# Analysis of Different Guide Elements' Designs in Hydraulic Cylinders
## 1 Introduction  
Hydraulic and/or pneumatic components are important for various machines where high loads, redundancy, and rigidity are required in the system, especially in agriculture, forestry, automotives, aviation, construction, etc. Various types of oils or water-based fluids--water, ionic fluids, etc.--are commonly used for power transmission in hydraulics [1; 2; 3; 4; 5; 6], while air is used in pneumatics [7]. Hydraulics are widely used in many industries because they have many advantages, such as simple operation, mobility, high power density, fast automation, good overload protection, and fast change of motion [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. Their disadvantages are their relatively low efficiency compared to mechanical drives, their possible internal losses, the compressibility of the fluid, the high associated working and manufacturing costs, their relatively expensive maintenance, etc. [7; 19; 20; 21]. The energy stored in a pressurised fluid is converted into a linear or rotary mechanical movement. Almost all types of hydraulic cylinders (HCs), regardless of the guide elements, use elastomer seals that prevent leakage between the chambers or the environment [22; 23; 24; 25; 26; 27]. Seals and wipers are used to prevent contaminants such as solid particles and water from entering the hydraulic cylinder. The seals cause friction and wear on the contacting components, and if the damage is large enough, leakage will occur. Leaks can lead to a reduction in volumetric efficiency and damage, as well as pollution [14; 28; 29; 30; 31; 32; 33; 34; 35; 36]. The frictional forcebetween seals and mating surfaces in relative sliding motions has a significant influence on the performance, reliability, sliding behaviour, and wear of seals/mating surfaces [37; 38]. The system pressure can significantly influence the frictional behaviour of different guide elements, impacting overall performance and wear. The choice of guide element has a great influence on the pressure distribution. Figure 1 shows the efficiency and pressure distribution for different types of guide elements [39]. An incorrect choice of seal material or seal geometry, insufficient surface roughness, and lubrication can lead to inadequate seal performance or other tribological factors resulting in high friction, poor seal performance, and low system efficiency, as well as higher operating costs [37; 40; 41; 42; 43]. Conversely, reducing frictional forces improves the performance and efficiency of hydraulic cylinders (or other components), extends their service life, and expands their application range in a variety of industrial environments [37; 42].  
[PERSON] et al. [37] described the design of a new test rig for measuring frictional forces in pneumatic components and seals. [PERSON] et al. [40] proposed an experimental study on the influence of different seal geometries in pneumatic cylinders and operating conditions on friction behaviour. The experimental tests were carried out on industrial, commercially available pneumatic cylinders, whereby pistons and rod seals were tested separately in order to investigate the frictional behaviour of the individual seals. [PERSON] et al. [41] presented an analytical model, with its experimental validation of a pneumatic differential cylinder and a double-acting hydraulic cylinder with a double piston rod. [PERSON] et al. [42] proposed a redesign of the interface between the front head and the guide bearing of a linear pneumatic cylinder. The design changes were made using finite element analysis. In [14; 37; 40; 41; 42], the authors dealt with the frictional force of the seals of pneumatic cylinders. The objective of this paper is to evaluate the frictional force of a hydraulic cylinder with different designs of the guide elements (guide ring, labyrinth seal, and hydrostatic bearing) used in industry at different pressures and radial loads and to consider them as a whole.