Choosing PTL Gas Springs for Terrace Wind Screens

Increasingly common on café and restaurant terraces, the "piston wind screen" is a glass barrier that disappears when lowered and rises to block the wind when needed. The mechanism at its heart is not an ordinary gas spring but a PTL (push-to-lock) locking gas spring. Getting it right comes down to selecting a single value correctly — the force.

How PTL works: tap to raise, push to lock

PTL is a two-position system, like a click pen. With the panel down, the gas spring is locked and the glass stays put on its own. When the user applies a light force to the panel, the lock releases; because the spring force exceeds the panel weight, the glass rises on its own to the end of stroke (top stop). To close, the user pushes the panel down, and when the glass reaches the bottom the PTL locks again. No crank, no motor, no electricity — one touch.

Force selection: strong enough to lift, light enough to close

Here the usual sizing logic is inverted. In a normal gas spring you pick a force that balances the lid; in a PTL wind screen the force must be high enough to safely overcome the panel weight and carry it to the top stop — otherwise the glass stalls halfway. Yet that same force must be low enough for a person to push the panel back down and close it. This sweet spot between two extremes is the essence of the selection:

• Force too high: the panel shoots up, impacts the top stop, and is hard to push down when closing.
• Force too low: the panel cannot fully open and hangs at half height.

Give the glass weight (panel + frame) and the number of springs clearly; we set the force against both extremes together. On wide panels, using two springs both splits the load and balances the motion.

End of stroke: damping inside the spring

Because the panel rises on its own, it approaches the top stop at speed; on heavy glass an uncontrolled impact is both noisy and fatiguing for the glass and its fittings. The solution is inside the gas spring: as it nears the end of stroke, a damping (braking) phase engages, slows the panel and settles the glass gently onto the top stop. Because the impact is absorbed by the gas spring, the mechanical stop merely sets the final limit rather than taking the blow on every cycle — which extends the life of the connection.

Outdoor use: stainless and force loss in the cold

A wind screen is outdoors every day of the year, with two consequences. First, corrosion: for rain, humidity and coastal salt exposure a stainless (inox) body and rod markedly extends life — and the fittings must resist corrosion at least as well as the spring. Second, temperature: nitrogen pressure changes with temperature, roughly 3.3% of force per 10 °C. A panel that opens fully at 30 °C in summer may stall halfway at −10 °C in winter. Verify the force against the coldest working temperature of the year.

Safety

A heavy pane that rises on its own puts safety first in the design: a geometry that will not pinch fingers, a controlled opening speed, and a solid track/guide so the panel cannot tip. Because PTL provides a positive lock in the closed position, the panel will not open by itself in the wind — the system's greatest strength — but its secure hold in the open position must be confirmed by a separate mechanical stop.

COMSTAN manufactures application-specific gas springs — including PTL locking and stainless options — for piston wind screen and rising glass barrier makers. Send us your glass weight, panel size and working temperature, and we will work out the force and quantity recipe together.