. EN 1335 and EN 12520 set lower figures for domestic seating, which is why a domestic-rated chair does not belong in a lobby.
• Our bench: three sample mechanisms per batch run 25,000 recline cycles at 100 kg, and the cylinder is held at full extension for 72 hours to catch slow seal creep.
• Failure order in the field: gas lift seal at 3 to 5 years, tilt tension spring at 4 to 6 years, castor bearings at 2 to 4 years, seat plate welds almost never.
• The symptom: a chair that sinks 10 to 25 mm overnight has a failing cylinder seal. That is a replacement, not an adjustment.
• Claim rate: 1.2 to 2.4 per cent per year across a mixed lounge and lobby fleet, almost all of it cylinders and castors.

Ordering spares and writing the spec

Mechanisms are the one category where we push buyers to order spares with the chairs, because the unit is a stock item for us and a long wait for you.

• Allocation: 1 per cent of the order quantity in gas cylinders and 0.5 per cent in tilt units, packed loose in one marked carton per container.
• Unit prices: gas cylinder USD 9 to 22 by class, tilt unit USD 18 to 45, a set of five castors USD 4 to 11.
• Swap time: a cylinder takes 15 to 20 minutes with a puller and a mallet, a tilt unit 25 to 35 minutes with the chair inverted on a bench.
• Specify: cylinder class and stroke, cycle rating, plate thickness in mm, tilt type and number of lock positions, castor material and diameter.
• Avoid: "mechanism to match sample". It leaves the class, the stroke and the cycle rating all open.

The lounge and lobby frames we build these units into are shown on the lounge and lobby chairs, and the spares pack issued with a project order is described on the OEM spares programme.