Cable Cylinders;
Concept & Applications

Cable Cylinders

Cable cylinders are pneumatic air actuators (cylinders). They are "rodless" air cylinders, but don't use a band type sealing method as band cylinders do.

Rather than having a piston rod sticking out one end of the air cylinder or the other like stanard “rodded” air cylinders, cable cylinders use a cable which enters either end of the cylinder barrel, and is attached to either side of the internal piston.

The cable exits the cylinder barrel through the cylinder end caps, winds around a shiv or pulley on either end of the cylinder barrel, and joins outside the cylinder barrel in a non-supported carriage.

Then, as the piston inside the cable air cylinder moves from end-to-end, the cables extending out the ends of the cylinder move as well, and depending on the direction of the piston, the carriage and the on-carriage tooling moves towards one end of the air cylinder or the other.

As with rodless cylinders in general, the carriage moves within the length of the cylinder barrel. The benefit of this is space saving. A typical NFPA type cylinder has a cylinder rod that protrudes from on or either end of the cylinder. Depending on the length of the rod, the overall length of the cylinder will more than double the length of that rod.

The cable cylinder also allows the carriage to be located some distance from the actual barrel and piston unlike almost any other kind of air cylinder.

Another significant benefit of a cable-type air cylinder is it’s relatively low cost per inch of stroke.

Let’s take a look at some of the items that make up a basic cable cylinder. Of course, each manufacturer will have their own styles and design differences. The drawing just below will give you a good idea of the concept.







Item 1

The barrel of the cable cylinder is usually round, though, as long as the piston would move easily, there’s no reason why it couldn’t be elliptical or octagonal.

Barrels can be made of steel, aluminum or composite materials and can be many feet in length. As the length of the barrel increases, so too does the need to provide barrel supports to ensure that the cylinder barrel stays straight.

The cable cylinder manufacturer will provide load characteristics for their cylinder.

A drawback of the typical cable cylinder barrel is that it does not lend itself to attaching proximity switches easily. Some manufacturers have overcome this by design. If there is a need to determine the position of the load from the position of the magnet on the piston, then thought must be given as to how to install magnetic sensors on or near the cable cylinder barrel.

Item 2

This is an end cap in the center of which is a hole through which the cable passes from the end of the cylinder.

The cable will pass through the hole, and seals in the end around the cable will help ensure that compressed air doesn’t escape. Cable cylinders are notorious for leaking through these seals, as if there’s ever any sideloading of the cable it would tend to wear these end cap seals quickly.

The end caps can be cushioned to decelerate the piston, though it’s almost always far better to stop the piston travel by having the carriage stopped externally.







Item 3

This is the sheave or pulley which is attached to the end cap on both ends of the cable cylinder. The cable, attached to the piston inside the cylinder, travels through the end cap, around the sheave, and is ultimately attached to the carriage.

Item 4

This depicts the cable. One of the significant benefits of the cable cylinder is that the cable can be relocated elsewhere via a series of sheaves, and, when the piston inside the cable cylinder barrel moves with incoming compressed air, the carriage will move regardless of how far away from the cylinder it travels. The carriage travel could even be tangential to the orientation of the cylinder itself.

Please see the picture below to better understand the concept.







Depending on where extra pulleys are placed, and when wiring the cable in a “block and tackle” type configuration, the weight moving capacity of the cable cylinder and the carriage travel distance can be lengthened or reduced.

Item 5

The carriage on a typical cable cylinder is fairly light duty, meant only to attach the carriage to a load with a couple of bolts.

By the design of the cable cylinder, the carriage typically is unsupported. Therefore, the use of rails and bearings to carry the load, and the use of the cable cylinder carriage only to provide linear motion to the load, is the norm.

If the cost of providing a carriage support is high, perhaps using a typical band cylinder with integral support might be best.

The cable cylinder manufacturer will provide load characteristics for their cylinder.

Item 6

This depicts the piston. Different manufacturers offer different piston designs, yet all will have piston seals, an ‘O’ ring or ‘D” ring, or multiple rings around the circumference of the piston.

There may also be a magnet to allow piston position sensing.

What do you need to know to select the appropriate cable cylinder? Here is a check list: