What is a Rod Seals
Rod seals are a common type of sealing device used in a wide range of industries and applications. While there are many aspects of rod seals that may not be known to everyone, they are a valuable sealing device that can be used to prevent the passage of fluid or gas.
Basic Principles For Rod Seals Selection
The allowable values of speed, temperature, working medium and oil content of the piston rod determine the rod seal form and seal material. Each key influencing factor is discussed below.
Operating Temperature
The temperature of the seal, especially the actual temperature of the working lip, directly determines the life of the sealing system. In addition to the temperature of the working environment and working medium (usually hydraulic oil), the factors that also affect the seal include working pressure and working speed.
Our experience is that under the influence of certain working pressure and working speed, the temperature of the working lip of the rod seals may be 10~80°C higher than the temperature of the working medium (when the piston rod movement speed is 0.5m/s and the pressure is 35MPa , the working lip temperature is about 80°C higher than the hydraulic oil temperature), so when selecting seal materials, please carefully consider the effects of pressure and speed on temperature.
The working temperatures of commonly used sealing materials are as follows:
| Material | Operating Temperature/℃ | Material | Operating Temperature/℃ |
| Nitrile rubber | -30～100 | Fluorine rubber | -10～150 |
| Polyurethane | -30～110 | Polytetrafluoroethylene | -200～260 |
| Nylon | -50～120 | Phenolic resin | -55～120 |
| Polyacetal | -40～140 |
Working Speed
The friction power is proportional to the movement speed of the piston rod. For high-speed moving seals, appropriate sealing forms and materials must be considered.
| Working speed m/s | Recommended sealing material | Recommended sealing form |
| <0.2 | Rubber, PTFE | U-shaped ring, RSJ type combined seal, universal plug seal (O-type spring) |
| 0.2～0.5 | Polyurethane ,PTFE | U-shaped ring, RSJ type combined seal, universal plug seal (V-shaped/slash spring) |
| 0.5～15 | PTFE | RSJ type combined seal, universal plug seal (V-shaped/slash spring) |
Work Pressure
The direct side effect of excessive working pressure on the rod seals are extrusion of the seal, and seal strain due to high friction. Commonly used methods to deal with high-pressure work pressure:
1. Choose seals with larger working cross-sections.
2. Add a retaining ring.
3. Use multi-channel sealing (pay attention to the sealing structure, some seals cannot be used in series).
4. Choose sealing materials with small friction coefficients.
| Working pressure/MPa | It is recommended to use sealed form |
| <2 | U-shaped seal (smaller cross-section); Universal plug seal (O-type spring, slash spring); Dashi Feng DS R |
| 2～7 | U-shaped seal (standard cross-section); Universal plug seal (O-type spring, slash spring); Dashi Feng DS R |
| 7～15 | U-shaped seal (larger cross-section) + retaining ring; Universal seal (V-shaped spring, slash spring) + retaining ring; Dashi Feng DS R |
| 15～30 | U-shaped seal + back-up ring (larger cross-section) + RSJ-type buffer seal; Universal plug seal (V-shaped spring, slash spring) + retaining ring; |
Working Medium
The influence of the working medium on the rod seals mainly lies in two aspects: the swelling of the sealing material in the working medium and the lubrication and protection ability of the medium on the seal. Commonly used sealing materials work well in ordinary hydraulic oil, while ordinary polyurethane and nylon are not resistant to hydrolysis.
Work Itinerary
The size of the working stroke directly affects the lubrication of the rod seals and other seals. If the stroke is too large or too small, it will cause poor seal lubrication. An effective solution is:
1. Use polytetrafluoroethylene, a sealing material with extremely small friction coefficient and self-lubricating, and the specific selection is such as pan plug seal;
2. Design an additional lubrication mechanism to lubricate the seals;
3. Choose a sealing structure that has better lubrication for the seal itself, such as a pan-plug seal, DSR seal, etc.
