Innovative motion control solutions since 1947

Category: Pneumatic Cylinder

Different Types of the Pneumatic Cylinder

A pneumatic cylinder is a type of appliance that makes the use of power that is generated from compacted gas in order to form a force in interchanging linear motion. A pneumatic cylinder may also be referred to as an air cylinder, as the term pneuma, means air. Very similar to hydraulic cylinders, a force is applied into the piston, which pushes it to the desired direction. The piston that is part of a pneumatic cylinder is a disc or a cylinder. The force that is created is transported by the piston rod to the object that requires moving. A minority of engineers prefer this device due to its cleanness, quietness, and minimum space for storing fluids.

Purpose and Type

The shape, material, and size of the cylinders depend on the purpose one is using them. The different materials that are used for pneumatic cylinders include stainless steel, steel, nickel-plated brass, and aluminum. The way the materials are chose for the devices involve considering several factors such as amount of loads, specific stroke length, temperature, and humidity. The devices also come in a wide range of body constructions, which include:

  • Flanged- type cylinders – the ends of these cylinders feature fixed flanges.
  • Tie rod cylinders – these are the most common type of cylinder structure and find their use in a huge variety of loads. These are also proven the safest form to work with.
  • Threaded end cylinders – in these, the ends tend to attached to the tube body.
  • One-piece welded cylinders – the ends of these cylinders are welded or crimped to the tube.

A Further Look into the Types

The three pneumatic cylinders we discuss below are:

  • Single-acting cylinders
  • Double-acting cylinders
  • Telescoping cylinders

Single-acting cylinders (SAC) use pressure that forms from compacted air. In majority of cases, the extension SAC cylinders have is very limited due to the amount of space the compacted spring takes.

Double-acting cylinders (DAC) use air pressure in order to retract strokes and move in range. Two parts make up this cylinder, both of which let the air in. One is for outstroke and the other, in-stroke.

Telescoping cylinders, also known as telescopic cylinders come in single-acting and double-acting modes. Their designs allow for much longer strokes and tend to be reserved for uses where the piston has to face minimal side loading.



The Safe Application of 3-Position Pneumatic Valves

Many pneumatic valves are fairly straightforward things — they’re open, or they’re shut, and it’s pretty clear when they should be in each position. But 3-position pneumatic valves with double-acting cylinders can be confusing.

3-position pneumatic valves are able to stop an attached pneumatic cylinder in mid-stroke, either ceasing motion or — their intended purpose — ‘jogging’ the cylinder for a heartbeat in mid stroke before continuing to extend or retract normally.

Often, such complexities are requested when they’re not needed, because the engineer designing the system believes that such a three-position valve is needed as an emergency response: if, for example, power cuts out in mid-job, they believe the third position is a useful way to prevent damage to the system.

In fact, that’s not the case; instead, two-position, detended pneumatic valves should be used on clamps and other devices to maintain cylinder position if power is unexpectedly removed. A spring-return, two-position valve will also work if no pinch point exists or the cylinder is moving in a guarded action and can return to its normal position safely.

The problem with using 3-position pneumatic valves as ’emergency response’ is that there is no position in which such a valve is actually safe during an extended power cut.

  • If the valve is in the all-closed position, the cylinder will be pressurized on both sides, which can lead to drift if the cylinder isn’t perfectly sealed.
  • If the valve is in the ‘let air in’ position, the cylinder will immediately move toward the extended position because of the higher surface area on the can end of the piston than the rod end.
  • If the valve is set to ‘let air out’ position, the cylinder will immediately move toward the retracted position because there will simply be no pressure present to maintain the extension.

There is a fourth scenario — if the 3-position valve is set to ‘let air out’ position and the circuit has a dual pressure system designed to provide ‘make-up’ pressure to overcome any leakage (which almost always comes with check valves in place to keep the cylinder pressurized against unexpected loads), the 3-position pneumatic circuit doesn’t suffer terribly in an emergency outage. However, this is an incidental byproduct of a system created for other purposes, and using a system like this as an emergency measure is expensive and less reliable than the aforementioned system of detended two-position valves and spring-return valves.

How to Improve the Life Expectancy of Your Gas Springs, Pt. II

In the first part of this extended article, we talked about how to extend the life expectancy of your gas springs — and here, we continue that conversation. Let’s get right back into it.

Things to Avoid
To keep your gas springs working better, longer, never use the bottom of the spring as the strike surface — the top of the piston rod is the correct option. Rather than using improper or inadequate guidance, which can lead to side loading due to axial misalignment, us guide retainer sets, roller bearings, wear plates, and a hardened strike surface. That will extend spring life as well. Anything more than a single degree of side load on the piston rod is asking for a gas spring that fails years earlier than it could.

Along that same vein, avoid contaminants. Even minor contamination within a die can cause premature failure. Die designers ought to specify drainage holes in the spring pockets so that fluid doesn’t pool around the springs. Gas springs shouldn’t be exposed to caustic draw-die compounds or other contaminants; if your production line makes this a necessity, contact the gas spring’s manufacturer to talk about what protective measures you can take.

Preventative Maintenance
Of course, any discussion of extending the functional lifespan of any piece of equipment, from gas springs to pneumatic cylinders, needs to touch on the cornerstone of equipment care: preventative maintenance. Sound preventative maintenance procedures require users to check the pressure, temperature, and physical condition of the springs for signs of wear.

If a random sample of springs in a die exhibit signs of being overworked, overpressured, or overheated, every other spring should be examined as well. A significant variation in spring pressure or condition could indicate a flaw in the die’s design, build, or operation. If a specific spring’s pressure is low, check for leaks, then recharge and check for leaks again.

The physical condition of a spring should be determined with a visual examination; there should be no need to dismantle the spring. Worn springs that are still viable should be rebuilt. If the rod is damaged, it obviously will need to be replaced as well.

Following these four major areas of care should help any project keep its gas springs lasting as long as their construction allows — good luck!

Why Do I Need an Air Regulator?

Air regulators are pneumatic devices that receive air at any pressure within its tolerance, and then dispense air of a pressure no greater than their intended output. In other words, air comes in at a higher pressure, and departs at a lower pressure in most circumstances. For the purposes of this article, everything that comes before the air regular is ‘upstream’, and everything after it is ‘downstream.’

Air flows from an air compressor somewhere upstream, and it may or may not interact with other upstream elements. When it reaches the air regulator, a system of springs and an internal diaphragm ‘pushes back’ against the incoming air, offering enough resistance that only a set volume of air (and thus, a set air pressure, since air pressure is calculated by volume within a given area) moves downstream. So long as the upstream pressure is enough to open the diaphragm, and not enough to tear the air regulator off of the device altogether, the downstream pressure will be constant regardless of how the upstream pressure changes.

This is a hugely vital function, because many pneumatic cylinders would be harmed by overly powerful air, or at the very minimum the jobs the cylinders are doing would be done poorly if they were done too quickly. For example, without an air regulator, a pneumatic cylinder attached to a carefully-balanced load might jolt upward too quickly and disturb the load it was lifting.

The air compressors have a ‘cutoff point’ at which they stop compressing air, instead allowing the air already compressed into their reservoir to do the work. Air regulators will cause the upstream system to back up such that the upstream pressure will eventually build up and cause the compressor’s cutoff point to trigger, stopping the compression until that high-pressure air has had a chance to work its way through the regulator enough that the air compressor restarts — but the downstream pressure from the regulator never changes until the entire system is shut down and the diaphragm finally closes.

The answer to the title question, then, is simple: you need an air compressor not only to protect delicate devices or delicate work from variations in the upstream air pressure, but to reduce the amount of air that your compressor has to process.

An AirStroke Actuator May Be Better Than Springs or Hydraulics For Your Needs

AirStroke actuators made by Firestone perform the same kinds of actuation tasks as the more commonly seen hydraulic and pneumatic cylinders, but for short-stroke, high-force tasks, have several advantages over their peers. AirStroke actuators are friction-free, leak-free, single-acting pneumatic actuators that have been used in a huge variety of industrial environments in the place of hydraulic or pneumatic cylinders.

You’re probably familiar with the traditional design of one of those cylinders: a tube of steel with a piston of steel inside, filled with either gas or hydraulic fluid. As more gas or fluid is added, the piston is pushed outward by the increase in pressure. Because the piston must be sealed tightly enough that the gas or fluid cannot escape, they require both constant lubrication and an environment free of particulate that might degrade the seal.

Firestone’s AirStroke actuators don’t have moving parts or seals, so they neatly sidestep both of those problems. They need no maintenance or upkeep, because they consist of naught but a strong, flexible outer wall that forms a tube capped on both ends by metal. When it’s empty, the outer wall collapses perfectly downward so that the metal caps are almost resting on top of one another. The metal endcaps have ports that allow air or fluid in and out; as the medium of choice rushes in, the endcaps are forced apart and the walls expand upwards, doing the job of a pneumatic actuator but with dramatically increased flexibility — they can operate with the top cap up 30 degrees off of vertical without a noticeable loss of power or efficiency.

With diameters between 2.2 inches and 37 inches, stroke lengths of up to 14 inches, and workloads of up to one hundred thousand pounds, AirStroke actuators can do almost any short-stroke, single-action job you’ve got. At less than 60% of the up-front cost of a similarly-purposed pneumatic or hydraulic cylinder and zero maintenance and upkeep, from an economic standpoint, the AirStroke is practically a no-brainer.

If you’re not certain whether or not an AirStroke actuator is the right tool for your job, contact Peerless Engineering today. We’ll be happy to offer you a free consultation on the powers and properties of these amazing industrial implements.