Types of Hydraulic Seals |O ring, Quad ring, V ring, U ring, Composite Seal

Leakage from a hydraulic system can be a major problem leading to loss if efficiency, increased power usage, temperature rise, environmental damage, and safety hazard.
Minor internal leakage can be of little consequence and may even be deliberately introduced to provide lubrication of moving parts but increasing clearances may result in pressure drops and slowing down work. Internal leakage does not lead to fluid loss because eventually fluid is returned to the reservoir.
External leakage, on the other hand, is always serious. The principal cause of external leakage is improper installation or sealing failure.

Types of Hydraulic Seals

In this post, we will be studying various types of seals. Seals are classified on the following basis

  1. Bases on sealing (Positive seals and Non-positive seals)
    Positive seals do not allow any leakage what-so-ever it may be (Internal or External) whereas non-positive seals permit a small amount of internal leakage.
  2. Based on applications (Static seals and Dynamic seals)
    Static seals are used to seal two mating parts that have no relative motion between them. Whereas the dynamic seals are assembled between mating parts that move relative to each other. Hence dynamic seals are subjected to wear.
  3. Based on the shape of seals
    These seals include O rings, Quad ring seals, V packing, Cup packing, U packing, etc.

O rings

The O ring is probably the most used static seal. O rings are made of molded synthetic rubber.
O ring gives very effective sealing at high pressure.
O rings are usually molded from rubber compounds however they can be molded or machined from plastic materials also.
O rings, O ring seal
O ring seal
The O ring is usually fitted into a rectangular groove, also called as gland machined into the components to be sealed.
An O ring consists of an O ring mounted in the gland so that the O ring's cross-section is compressed slightly when the gland is assembled.

Quad ring seals

This is a modified square type cross-section made up from homogeneous synthetic rubber.
Cross Section of Quad Ring Seal
Cross Section of Quad Ring Seal

The quad ring is quite versatile and can be used as a static seal as well for rotary and reciprocating motion. It is shown in the figure.
Dynamic & Static Application of Quad ring seal
As opposed to an O ring, a quad ring seal has a more square cross-sectional shape with rounded corners.
The quad ring seal design offers more stability than the O ring design and practically eliminates the spiraling or twisting that is sometimes encountered with O ring.

V-Ring Seal

Fabricated V-ring packings are capable of holding almost all pressure. V-ring is the part of the packing that does the sealing. It has a cross-section resembling the letter V from which its name is derived.
V-ring seal
V-ring seal

To achieve a seal, the V ding must be installed as part of a packing set or stack, which includes one male adapter, one female adapter, and several V rings.
The male adapter is the first ring on the pressure end of the packing stack and is flat on the one side and wedge-shaped on the other to contain the V of the adjacent V-ring.
The female adapter is the last ring of the stack.

U Ring Seal

The fabricated U packing is also used in various dynamic sealing solutions. U packing is always used with a support ring as shown.
U ring seal
U-ring seal
U packings are balanced packings; it seals on both the outer diameter and inside diameter, and are applied individually, not in stacks like V rings.

Cup Seal


  • Cup packings resemble a cup or deep dish with a hole in the center for mounting. 
  • Cup seals are used exclusively to seal pistons in both low pressure and high pressure hydraulic and pneumatic applications. 
  • They are produced from leather, homogeneous synthetic rubber, and fabric-reinforced synthetic rubber.
  • Cup seal
    Cup seal
  • Although the cup packing lip flares outwards, the rubbing contact is made at the lip only when the fluid pressure is low. 
  • As the fluid pressure increases, the cup heel expands outwards until it contacts the cylinder wall, at which point high-pressure sealing is in effect. 
  • As the pressure loading shifts the sealing line to the cup heel, the lip is actually pulled into the cup and away from the cylinder wall. 
  • On the return stroke when the pressure is relaxed, the heel will shrink slightly, leaving only the lip in contact with the wall, avoiding unnecessary wear at the heel. 
  • For reciprocating pistons, two cups installed back to back in separate glands are required.

Composite seals

These types of seals are a combination of various types and are available in the form of sets. They are designed for special applications. A typical minimum friction seal set commonly used for cylinders shown in the figure.
Composite seal
Composite seal
It consists of five rings one central rubber ring and four adjacent plastic rings. The complete set when assembled acts as a single dynamic seal.
Types of Hydraulic Seals |O ring, Quad ring, V ring, U ring, Composite Seal Types of Hydraulic Seals |O ring, Quad ring, V ring, U ring, Composite Seal Reviewed by Admin on 22:06 Rating: 5

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