How to Choose the Right Material for Your Custom Seals

Regular maintenance is the key to prolonging the life of industrial and manufacturing machinery. Like all other pieces of machinery, maintaining the hydraulic systems prolongs their service life and ensures optimal performance of these systems. Of all the parts in a hydraulic system, hydraulic seals are the most frequently inspected and oft-changed. These ring-shaped seals fit into machined grooves in a piston or the wall of the bored space where the rod passes through as it transfers linear energy. In this article we’ll be going over the importance of seals, the forces they are exposed to, and some of the most common seal materials to help you make the right choices for your next custom seal.

The Importance of Seals

The piston seal helps maintain pressure in a hydraulic cylinder by not allowing hydraulic fluid to escape between the piston and the bore. In the case of a rod seal, as the rod transfers the linear force from the piston, the seal in its casing prevents pressure loss and, at the same time, evenly spreads a minute amount of hydraulic fluid as a lubricant.

The other function of a piston seal in a hydraulic system is to work in unison with spacer rings to prevent metal-to-metal contact between the piston and the bore, or in the case of a rod seal, the connecting rod and the housing. Metal-to-metal contact creates friction, and its chief byproduct is heat. Heat is the biggest enemy of a hydraulic system and will ruin seals. The damage then quickly moves on to pistons, rods, and bore surfaces. 

You can appreciate the role of a seal in a hydraulic system.

Primary Seals & Backup Seals

In many piston seal applications, there are primary seals and backup seals, also known as secondary seals. The primary seal receives most of the forces exerted in the hydraulic cylinder and is made from the most durable materials. Backup seals are meant to back up the primary seal and are often made from a less expensive material.

The Forces Exerted on a Custom Seal

When evaluating what type of custom seal material you need for an application, there are three areas to consider. 

Chemical resistance

The seal comes into contact with hydraulic fluid. Synthetic-based hydraulic fluids are the most common, followed by water-based and biodegradable ones. Manufacturers blend some hydraulic fluids for higher viscosity, others to withstand higher temperatures, while other blends resist oxidation or shear stability, and others are blended for a combination of these traits. It is essential to ensure the seal material you choose for your custom seal is compatible with the type of hydraulic fluid used in that application. For more information on fluid compatibility, refer to this chart from Hallite.

Temperature

Any mechanical process involving moving parts causes friction. The chief byproduct of friction is heat. If the heat generated by a process is more than the seal material can withstand, the seal will fail, and more expensive components will be damaged.  

There are also considerations when working in cold environments. Lower temperatures make seal materials brittle and less pliant. It is important to match your seal material to your working environment. Using a bulldozer in California presents few seal problems, but that same bulldozer in North Dakota or Alaska faces different issues in the extreme cold.

Pressure

The hydraulic process uses pressure to push a piston and achieve linear movement. Hydraulic fluid under pressure, like any fluid, will seek the path of least resistance. One of these paths is the minute space between the piston and the wall of the bore or cylinder. The seal material needs to be able to withstand this pressure. If the material is too soft for the pressure in that particular hydraulic process, the seal will deform and allow fluid to escape. Another form of failure is when compression forces the seal material to deform into the space between the piston and the bore, a condition known as extrusion.

Types of Seal Materials

Seals receive the greatest pressure in a hydraulic system, so they wear out quickly. From an engineering standpoint, that’s acceptable because seals are less expensive than the other components. Even so, engineers prefer to get as much life out of a seal as possible. A well-functioning seal maintains the integrity of the hydraulic system for an extended period of operation and minimizes the downtime involved in replacing seals. 

Let’s take a quick look at the most common materials used in making seals:

Qualities of Hydraulic Seal Materials

CRC Distribution Is The Place for Seals

CRC Distribution carries a complete line of seals in a variety of materials. Our engineers are also capable of matching custom seals for virtually any application. More importantly, our personnel are experts in helping you determine the best custom seal solution for your application. Just a few industries where we can apply our sealing expertise include:

Contact us at 866-916-3998 or email us at sales@crconline.com. You can also visit our website.