In all large machines we find a common and very important element, the hydraulic cylinders. These are subjected to great stresses as a result of the severe and extreme conditions in which the equipment is usually used. Therefore, for these machines to work properly, the seals and guides inside the hydraulic cylinders must work correctly.
In the following video we present, by way of illustration, the elements that will be referred to throughout this article. We hope that it will help you understand the important role of the sealing gaskets and guides in the general functioning of the equipment.
Here are some of the most important seals and guides which Epidor Seals and Rubber Technology manufactures and recommends for work in demanding, high-performance areas such as heavy hydraulics.
Index
Seals and sealing guides for large machines
- Piston seals:
They are responsible for the correct sealing between the piston and the cylinder liner, thus ensuring that all the force generated by the oil pressure is transformed into movement. They must be able to maintain a fixed position under load.
It is recommended to fit compact seals, capable of withstanding pressures up to 60MPa (600 bar).
- Piston guides:
As the name suggests, they guide the piston and prevent metal-to-metal contact between the piston and the cylinder liner. They are also responsible for absorbing the lateral forces that may occur due to the demanding work of the hydraulic cylinders. Depending on the load, different materials such as PTFE, phenolic resin (hard fabric) or polyamide are used.
In hydraulic cylinders used in heavy hydraulic applications (pressures between 500 and 700 bar) such as those used in presses, excavators, cranes, etc., a double mounting is usually chosen due to its reliability. What does this mean? That a first stem seal is mounted and immediately after this another stem seal of a different profile than the first one is mounted. 
- Primary stem seal:
The primary rod seal in a high pressure configuration is designed to absorb the total working pressure of the hydraulic system. In addition to withstanding this pressure, it is also responsible for absorbing possible pressure peaks due to the demanding work of the cylinders and machines on which it is mounted. The primary seal leaves a small film of lubricant on the piston rod so that the elements after this seal do not work dry and, therefore, do not wear out prematurely. These elements would be the secondary seal and the wiper.
- Secondary stem seal:
The secondary seal, so called because it is in the second position in relation to the cylinder working chamber, has the main purpose of minimising the oil film remaining on the piston rod from the primary seal. In case of failure of the primary seal, the secondary seal would take over the role of the primary seal.
- Scraper:
The function of the scrapers is to protect the inside of the cylinders from the entry of contaminants from the outside. Both the seals and the guides working inside the cylinders need to work under optimal conditions: no dust, moisture or any environmental influence. When working under these conditions, their useful life is excessively reduced, the operating fluid is contaminated, and the cylinder will most probably stop working properly, and the machinery will have to be stopped for repair.
- Stem guides:
They are responsible for guiding the piston rod and preventing metal-to-metal contact between the piston rod and the hydraulic cylinder head. In addition, they are responsible for absorbing the lateral forces that may occur due to the demanding work of the hydraulic cylinders. Depending on the load, different materials such as PTFE, phenolic resin (hard fabric) or polyamide are used.
At Epidor Seals and Rubber Technology we can advise you on what sealing solutions can help keep your large machines running smoothly. You can contact us at following form.