What do they do? What problems do they solve?  

Whatever the material, wear rings, also known as guide rings, aptly named for their guiding functionality, can be a key component of a hydraulic system. In general, wear rings can extend the life of a hydraulic system, as they are faster and less expensive to replace than an entire cylinder. They also increase equipment availability and up-time, which is critically important in the fluid power industry.

How do they work?

In hydraulic cylinders, wear rings typically provide support to the piston or rod to help guide movement and optimize seal performance. Designed to accommodate radial loads, they prevent contact between the piston and bore or rod and cylinder head, and act as a wear component in the assembly. 

How do you know if you need a Wear Ring?

Nearly every sealing configuration in a hydraulic cylinder requires a wear ring. Choosing the best material for an application is a matter of evaluating the type of application, the size of the load within the system, the installation space, and the mating surface. 

What are the advantages and disadvantages of each wear ring type?  

Wear rings are available in metallic and nonmetallic options. While metal wear rings are appropriate in some applications, nonmetallic wear rings offer numerous benefits for hydraulic cylinders in fluid power applications such as off-highway, material handling, industrial machines, mobile hydraulics and agricultural equipment. Nonmetallic wear ring materials include PTFE-based compounds, as well as thermoset plastics and thermoset options. Each has its own specific characteristics.

PTFE-based wear rings provide extremely low friction within hydraulic systems and are particularly well-suited to dry-running applications, mated with steel, aluminum or cast iron. Their smoothness generates so little abrasion that, in some cases, they allow for the use of less expensive hardware in a system. The low friction characteristics of PTFE-based wear rings also help reduce the incidence of stick-slip when starting up the system. As a result, PTFE-based wear rings commonly feature in equipment operating at high temperatures and pressures.

Thermoset wear rings have outstanding wear resistance properties and offset heavy loads at low speeds, addressing application demands for strong, light, durable wear rings. Although thermoset wear rings are dense, they are elastic in comparison to metal rings.

Thermoplastic wear rings are the workhorses of hydraulic systems commonly featuring in internal valves and compressor components. In many systems, they are temperature-resistant and can provide a high level of performance at a more affordable price than PTFE-based or thermoset wear rings. Most thermoplastic wear rings can mate with steel, hard chrome-plated surfaces, and cast iron.  
 
Advantages of nonmetallic wear rings 

• Favorable friction behavior 
• High load-bearing capacity 
• Easy installation 
• Damping of mechanical vibrations 
• Good wiping effect 
• Protection of seal against "dieseling", the hydraulic fluid flowing too quickly across the cylinder 
• Elimination of local stress concentrations 
• Less downtime because of damage to rods or pistons, and longer product life 
• Reduced maintenance requirements due to elimination of the need for lubricating grease  

What are the important application-specific criteria for choosing the right wear ring type, size, material, etc.?

Tolerance is the most critical criteria. Machined high-volume commercial wear rings can have wide tolerances, typically up to 0.005 inches of the total wall. Precision machining produces wear rings with tighter specifications and lower tolerance stacks. Though higher in cost, they offer a lower total cost of ownership because they fit better between parts and reduce the risk of premature seal and system failure. This pays dividends within systems marketed as high performance and judged on their longevity. 

It is also important to consider system operating conditions, such as temperature, expected radial load, operating speeds, and chemical compatibility with operating fluids.

How do you choose the right wear ring to achieve the best design? 
It is important to partner with an experienced wear ring supplier that understands the needs of an application to help choose the best system solution. High speed and low load cylinders need a material that can tolerate high pressure-velocity and dissipate heat, as well as one that handles pressure and that is not prone to stick slip, a phenomenon which causes vibration and noise.