http://www.balajiengineering.com/technical-info.html

What is Gas Spring? How it works?
As the name implies, the product is Nitrogen gas filled and performs like a compression spring. The spring consists of a piston rod attached to a piston and valve assembly moving within a sealed cylinder containing nitrogen gas at a certain predetermined pressure. The output force is the result of the differential force along the piston due to area difference. Compression type gas spring act like a standard metallic coil spring with lots of added advantages, like smooth opening and closing operation, almost flat curve characteristic, easy mounting and less maintains, flexibility in design, long life, high starting force, less force transferred on mounting hinges and compact design, to name a few of them.


The small quantity of oil incorporated in the cylinder provides extra cushioning at the end of the stroke thereby reducing the end jerk and load on the hinges.
 
These gas springs are available in two major types, non lockable and lockable.

Non lockable gas springs ( Gasolift ) are in extended condition when not loaded. These are mainly used in easy lifting and lowering of equipment. Intermediate positive locking along the stroke is not possible.

Lockable gas springs ( Gasoblock and Gasohite ) can be positively locked in any position along the length of the stroke. A valve mechanism is incorporated which effects in locking condition at any position along the stroke of the gas spring.

Gasoblock gas springs are having a valve in the piston rod and can be operated by a valve actuating mechanism through the piston rod. In this type of gas spring there are three different types, mainly spring blocking, rigid blocking in extension and rigid blocking in compression. These are mainly used in passenger seats, hospital furniture and office chairs.

Gasohite gas springs are having a valve in the tube assembly and can be operated from the top of the cylinder. These are mainly used for variety of chairs for height adjustment and revolving.
 
 
Operating Temperature Range
The gas springs are designed and manufactured to withstand continuous temperature of -20 degree centigrade to +80 degree centigrade. An exposure to 100 degree for a period of half an hour continuous is permissible.

BALAJI can supply gas springs for lower and higher temperatures than specified on special request. The range is from -40 to + 120 degree centigrade.
 
 
Installation Instructions
The gas springs should be mounted with piston rod in down condition so as to ensure seal is dipped in oil during maximum of its working life. For rigid lockable gas springs, they can be mounted in any position.
Avoid paint, welding spatters, thinner, dust etc. on the piston rod. Preferably gas spring should be mounted lastly during assembly.
Avoid or minimize side loading on the piston rod.
Ensure that the mounting pins in the eyelet type end mounting are free enough and well lubricated to avoid side loading on rod during operation.
Ensure that the ball pins for the ball joint type mounting are properly tightened in the bracket to avoid loose pin and play.
Do not heat or open the gas springs.
For Gasohite gas springs, ensure proper taper fitment of mating top and bottom parts of the chair to avoid play and side loading.
For Gasoblock and Gasohite gas springs, ensure that the valve actuator is not pre loaded and a gap of minimum 1 mm exists between valve actuator and the actuating lever.
Dispose the gas springs as per the manufacturer's instructions only.
 
Material Safety
Balaji cares for the Environment. Gas spring should be disposed off as per the following procedure.

 

Leak the high pressure gas by drilling a hole at 2mm diameter in tube. Ensure to leak the gas from both the component of springs.
Ensure that the piston rod is freely moving in the tube.
Open the gas spring by machining between the ends on turning centre.
Remove all the parts and clean thoroughly
The metallic (Steel) part can be scrapped by damaging the same to avoid misuse.
The plastic parts can be delivered for recycling.
The rubber parts and oil should be destroyed as per the local municipal regulations.
 
Advantages of Gas Springs
Smooth opening and closing operation :
The unique design of piston and valve assembly and nitrogen gas, provides damped extension or smooth and effortless opening and no damping or easy closing of any cover or lid. The small quantity of oil incorporated in the cylinder ensures proper lubrication to seal and in addition the damping effect at the end of the stroke. This cushioning at the end of the stroke provides jerk less opening.
Almost flat curve characteristic :
Unlike coil spring, the gas spring exhibits the high force right from the beginning of the stroke. It means there is no necessity to compress the spring to get required force, like a coil spring. The force versus stroke curve is almost flat. Please refer following graph. This unique feature of gas spring made the application engineer's job very easy.
Easy mounting

https://www.explainthatstuff.com/gassprings.html

Gas springs
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by Chris Woodford. Last updated: December 3, 2020.

Have you ever tried lifting the trunk lid (sometimes called tailgate, hatch, or boot) of your car with just one finger? How come you can lift a heavy piece of metal and glass with so little force? The answer, if you didn't know already, lies in those clever piston-like hinges that support the lid either side. They're called gas springs (or gas dampers) and they make our lives a whole lot easier in all sorts of ways.

If you're sitting on an office chair right now, there's probably a gas spring underneath your body. Release the height lever and you'll feel (and probably hear) the gas in the spring being compressed as the seat gently falls down. Gas springs have loads of other uses too. Let's take a closer look at these handy gadgets and find out how they work!

Photo: A sturdy gas spring (the thin black cylinder and the silver rod that slides in and out) supports the tailgate of this car during loading and unloading. It looks a bit like a bicycle pump, but it works in a very different way.

Contents
Why do we need gas springs?
How a gas spring works
How a gas spring generates a force
Gas springs as dampers
Gas springs as energy reservoirs
How a gas spring stores and releases energy
How does the gas stay inside?
Why use a gas spring?
Find out more
Why do we need gas springs?
Office chair with gas spring lift

Photo: A vertically mounted gas spring supports the seat of this "gas-lift" office chair, making it easy to adjust the height. Gas springs generally work best in a vertical position like this. There's less chance of them buckling when fully extended and the oil inside lubricates them more smoothly and evenly.

Suppose there were no springs on the hatchback of your car. It would be really heavy to lift, for one thing. Awkward too, given its length. There'd be nothing to hold it up in the air when you wanted to load in your shopping, which would be a real nuisance. You'd have to pin it open with a clumsy metal support, like you do with the hood (bonnet), which would probably be all dirty and oily. If you let the lid go, it would crash down onto your car's bodywork, probably doing a lot of damage in the process.

Saloon cars with small trunk lids often use normal metal springs, but those are not a great solution for hatchbacks, liftbacks, and similar cars. A simple "tension" spring (one that you have to work to pull apart) would need to be very stiff and heavy, so it would take a huge amount of effort to lift the hatch high in the air. The higher you lifted it, the harder it would get to lift any further. With the lid opened up fully, the spring would be stretched out so much that it would pull straight back down again. You could use a "compression" spring instead (one you have to work to push together), but it's often better to use an entirely different kind of spring: one that doesn't rely on stretching or squeezing metal to absorb energy.

How a gas spring works
The basic idea
A gas spring is a bit like a super-sturdy version of a bicycle pump, only it's filled with pressurized nitrogen gas (the major constituent of the air around us) and oil and completely sealed up so they can't escape. The gas allows the spring to store energy, while the oil damps (slows and smooths) the movement of the piston and also provides lubrication. Just like in a bicycle pump, there's a tight-fitting piston mounted on a rod that can slide back and forth inside a cylinder (made from heavy gauge steel, not light plastic as in a bicycle pump).

Push on a gas spring and you force the piston rod and piston into the cylinder and this compresses the gas. Stop pressing and let go and the pressure of the gas pushes the piston back out again. So far, that sounds just like a bicycle pump—but it's working in a different way. Unlike with a bicycle pump, gas inside the cylinder can actually flow through or around the piston from one side to the other as it moves back and forward. Exactly how this happens varies from one design of gas spring to another; usually the piston has one or more holes or valves in it. Now if the piston can move through the gas, you might think it isn't compressing the gas at all. But don't forget that the whole cylinder is completely sealed. When the piston rod is inside the cylinder, it's taking up room that the gas previously occupied. In other words, when a gas spring is fully pushed in, you've compressed the gas inside by an amount equal to the volume of the piston rod. If the piston rod occupies virtually the whole cylinder, you can see that the gas is getting compressed quite substantially. The gas pressure can be very high, typically up to about 170 times normal atmospheric pressure!

Animation showing how a gas spring compresses the nitrogen gas inside.

Photo: The gas inside a gas spring can flow through or around the piston from one side to the other, but it can't escape from the cylinder. The whole system

https://www.machinedesign.com/mechanical-motion-systems/article/21837752/a-guide-to-gas-spring-design-and-customization

A Guide to Gas Spring Design and Customization

pril 30, 2019
Knowing how gas springs work will help you select the right one for a design.
David Rowland
When a design calls for an industrial gas spring, there’s a wide range of standard, off-the-shelf products available from various manufacturers. But ordering a gas spring from a catalog comes with a lot of risks. Depending on the application, it’s likely that some degree of customization is necessary to ensure just the right gas spring is found.

There is a better way to get the best gas spring: Take an engineering approach to adding gas springs to designs, and use standard industrial gas springs as a starting point.

Machinedesign Com Sites Machinedesign com Files G1 Image

Gas springs are self-contained, force generating, maintenance-free cylinders. They are used to move and position lids, chairs, table-tops, and host of other assemblies. body is pre-charged with nitrogen gas to provide a specific output force. Pressure is applied to the piston and diameter area, which provides the output force in push-type gas springs.

Standard Gas Springs
Standard gas springs are quick and easy to order. They’re also relatively inexpensive, provided they don’t need troubleshooting right out of the box to fit the application. However, customers may underestimate how much data they need to specify gas springs. Furthermore, off-the-shelf gas springs commonly offer only one of three choices of output force. Will one of them be exactly right? There’s a good chance designers and customers may get unintended results.

If factory-supplied output forces don’t work, hoods or lids may open unexpectedly, or the spring might not support the load it needs to move. Another concern with off-the-shelf gas springs: customer drawings fail to allow room in the installation for the spring. Or, the spring comes with the wrong end fittings. These situations often force customers to waste time trying different forces and modifying the assembly, and they still may not get the right gas spring for the job. All this trial-and-error inflates labor costs and the project suffers needless delays.

Unlike most standard gas springs, an engineered spring is, in essence, a custom part the manufacturer typically adjusts to an application’s specifications. The added investment usually pays off via saved time and labor costs that come from gas springs working perfectly the first time.

Machinedesign Com Sites Machinedesign com Files G2 Steel Cutaway

Gas Spring Basics
To understand the important factors to consider when ordering a custom gas spring, engineers should know the basics behind how they work.

Gas springs are self-contained, force generating, maintenance-free cylinders. The body is filled with pressurized nitrogen gas that generates a specific pressure. The pressure pushes on the piston, which provides the output force in push-type gas springs. As the piston rod is pushed and compressed, the piston generates a constant output force and controls its velocity by metering nitrogen through a hole. A little oil dampens, or cushions, piston movement at the end of travel when the gas spring is mounted with the piston rod facing downward. Some gas springs have a field-accessible vent valve for venting nitrogen to reduce the spring’s force.

Depending on the application, designers can choose from several types of gas springs. Some common gas spring types include:

Push-type to lift and lower loads with easy control and minimal exertion. Push-type gas springs support covers and lids in a broad range of industries.

Pull-type to fit in tight. This type is compact and mounts in any orientation and position. Unlike in standard push-type springs, pressure in the cylinder retracts the piston rod. Pull-types can have low progression rate. Progression is the increase in force exerted by the gas spring over the stroke. Progression rates, which measure the change in progression, can be as low as 11%.

They also can have an adjustment valve to control the traction force. Traction force is the pulling force from the gas pressure that retracts the rod. It can be as low as 11 lb and as high as 1,630 lb, depending on the gas spring. Providing this pulling force is the gas spring’s main function as it helps in lifting and holding up all types of heavy objects in many different applications.

Locking to hold a position. Chairs often need to maintain a certain position to support a patient or someone. In an adjustable desk chair, for example, a person adjusts the height by first pressing a button or lever. This opens a piston valve so the seat can be moved up or down to the desired position. Letting go of the button or lever lets the valve closes and locks the piston so the seat remains at that height.

Two custom-made stainless-steel locking gas springs from Ace Controls lets this hygiene and toileting device for children with disabilities be inclined up to 15 deg. forward or aft and be easy to clean.

Machinedesign Com Sites Machinedesign com Files G3 Image

https://www.gasspringindia.com/

Lockable Gas Springs ( Ideal - Block )

Lockable gas springs have the mechanism that enables the piston rod to be locked at any position in its stroke. This mechanism is triggered by a plunger that is linked with the rod. When this plunger is pressed the rod becomes free to operate as compression gas springs. When plunger is released at any point in the stroke, the rod is locked in that position.
The Internal Design of the lockable gas springs consist of components such as piston rod, piston valve, cylinders, guides, seals etc. Inside Pressure is generated by gas(nitrogen) and oil inside the cylinder. These Gas Springs are applicable for Lockable Gas Springs, Gas Spring For Hospital Beds, Hospital Furniture, Dentist Chairs, Operation Tables, Labour Tables, Emergency Casualty Trolleys, Passenger Seats, Wheel Chairs.

Lockable Gas Springs
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Lockable Gas Springs
Lockable Gas Springs
Application

Lockable Gas Spring For Hospital Beds
Lockable Gas Spring For Hospital Beds


Hospital Furniture - Examination Couch Back Rest
Hospital Furniture - Examination Couch Back Rest


Hospital Furniture - Overbed Tables
Hospital Furniture - Overbed Tables


Hospital Furniture - Emergency Recovery Trolley
Hospital Furniture - Emergency Recovery Trolley


Lockable Gas Spring For Dentist Chairs
Lockable Gas Spring For Dentist Chairs


Lockable Gas Spring for Operation Tables
Lockable Gas Spring for Operation Tables


Lockable Gas Spring For Labour Tables
Lockable Gas Spring For Labour Tables


Hospital Furniture - Labour Tables
Hospital Furniture - Labour Tables


Lockable Gas Spring For Emergency Casualty Trolleys
Lockable Gas Spring For Emergency Casualty Trolleys


Lockable Gas Spring For Passenger Seats
Lockable Gas Spring For Passenger Seats


Lockable Gas Spring For Wheel Chairs
Lockable Gas Spring For Wheel Chairs


Applications In Various Segment

SEGMENTSAPPLICATION
Automobile

Rear Hatch (Dickey), Bonnet
FurnitureOverhead lofts, Cabinets, beds, Ventilators
Auto Bus Body BuildingLuggage Compartment, Engine Flap, Roof top Ventilators, Spl. Mobile Van
Textile MachinesOpening Machine Doors
Generator CanopiesCanopy flap opening
Control Panels
Machine Tool CoversDoors of various control panel
Doors of oil filtration units, EDM wire cut machine flap, Blood analyser, Flaps of various machines
Hospital FurnitureVarious beds, Opration tables, Bed side trolley, Lamps
Garbage Chutes & systems

Garbage chutes & Garbage handling collection of garbage from multi story building.
Counter balancer
Various equipments like tapping machine arms, ENT Microscope, Overhead hospital lamps, CNC machine arms.

Dairy EquipmentsFlaps of Milk Chilling Plants
Metro rail ApplicationControl Panels
Construction EquipmentsLifting Doors of enclosed cabinets
Material handling EquipmentsFor Standing platform, For Handle.
ExportFrance, Australia, Greece

https://en.wikipedia.org/wiki/Gas_spring

Gas spring
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CGI of one type of gas spring

Gas spring with sectional view:
1. Piston rod
2. Head cap
3. Piston rod wiper
4. Piston rod guide bushing
5. Retaining ring
6. O-ring
7. Piston rod seal
8. Cylinder
9. Piston
10. Flow-restriction orifice
11. Piston guide bushing
12. Valve
13. Valve-sealing screw
A gas spring is a type of spring that, unlike a typical mechanical spring that relies on elastic deformation, uses compressed gas contained within an enclosed cylinder sealed by a sliding piston to pneumatically store potential energy and withstand external force applied parallel to the direction of the piston shaft.

Common applications include automobiles (where they are incorporated into the design of struts that support the weight of the hatchback tailgate while they are open) and office chairs. They are also used in furniture, medical and aerospace applications. Much larger gas springs are found in machines that are used in industrial manufacturing (the press tooling industry), where the forces they are required to exert often range from 2500N to 400,000N (forty tonnes).


Contents
1Types
2Forms
3Features
4See also
5References
Types
Gas springs are manufactured in many varieties including:

Standard cylinder
Fixed-height cylinder
Spindle only
Cable cylinder
Stage cylinder
Non-rotating cylinder
Return cylinder (no height adjustment)
Auto-return cylinder with height adjustment
Bouncing cylinder
Dual-mode cylinder
Heavy duty cylinder
Oil damper
Forms
If the internal plunger has a diaphragm which extends to the side of the gas tube, it will cease to move once an applied force is constant and will support a weight, like a normal spring. If a fine hole exists in the plunger, however, it is termed a "slow-dampened spring" and can be used on heavy doors and windows. A gas spring designed for fast operation is termed a "quick gas spring" and is used in the manufacture of air guns and recoil buffers.

Reducing the gas volume and hence increasing its internal pressure by means of a movable end stop, or allowing one tube to slide over another, can allow the characteristics of a gas spring to be adjusted during operation. The rod may be hollow by use of clever seals or may consist of multiple small-diameter rods. A small amount of oil is normally present.

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 of high pressure 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. Passive heave compensators features large gas springs. The stroke lengths can exceed 6 meter.

Features
A variety of features are available from various manufacturers:

Adjustable push-in force via a local knob or remote via a bowden wire.
Single touch release to allow full extension or the ability to lock it out.
Extended stroke through telescoping mechanisms, usually composed of one rod and two cylinders (the smaller of the two cylinders actually acts as a second rod extending in and out of the larger cylinder).
Vari-lift - intended for short production runs and prototypes, 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 reduced in stages, to optimise behaviour. If too much gas is released, a new spring must be installed, and for large quantities, it is better to order a bespoke pressure setting from the maker.
Degressive springs where the spring becomes more, not less, powerful as the main cylinder expands.[1]

Sources and Citations from http://praviauto.com/index.php

Automotive

Tailgate/Dickey, Passenger Bus luggage compartment, Commercial vehicle engine flap:

This is a common application of the gas spring in the automotive sector. The Auto LIFT gas spring adds to the convenience of the user for lifting of the car dickey / compartment door. After an initial manual assistance, the gas spring opens the dickey / door to its designed opening angle.

Engine Hood/Bonnet, Battery/utility compartment, Roof top ventilators:

The above mentioned are common Auto LIFT applications in passenger and commercial vehicles. The gas springs help to keep the respective lids / doors open for as much time as required, and up to the lid's maximum designed opening angle for allowing easy access to the engine bay or the battery compartment.

Passenger Seats, Tilt Steering:

The word luxurious is synonymous with a plush seat in a passenger bus. How much one can recline in a seat is decided by the Auto BLOCK gas spring. Whether one wants to keep the seat backrest upright for reading while travelling or take a nap by reclining it fully, the Auto BLOCK is there for you.

Tilt steering wheels are now a common feature in passenger vehicles. Whether you want to keep the wheel upright for easy ingress and egress or keep it in the bottom position for a more relaxed arm position on the steering wheel, the Auto BLOCK keeps it the way you want it.

Furniture

Filing cabinet lids, Bed & Bed Fittings, Kitchen Overhead cabinets, Study desk-tops:

In places of work, study & homes, the on ground storage space now comes at a premium. The Auto LIFT can be designed to suit your requirements for opening & closing of lids for storage under the beds and over your heads in the filing cabinets & kitchen cabinets.

Swivel Chair height adjustment, Swivel Chair tilt adjustment, Stool:

At your office desk or your study table, you must be able to sit comfortably for your best output. Yet comfort should be assisted by a firm ergonomic (correct height and back-rest angle) sitting position for short as well as long periods of time. The Auto HITE keeps you on the correct height & the Auto BLOCK gives your back, the support it requires. 

Agricultural & Earthmoving Equipment 

Engine hoods, Cabin doors:

On the fields & off the roads, to allow users for easy cabin access, convenient serviceability as well as good ventilation while working, the Auto LIFT does the work here.

Tractor Tilt steering, Joystick:

The Auto BLOCK helps in easing the operation of the joystick and to have a convenient arm position on the steering wheel for the users.

Healthcare Equipment

Dental & Ophthalmic Equipment:

Auto BLOCK & Auto HEIGHT type of gas springs are used in a wide variety of dental and ophthalmic equipments such as the dental chair, in the equipment trolley, the dentist's stool, etc. 

Hospital Beds, Over Bed Food Trolley, Hospital Equipment:

In fowler beds, for easy adjustment of the inclination angle of the patient, Auto BLOCK gas springs are used. In the over bed food trolleys, the Auto BLOCK helps in height adjustment of the table for the patient's comfort during eating.

Industrial applications

Textile Machinery, Packaging M/cs, Sealing M/cs, Printing M/cs:

ll the above applications require lifting of hoods / covers. Here, the duty is done by the Auto LIFT. It increases convenience during the operation of these machines, and aids in maintenance.