Diagnosis
Sinking does not prove which component failed.
HON’s current support guidance states that a chair that sinks or will not raise/lower can be caused by either the control mechanism or the pneumatic cylinder. That is a useful general rule: diagnose the actuation/control side before assuming the sealed gas spring itself is the only candidate.
- Check whether the height lever moves freely and actually engages the mechanism.
- Look for visible damage or looseness where the control mechanism meets the cylinder.
- Record the model and serial number before ordering anything.
Part selection
Do not select a replacement from a generic weight-class chart.
Marketplace listings often advertise “Class 3” and “Class 4” cylinders with broad weight ranges. Those labels do not replace the chair manufacturer’s own occupant rating, cylinder dimensions, control geometry, or approved replacement part. BIFMA chair standards test the complete chair; they are not a universal lookup table that turns a gas-spring class into a safe occupant weight for every chair.
Use the exact chair model, serial number, seat-height range, base/control fit, and manufacturer part number where available.
Replacement
Use the procedure for the chair you actually own.
Removal methods vary. Steelcase, for example, publishes a Gesture cylinder procedure that uses a specific pneumatic-cylinder removal tool and hammer. Other manufacturers may direct owners to a dealer or qualified service person. Follow that model-specific procedure rather than assuming a pipe wrench and mallet are appropriate for every chair.
Decision
Do you need a cylinder?
If the manufacturer diagnosis points to the control mechanism, replace/service that part instead.
If the exact chair documentation identifies the cylinder and a supported replacement is available, use that part and procedure.
If the chair is under warranty, uses an undocumented/proprietary mechanism, or the cylinder is seized/damaged, contact the manufacturer or dealer before escalating force.
Sources