The diaphragm or rolling lobe air cylinders are specialty air actuators. Typically, air cylinders have a bit of lag time. That is to say, between the time that the compressed air starts to flow to the cylinder port, and the rod / rod tooling, actually starts to move can be measured. It is not an instant response. It is different for diaphragm or rolling lobe air cylinders.
Diaphragm Rolling Lobe = Almost Instant Response
If you have an application that requires virtually immediate response of your linear actuator, the diaphragm or rolling lobe air cylinder can provide it.
Where there is a need for limited-distance, hesitation free movement the diaphragm rolling lobe cylinders are the perfect solution. They shine in web tensioning applications.
The rolling-lobe type cylinder is ideal for use with electronic regulators. Electronic regulators employ an electrical signal that alters the downstream air pressure to the cylinder. This will vary the cylinder force, allowing the cylinder to respond very quickly in generating greater or lesser rod end force, as the electronic regulator increases or decreases the air pressure to the cylinder ports.
What is a diaphragm or rolling lobe air cylinder then?
Instead of the piston-to-barrel bushings and seals that are found in a traditional linear air cylinder, the piston in the diaphragm or rolling lobe cylinder is attached to a diaphragm which is attached to the end cap. The rolling lobe is depicted in blue in the drawing.
This drawing shows a single acting rolling lobe air cylinder style. These cylinders are also available in spring extend, spring return and also in a double acting formats.
There is No “Sticktion”
Since there is no “sticktion” (Jim Graham’s term for a combination of friction and mechanical impediment to movement) between the cylinder piston and the cylinder barrel, as compressed air enters the cylinder the piston and the rod start to move almost instantly. Movement is free, effortless, almost friction-less.
As the piston travels the length of the cylinder barrel, the diaphragm unrolls (it is a rolling lobe, after all) to allow the piston to travel. Upon the return stroke, the diaphragm re-rolls to its former shape allow smooth rod retraction.
This type of cylinder is reputed to be unmatched in low breakaway force, and repeatability of stroke.
The rolling lobe air cylinder requires no external lubrication source.
The diaphragm, rolling-lobe type cylinder offers a number of mounting styles but the norm is through four threaded mounting holes on each cylinder cap. Clevis brackets or foot mounts are available as well.
Like other types of air actuators, you will need to know the following to help select a diaphragm cylinder for your application:
- What diameter? Force = pressure x area, so the bigger the diameter, the greater force available from a given air pressure
- How much stroke is required for your application
- What size and type of rod thread is required
- Do you need position sensing
- How will the cylinder be mounted
- How will the cylinder rod be connected to the tooling
- Will you need flow controls to control speed