Cabinet Flap Falling Shut? How to Retrofit a Stronger Gas Strut (e.g. 150 N)

A gas strut keeps upward-opening cabinet flaps securely in position using compressed nitrogen gas; if the flap falls shut by itself, the spring force in Newtons (N) is insufficient for the weight of the flap.

When an overhead cabinet door in a kitchen or living room fails to stay open, it is generally due to pressure loss within the strut cylinder or an incorrectly calculated load rating from the start. For joiners and fitters, the task involves replacing the defective component with an exact matching fitting. However, upgrading to a stronger gas strut – for instance, opting for 150 N instead of the factory-fitted 80 N – requires a precise check of dimensions, leverage ratios, and existing hinges.

This guide outlines the technical parameters required to identify the correct replacement for failing flap fittings and install them professionally.

Why Cabinet Flaps Fall Shut: Causes and Mechanics

A gas strut consists of a cylinder and a piston rod. The cylinder acts like a sealed chamber where the piston moves against the resistance of enclosed gas. Each time the flap is closed, the rod retracts into the cylinder, compressing the gas. Upon opening, the gas pushes the rod back out, assisting the lifting motion.

Over the years, if the seal loses its integrity, gas slowly escapes. As a result, the holding force falls below the weight of the flap. Another frequent cause for falling doors is a subsequent change in weight – such as replacing a lightweight chipboard front with heavier MDF or even solid wood. In both scenarios, a strut with a higher nominal force rating must be retrofitted.

Key Buying Criteria for Gas Struts

Selecting the correct hardware depends strictly on physical and geometrical factors. Aesthetics are secondary, meaning selection focuses entirely on functional parameters.

1. Spring Force in Newtons (N)

The strength of the strut is specified in Newtons. As a rough practical guide, 10 N corresponds to a lifting force of approximately 1 kg under direct vertical load. However, because a cabinet flap involves leverage, the required force must be higher than the pure weight of the front panel. Typical increments in furniture construction include:

• 50 N / 60 N (for very small, lightweight flaps)
• 80 N / 100 N (standard size for regular kitchen overhead units)
• 120 N / 150 N (for large or heavy fronts)

2. Installed Length and Stroke

The total length of the strut is measured when fully extended, from the centre of one ball socket (eye) to the centre of the opposite ball socket. A standard measurement for typical kitchen flaps is 268 mm. The stroke defines the travel distance that the piston rod can retract into the cylinder – usually around 90 mm. If the installed length does not match the original, the opening angle of the flap will change drastically, or the door will no longer close fully.

3. Mounting System and Brackets

Most struts are mounted using a ball joint clip system. The ball stud typically has a diameter of 10 mm. The mounting brackets screwed to the carcase and the door frequently follow the standardised System 32 (32 mm hole spacing), which makes replacing worn components significantly quicker.

Calculating the Correct Spring Force

To prevent the flap from falling shut again or, conversely, becoming too stiff to close, the force rating must be precisely matched to the door panel.

The calculation requires the weight of the flap (including the handle) and the height of the flap. A simplified rule of thumb for fitters is: Flap weight in kg × flap height in mm ÷ 100 = required force in kg. Multiply this result by 10 to obtain the value in Newtons.

Example: A flap weighs 4 kg and is 400 mm high. 4 kg × 400 mm = 1600. 1600 ÷ 100 = 16 kg of leverage force. 16 kg × 10 = 160 N.

Because two struts should always be fitted per flap to prevent warping, divide the 160 N by two. In this case, two struts rated at 80 N each are required. If the flap were made of heavy timber weighing 7 kg, the total requirement would be around 280 N. Here, selecting two 150 N struts would be appropriate. For exceptionally heavy fronts, specialised Gas Struts for Heavy Flaps are available.

Overview of Types and Options

Different fittings are used depending on cabinet design and opening mechanics. It is essential not to confuse the systems.

• Standard gas struts: Push the flap upwards and hold it open. They are available in various N ratings and in different finishes to match cabinet interiors, including Gas Struts Silver, Gas Struts Black, or Gas Struts White.
• Mechanical flap stays: Function without gas pressure, relying instead on friction. The holding force is usually adjusted manually via an Allen key. See the Flap Stays category for these options.
• Braking flap stays (drop-down fittings): When a flap opens downwards rather than upwards (such as in a drinks cabinet), upward-pushing gas struts must not be used. In these cases, dedicated Flap Fittings designed to decelerate the falling door are required.

Which Strut for Which Application? (Selection Guide)

• If you are repairing a standard kitchen flap (height approx. 300 mm - 400 mm, melamine-faced), then choose two Gas Struts rated at 60 N or 80 N each.
• If the front incorporates a glass panel or is wider than 800 mm, then opt for stronger models rated at 100 N or 120 N.
• If a very large flap is installed (e.g. above a microwave) made of solid material, then using two struts rated at 150 N each is essential.
• If the flap slams loudly against the carcase when closing, then you do not need a weaker strut; instead, fit additional Buffers & Dampers or drill-in door stops on the carcase edge.

Installation Guide: How to Retrofit Gas Struts Correctly

Replacing a defective strut takes only a few minutes, provided the replacement fittings have the same installed length.

Required Tools:

• Pozi screwdriver (size PZ2)
• Flat-blade screwdriver (for releasing the retaining clip)
• Tape measure
• Bradawl if required (if new pilot holes must be marked)

Step-by-step Instructions:

1. Removal: Open the flap fully and have a second person support it. Slide the flat-blade screwdriver under the small metal spring clip at the ball head of the old strut and lift it gently. The strut can now be pulled off the ball stud.
2. Checking the brackets: Measure the diameter of the remaining ball stud. If it measures 10 mm, the existing mounting brackets can often remain screwed into the carcase.
3. Replacing mounting brackets (if necessary): If the ball heads do not match, unscrew the old brackets. Fasten the new brackets using chipboard screws (typically 3.5 x 16 mm). Maintain the correct edge distance (commonly 37 mm under System 32).
4. Clipping into place: Press the new strut firmly onto the ball studs until the metal clip audibly clicks into position.
5. Correct orientation: Install the strut so that the thicker cylinder is attached to the carcase and the thinner piston rod is attached to the flap. This orientation ensures internal lubricants keep the seal at the rod exit properly lubricated.

Important: Gas struts do not replace hinges. The flap must still be held securely by intact hinges at the top panel. Struts perform best when combined with Concealed Hinges / Cabinet Hinges with Soft Close.

Frequently Asked Questions (FAQ)

Can I simply replace an 80 N strut with a 150 N strut? No, unless the flap was significantly too heavy for the 80 N rating in the first place. If you fit 150 N struts to a lightweight door, the opening force will be too high, making the flap difficult to pull shut. Furthermore, the excess force can tear hinges or mounting brackets out of the chipboard.

Why do I need two gas struts per flap? If only one strut is fitted on one side, the lifting force acts asymmetrically across the panel. Over time, this causes the door to twist and places excessive strain on the opposite hinge. Always install two struts of identical strength.

How do I measure the length of a strut correctly? Measure the strut when it is fully extended. The dimension is taken from the centre of one mounting eyelet (ball socket) to the centre of the other.

What is the difference between a gas strut and a door damper? A gas strut actively pushes a flap upwards and keeps it open against gravity. A door damper (often called soft-close) has no lifting capability. It merely slows down the momentum of a closing door over the final few centimetres. To stop doors banging shut, you need Door Dampers or Drawer Runners with Soft Close.

Can a gas strut be repaired or regassed? No. The cylinders are under high pressure and are factory-sealed. Opening them is dangerous and not intended for furniture hardware. A worn strut must be replaced completely.