Gas spring

A gas spring consists of a sealed cylinder filled with a charge of high-pressure{{Cite book |title=Pneumatic Handbook |url=https://www.sciencedirect.com/book/9781856172493/pneumatic-handbook |access-date=2024-09-12 |isbn=978-1-85617-249-3 |language=en |last1=Barber |first1=Antony |date=1997 |publisher=Elsevier Science }} gas, a piston rod attached to a piston with a sliding seal, and some oil. The piston (or the cylinder wall) contains a number of channels that allow the gas to transfer between the lower chamber (between the piston and the closed end of the cylinder) and the upper chamber (between the piston and the head cap). This causes the pressure in both chambers to equilibrate no matter how far the piston is pushed down the tube.

In the ideal case of a piston moving with zero friction through a fully sealed cylinder, there are two key phenomena which can be thought of as acting simultaneously inside the spring as it is compressed.{{Cite web |title=Technology and characteristics of gas springs |url=https://www.vapsint.com/en/technology-and-characteristics-of-gas-springs/ |access-date=2024-10-19 |website=Vapsint}} Firstly, as the spring is compressed and the piston rod is pushed into the cylinder, the effective volume of the cylinder decreases due to the extra space now being occupied by the solid piston rod.{{Cite web |title=Technology and characteristics of gas springs |url=https://www.vapsint.com/en/technology-and-characteristics-of-gas-springs/ |access-date=2024-09-16 |website=Vapsint}} This would be the case even if there were no piston attached to the rod, as the only changing factor is the cylindrical volume of the rod itself. Second, the bottom of the piston always experiences a greater force opposite to the compressing action than the top. Even though the compressed gas exerts an equal amount of force on all the inner surfaces of the cylinder and piston rod, the force contribution in the direction of travel is practically zero for the sides of the rod, but nearly total for the bottom of the rod. The addition of a piston to the end of the rod thus does not alter the net forces involved,{{Citation needed|date=September 2024}} but instead partially separates the cylinder into two volumes with restricted flow of gas and oil{{Cite web |title=Technology and characteristics of gas springs |url=https://www.vapsint.com/en/technology-and-characteristics-of-gas-springs/ |access-date=2024-10-19 |website=Vapsint}} between them, through flow-restriction channels in either the piston or the cylinder wall.

Gas springs whose pistons have fine holes in them for damping are called slow-damper springs and are common on safety gates and doors.

According to Hooke's law, If the internal plunger features a diaphragm that extends to the side of the gas tube, it will stop moving once the applied force becomes constant and will support a weight, like a normal spring.{{Cite web |last= |first= |date=2024-05-06 |title=Does Weight Affect Spring? |url=https://www.tevema.com/does-weight-affect-spring/#:~:text=Weight%20can%20indeed%20affect%20the,on%20the%20type%20of%20spring. |access-date=2024-10-19 |website=Technische veren specialist {{!}} Tevema.com |language=en-US}} Some gas springs have fine holes in the plunger for additional damping:{{Cite web |last=Rowland |first=David |date=2019-04-29 |title=A Guide to Gas Spring Design and Customization |url=https://www.machinedesign.com/mechanical-motion-systems/article/21837752/a-guide-to-gas-spring-design-and-customization |access-date=2024-10-19 |website=Machine Design |language=en}} these are called "slow-damper springs" and are common on safety gates and doors. A gas spring designed for fast operation(s) is termed a "quick gas spring" and is used in the manufacture of air guns and recoil buffers.{{Cite web |title=6 Types of Air Rifles for Air Gun Hunting {{!}} Crosman |url=https://discover.crosman.com/blog/6-different-types-air-rifles-airgun-hunting#:~:text=Advantages:%20The%20Nitro%20Piston%C2%AE,in%20a%20cylinder%20is%20compressed. |access-date=2024-10-19 |website=discover.crosman.com |language=en}}

It is possible to reduce the gas volume and increase its internal pressure by means of a movable end stop, or by allowing one tube to slide over another, allowing the characteristics of a gas spring to be adjusted during operation. The rod may be hollow by use of clever seals, or it may consist of multiple small-diameter rods. A small amount of oil is normally present.{{Cite web |title=Technology and characteristics of gas springs |url=https://www.vapsint.com/en/technology-and-characteristics-of-gas-springs/#:~:text=and%20so%20on.-,Braking%20action,(Dynamic%20Damping%20Gas%20Spring). |access-date=2024-10-19 |website=Vapsint}}

The gas may be introduced by a Schrader-type valve, using a lip seal around the rod and forcing it to allow gas in by external overpressure or a shuttling O-ring system. Gas springs with high caliber contain a very large amount of energy, and can be used as a power pack. In emergency use, the gas may be introduced via a gas generator cell, similar to those used in airbags.{{Cite web |last=Merola |first=Joseph |date=1999-10-25 |title=How do air bags work? |url=https://www.scientificamerican.com/article/how-do-air-bags-work/ |access-date=2024-10-19 |website=Scientific American |language=en}}

A gas spring can be given adjustable push-in force via a local knob or remote via a Bowden wire.{{Cite web |last=Babinec |first=Brice |date=2023-02-07 |title=Understanding Bowden Tubes and Feed Tubes |url=https://www.mlc-cad.com/understanding-bowden-tubes-and-feed-tubes/#:~:text=What%20is%20a%20Bowden%20Tube?&text=These%20tubes%20serve%20somewhat%20of,advantage%20of%20a%20Bowden%20system. |access-date=2024-10-19 |website=MLC CAD Systems |language=en-US}}

Extended stroke is usually acquired through telescoping mechanisms, composed of one rod and multiple cylinders, where the smaller of the two cylinders actually acts as a second rod extending in and out of the larger cylinder.

There are also techniques to make variable-lift gas springs. These are intended for short production runs and prototypes, and in applications where the exact force is important but hard to estimate in advance, such as lifting a lid slowly in a known time. In this case, the cylinder is supplied filled to maximum design pressure but equipped with a bleed port to allow gas to be released once installed. The intention is that the design can be over-sprung, and then the pressure is reduced in stages to optimize behavior. If too much gas is released, a new spring must be installed.{{Cite web |last=hosting |first=Spinning Planet-Professional Web Design & |title=Everything You Need to Know About Gas Struts |url=https://www.comac.co.nz/blog/everything-you-need-to-know-about-gas-struts#:~:text=If%20too%20much%20gas%20has,Mac%20to%20be%20re-gassed. |access-date=2024-10-19 |website=Co-Mac |language=en}}

It is also possible to make degressive gas springs, where the spring becomes more, not less, powerful as the main cylinder expands.{{Cite web|url=https://patents.google.com/patent/US5833218|title=Degressive gas spring}}

Gas springs are often used in office chairs, truck tailgates, and wheelchairs, just to name a few. A rare concern with gas springs is that if it is made cheaply, using oxygen as its internal gas, the oxygen will combust given enough force. This is because oxygen is a combustible gas{{Cite web |last=Dillon |first=Stephanie |title=The Chemistry of Combustion |url=https://www.chem.fsu.edu/chemlab/chm1020c/Lecture%207/01.php#:~:text=What%20is%20Combustion?,it%20just%20burst%20into%20flames? |access-date=2024-10-19 |website=www.chem.fsu.edu}} and nitrogen is not.{{Cite web |last= |date=2023-12-29 |title=What Type of Gas Do Gas Springs Use? |url=https://monroeengineering.com/blog/what-type-of-gas-do-gas-springs-use/ |access-date=2024-10-19 |website=OneMonroe |language=en-US}} Oxygen is not flammable itself however, it does oxidize the internal parts in high heat. The internal parts of the gas spring, in great tension and heat, then explodes with the oil and grease within the gas spring.{{cn|date=October 2024}} A reported incident in 2008 involved an elderly man who suffered severe injuries due to a 150mm rod forcefully ejected from the explosion.{{Cite web |date=2023-09-18 |title=Office Chair Explosion Incidents: Causes and Solutions |url=https://vaseat.com/office-chair-explosion-causes-and-solutions/#catlog0 |access-date=2024-10-19 |website=Vaseat Furniture}}

There are a few common signs of failure for gas springs. To list a few: Leakage of gasses, failure to support its weight compacity, unusual noises, excessive bouncing, and sagging.{{Cite web |title=Warning Signals of a Failing Gas Lift Springs In Suspension Systems |url=https://www.zhiligasspring.com/news/warning-signals-of-a-failing-gas-lift-springs-in-suspension-systems.html |access-date=2024-10-19 |website=Zhili Gas Spring |language=en}}

• Shock absorber

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Category:Springs (mechanical)