A Guide to Gas Spring Design and Selection

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Why engineer the selection?
How a gas spring works
Common types
Selection factors
Typical industry requirements
From selection to production: cylinder machines
Reference
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Why engineer the selection?

Ordering a standard gas spring from a catalogue looks convenient, but it often leads to the wrong force, not enough installation space or the wrong end fittings. Engineering the selection takes more effort up front, but the gas spring works correctly the first time and you avoid repeated trial and error.

Cylinder tubes after inner grooving

Gas spring with end fittings

Closed gas spring cylinders

How a gas spring works

A gas spring is a self-contained, maintenance-free force cylinder. The cylinder is filled with pressurized nitrogen, which pushes on the piston to produce output force. When the rod is compressed, nitrogen is metered through an orifice, which controls the speed.

Mounted rod-down, a small amount of oil in the cylinder cushions the end of the stroke. Some gas springs have a field-adjustable bleed valve to release nitrogen and reduce force.

Common types

Push type

The most common type, used to lift and lower loads easily. Internal pressure pushes the rod out; widely used to support lids and doors.

Pull type

Compact and mountable in any orientation. The opposite of a push type: cylinder pressure pulls the rod in. Progression can be as low as about 11%.

Locking type

Locks anywhere in the stroke. Pressing a button opens the piston valve; release it at the desired position and the rod locks. Common in office chairs, medical equipment and special devices.

Selection factors

Load weight and mounting angle
Required force range
Stroke and extended length
Installation space and end fitting type
Operating temperature
Whether locking is needed
Damping and cushioning requirements

Q: Standard or custom?
Standard gas springs usually come in only a few force ratings and suit simple applications. If your installation space, force or damping is special, give the real conditions to the manufacturer for an engineered selection.

Q: What is progression?
Progression is how much the force rises over the stroke. A standard push-type gas spring has about 30% progression, meaning the fully compressed force is about 30% higher than the extended force. Pull types can be as low as about 11%, giving a flatter force curve.

Typical industry requirements

Shock absorbers: precise damping and stroke control, higher forces
Furniture: lower forces but long life, often with locking
Strollers: lightweight design and strict safety approvals
Automotive: tailgate and bonnet force calculated from weight and opening angle
Industrial equipment: guards and maintenance doors, with oil and temperature in mind
Medical: stainless steel, high reliability, hygiene approvals

From selection to production: cylinder machines

Once the gas spring is specified, the cylinder has to be produced: cutting, roll grooving, end closing, inner oil grooves, oil filling, press-fit & edge folding and end fitting. TONG DA Precision (Tainan, Taiwan, since 1989) designs and builds these machines and can plan a single machine or a complete line around your cylinder size and stroke. See How are gas springs made? for the machine at each step. For quotations, email sales@tdco.com.tw.