Pneumatic Cylinder Mounting Guide
1. Introduction
In this article, we will deal primarily with the possible mounting options of linear pneumatic cylinders. These include general pneumatic cylinders, tie rod cylinders, round-body cylinders, but excludes rotary cylinders and rod-less cylinders.
In general, the mounting depends on two factors: (i) the required task at hand and the (ii) environmental circumstances. For example, if it is important to actuate in such a way where the displacement travel path (though not the cylinder itself) is non-linear, then a trunnion and/or clevis pin may be needed. Secondly, if one’s circumstances dictate that the cylinder will need to be mounted on the exterior of a machine, then foot mounting may be appropriate.
2. Why is mounting correctly important?
The repercussions of incorrect mounting can be vast. If the mounting is incorrect, then the intended effect is not achieved, failure to maximise lifecycle, or there may be safety risks (in the event of rod buckling). For example, if there is significant side loading, then the piston inside the cylinder body will be subject to non-uniform force, and furthermore, the piston is likely to scrape on one interior side of the cylinder tube. This can lead to premature failure, unnecessary stresses and on the piston and rod connection point. So, it is important to correctly mount a pneumatic cylinder.
2. The Different Mounting Options
Mounting can be split into three broad categories:
- Centreline Mounting
- Offset Mounting
- Fixed Pivot Mount
2.1 Fixed Centreline Mounting
This is an advantageous mounting option if high forces are concerned and the load displacement travel path is linear. This is because there is no side loading (when correctly installed), and all force travels through the centre line. There will be no unnecessary shear forces on the cylinder components.
- Flange Mounting
The most common form of centreline mounting is Flange mounting, either front end (rod end), back end (cap end). These are rectangular or square accessories that attach to the cylinder and then are mounted through threaded screws onto some surface. In some cases, where drilling and tapping is not possible, the flanges are welded onto a surface. Any force proceeds through the centreline during flange mounting and so there is no side loading.
Should I use a Front End Flange, Back End Flange or Both?
This depends on whether the load is being pulled or pushed. If the load is being pushed, it is best to use an End flange, if the load is being pulled, it is best to use a front-end cap. In ideal circumstances, both types of flange (front end and back end) can be used. However, this is seldom necessary in pneumatic applications, where forces are lower than that of hydraulics.
- Centerline Lug
This is no longer a very common mounting style, due to its lack of modularity, and dependence of manufacturer idiosyncrasies. In essence, recentagular tabs are located on the rod end and cap end, but in the centreline of the axial plane. Thus, there is uniform tension force along the cylinder centreline during actuation.
- Tie Rod Mounting
For tie-rod cylinders, there is an accessory that extends the tie rods on either the front side and back side such that they could be mounted. Like centreline lugs, tension force applies along the cylinder centreline. There is thus no shear stress on the mounting bolts. However, tie-rod mounting is not as strong as flange and centreline lug mounting.
2.2 Offset Mounting
In cases where centreline mounting cannot be sought, there are a variety of offset mounting options. In general, since the plane of the mounting surface does not align with the centreline of the cylinder, there will be a bending moment. However, fortunately, the force achieved by pneumatics very seldomly will exceed the yield threshold of the steel or even aluminium of the cylinder body, and, in fact, usually comes no where near it. Offset mounting does not present any practical difficulties for pneumatics for all intents and purposes, unlike in hydraulics.
2.2.1 Foot Mounting
Foot mounting accessories (L brackets or foot lugs) are can be attached to both the rod cap and end cap, and then mounted onto a surface.
- Side Mounting
Side mounting accessories (side lugs) can also be attached to the rod cap and end cap, and then mounted to some surface.
2.3 Pivot Mounts
Pivot mounts are fixed to a surface on one end, but with the help of trunnions and clevises, the cylinder can change alignment in one plane. Forces are also absorbed through the centreline of the cylinder, so there is no side loading. Pivot mounts will require a clevis which is attached to the cap end.
On the other hand, Trunnions can be mounted at the rod end, middle of the cylinder, or cap end, and provides a pivot point for the cylinder. There will be rotation about the trunnion pivot pin. For example, a trunnion bracket can be placed at the end of a roundbody cylinder, with a pin (see figure).
2.3.1 Coupling the Rod to a Mechanical Load
With pivot mounts, it is often also useful to have a rod end accessory that coupe the load with the pneumatic cylinder. For example, Rod-end spherical eyes allows a pivot pin to pass through. Rod end eyes are suitable for linear and non-linear actuation.
Rod End clevis, or rod-end forks, can screw onto a male thread on a piston rod. A Pivot pin can then pass through the clevis.