Actuator Technology Center

What do you need to know to select the right air cylinder from the huge variety available in the industrial marketplace? Here is the answer.

How much force do you need to move the object you wish to move?

You’ll need to know the weight of the object. Consider what the object being moved is sliding and know that this friction is adding to the load.

Oversize the required force of the cylinder by 25% to take into account friction of the rod and piston seals within the air cylinder itself, and also allowing a safety margin as it relates to the expected load the cylinder will see.

Know your available air pressure (example: 90 PSI) and multiply that times the surface area of the piston inside the cylinder to get the theoretical output force of the cylinder.

If you multiply 3.14 x the radius - in inches -squared this equals the surface area of the piston in square inches.

Since cylinders only come in certain bore sizes, default to the standard cylinder bore that’s the next size up if none are exactly the bore diameter calculated. Note that the size of the outside of the cylinder on some types has no real bearing on what the piston diameter inside the cylinder is.

How far do you wish to move the object?

If you wish to move the object five inches, it’s logical to think that the cylinder piston / rod travel needs to be five inches. It could be that simple. It might not be. Take into account the size of the object that’s to be moved to be sure that the object itself doesn’t impact on the cylinder rod cap on retract.

You may wish to consider a cylinder with a longer stroke than required so that the piston of the cylinder can be stopped inside the barrel by having the object itself stop the movement. This stops the piston from “bottoming out” on either cap of the cylinder itself. Depending on the cycle speed, this may increase cylinder life.

Take into account how you are connecting your load to the cylinder rod. If using a clevis of some sort, take that dimension into account.
Regardless of what is attached to the end of the rod, the rod itself can only move the distance that the piston inside the cylinder can move. That’s all the stroke distance you have to work with.

How will you attach your object to the cylinder rod?

Careful, if you screw the object onto the rod thread directly. Make sure that the “load” and the rod are aligned.

A rod clevis is a “sloppy” connector that screws onto the end of the rod thread. Bolt the other half to your object, and the two halves are connected in the center via a cotter pin of sorts.

This “sloppy” type of connector forgives some misalignment between the rod travel and the object movement for if the object is too far off the axis of the rod, you will very quickly encounter problems with the air cylinder.

There are alignment couplers commercially available that will further absorb misalignment between load and rod. For extreme misalignment cases, the load can be installed on rods external to the cylinder, removing almost all side-load from the rod itself.

Note that there are standards in rod thread size which change depending on the bore size of the cylinder.

Further, the rods themselves can be modified to reduce the size of the thread, to change the type of thread, to make the rod end a female thread, or to replace the standard rod thread with a stud that can, if the stud breaks, be removed and replaced at minimal cost to parts and downtime.

How will you attach the cylinder to your machine?

Depending on the type and size of cylinder there are many options of unique and standard mounts.

Most cylinders come with integral mounting of some sort, whether it’s a rod-cap thread, a rear-cap thread, a rear tang for a clevis mount, threaded holes into which bolts can be turned, front or rear flanges, trunnion mounts…and so on. It depends on the type of cylinder.

Remember, if the load that’s being moved is not aligned with the rod travel, you will have problems. Therefore, the type and location of load will help determine the type of cylinder mount too.

What type of cylinder?

Some choices are:

FRL is an acronym for Filter, Regulator and Lubricator, devices used to “condition” the compressed air from a compressor before it gets to your application be that through an air valve to air cylinders, powering air tools and so on.

When called in to troubleshoot a complaint from a client that their compressed air filter, regulator or lubricator wasn’t working, the first response is to ask the symptoms. Common complaints are, “the regulator is not working, and it’s leaking oil“, or “my air filter fills up too quickly”. Have you ever had these problems?

The acronym FRL is placed in this order deliberately.

These air treatment units, whether they are an assembly (combination FR + L) or a number of single components - Filter + Regulator + Lubricator - installed in a row, must always be installed with the Filter first, the Regulator next, and the lubricator last.

The filter must ’see’ the air coming from the compressed air supply line first, as it’s the defense against compressed air-borne water and particulates. If you think about it, you would want the filter to remove contaminants and free water from the compressed air before that air gets to more sensitive down-stream components, including the regulator and the lubricator.

The regulator is installed after the filter to ensure that the air getting to the regulator is as clean as that type of compressed air filter will allow, thus increasing the life span and mean-time-between-failures for the regulator.

The regulator’s purpose is to regulate a lower pressure to the downstream application. Some folks are of the opinion that the regulator can be used to “dial-up” the pressure. This is true, as long as it’s understood that the pressure that’s being selected is at a level below the upstream supply pressure. You cannot use a regulator to increase the pressure downstream higher than the supply pressure upstream of that regulator.

Compressors are usually cyclic, meaning that the air pressure in the lines from them varies according to where the pressure is in the compressor receiver. When the air pressure in the compressor receiver falls to the low level set point, the compressor will kick in, and bring the pressure in the receiver up to the high level set point, at which point the compressor will stop. This cycle repeats, sometimes quite quickly, depending on the compressed air demand in the shop. A regulator will dampen the pressure swings from the system as the compressor kicks on and off, ensuring that your application, if the regulator pressure is set at the correct level, will see a constant, steady pressure.

If the regulator is incorrectly installed, upstream from the filter instead of after it, not only is the regulator not protected from air-borne water and particulates, it will negatively affect the flow of air to the filter, decreasing its effectiveness.

The lubricator’s purpose is to provide a steady, metered stream of the appropriate lubricant to the downstream application, be that an air tool, or an air valve / cylinder combination.

The lubricator is installed last in the FRL series to ensure that the lubricant has ready access to the components desired to be lubricated though many modern pneumatic circuits may not need a lubricator at all, what with the high cycle type lubricants that are commonly used by air actuator manufacturer’s.

If the lubricator is incorrectly installed after the filter and before the regulator, the lubricant flow will negatively affect the operation of the regulator. The regulator may be over lubricated to the point where it doesn’t work properly. This may be the cause of the “lubricator’s all gummed up and not working properly” complaint. Most compressed air regulators are relieving type, and if the lubricator is “feeding” lubricant to the regulator, lubricant will wick from the relieving port, hence the “regulator’s leaking oil” complaint.

If the lubricator is installed upstream from the filter and the regulator, the lubricant stream from the lubricator will simply be intercepted by the filter, and not get downstream to the application at all. Thus the filter is “filling up too quickly” complaint.

In the absence of the lubricator, the correct installation if filter first, then regulator.

If the unit you have is a combined filter regulator, it’s internally plumbed to have the air filtered through the filter ‘half’ before the compressed air gets to the regulator.

Remember, it’s FRL on purpose!

Bill Wade is a former sales representative, sales manager, marketing manager and president of companies that use and sell compressed air, along with other equipment and supplies. His sales agency currently represents a select group of companies. Mr. Wade writes about understanding compressed air, how it’s compressed, how it’s treated, and how it’s used at http://www.about-air-compressors.com.

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There are two main types of electric motors. There are direct current or DC and alternating current or AC motors. The reference of DC or AC refers to how the electrical current is transferred through and from the motor. Both types of motors have different functions and uses. Dc motors come in two general types. They can have brushes or be brushless. AC motors, as well, come in two different types. They can be two phase or three phase. The differences in DC and AC motors are sometimes subtle, but these differences are what make one types better for a certain use.

Direct current or DC electric motors work for situations where speed needs to be controlled. DC motors have a stable and continuous current. DC motors were the first and earliest motors used. They were found, however, to not be as good at producing power over long lengths. Electric companies found using DC motors to generate electric did not work because the power was lost as the electric was transmitted. Brush DC motors use rings that conduct the current and form the magnetic drive that powers the rotor. Brushless DC motors use a switch to produce the magnetic drive that powers the rotor. Direct current motors are often found in appliances around the home.

Alternating current or AC electric motors are used differently based on what type of AC motor it is. Single phase AC motors are known as general purpose motors. They work well in many different situations. These AC motors work great for systems that are hard to start because they need a lot of power up front. Three phase, also called polyphase, AC motors are usually found in industrial settings. These motors also have high starting power built transmit lower levels of overall power. AC power gets its name from the fact that it alternates in power. The amount of power given off by an AC motor is determined by the amount of power needed to operate the system.

DC and AC electric motors are found everywhere from the home to the car to industrial plants. Motors are important to everyday life. Dc motors were introduced and caused a great revolution in the way many things are done. When AC motors came on the market the way motors were looked at changed because of their amazing starting power potential. DC motors and AC motors are different in many ways, but they still both are usede to power the world.

http://electricmotors-hq.com Everything you need to know about electric motors from their history to buying new and used.

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