What's the Difference Between Static and Dynamic Hydraulic Seals?

The first decision you have to make when you choose hydraulic seals is whether to buy static or dynamic products. While these seals both do the exact same job, they should be used in different applications.

What do you need to know about static and dynamic seals?

What Are Static Hydraulic Seals?

Static hydraulic seals create seals between two parts that do not move. So, for example, you might use these seals as o-rings or back-up seals on pipes and flanges. Here, you simply need to get a tight seal on the surface.

These seals usually sit in a grooved space between their two parts. They create a fixed and unmoving seal. However, this doesn't mean that they can't sometimes change shape.

If seals sit on a pressurised system, then they have to deal with changing pressure levels. The seals' parts don't move, but the pressure under them might change.

If seals can't change shape when pressure shifts, then they will break. So, here, seals will expand and contract to change their sealing pressure depending on what is going on in their containment area.

While static seals are used on non-active applications, you do sometimes use them on some dynamic parts. However, the role they play on the part will still be static; they'll seal areas that don't move.

Static seals tend to last longer than dynamic ones. They are subject to less movement, so they don't wear as fast and are less likely to break under stress.

What Are Dynamic Hydraulic Seals?

You use dynamic hydraulic seals on parts that move. Here, you have to create and maintain a tight seal that holds under motion forces. So, for example, you might use these products in connecting areas of a piston/rod system.

It is important to look at the type of movement the seals have to deal with before you choose a product. For example, you need to factor in whether the motion is oscillating, rotational or reciprocating. You then have to choose seals designed to cope with that range of motion.

Because dynamic seals have to move, they don't typically last as long as static products. They can wear or break more quickly; you might need to check their condition and placement more frequently.

For help choosing the right products for your applications, ask hydraulic seal suppliers for advice. They can check whether you need active or dynamic seals. They can also help you choose the right materials.