In the sealing industry, the most basic solution is quite often the best way forward. If a problem can be solved with a standard dimension o-ring, that should be the route taken.
Sometimes, however, an o-ring will not resolve the underlying sealing problem, or application factors prevent an o-ring solution.
For example, an o-ring is not an ideal solution for most dynamic applications due to its round profile and natural tendency to roll (as round shapes are want to do). In these cases, an option that has the same advantages of standard sizes and availability is a quad-ring. Its clover leaf shape of four equal lobes provides the stability in the gland to resolve some of the world’s most demanding dynamic applications, and has the benefit of a design that can utilize the same gland dimensions of standard o-rings in many cases.
Quad-Rings for Linear Applications
The two main types of dynamic movement are linear and rotary. In the case of a linear application, such as a cylinder, a moving component travels along an axis with a seal riding on the inside of a bore or the outside of a shaft. An o-ring can work in this type of application, but without proper lubrication at all times, the o-ring can bind and begin to twist upon itself, potentially leading to a spiral failure. The seal wraps up within its own cross section until the material fails and creates a leak path. A quad-ring, with its four equally sized lobes, forms a square shape with two sealing points rather than an o-ring’s one contact point. This creates stability in the groove so the seal remains static in comparison to its surroundings, and prevents the desire of the seal to bind and roll with the dynamic mating surface. It also can allow for a slightly rougher sealing surface due to reduced concern for rolling when the mating surface is in motion.
Quad-Rings for Rotary Applications
In the case of rotary motion, a quad-ring is surprisingly adept at sealing a wide range of speeds and pressures. The Parker O-ring Handbook does provide gland dimensions and guidance for use of o-rings as rotary shaft seals under conditions up to 1500 feet per minute and over 800 psi, but similar concerns with the o-ring stability can arise. Quad-ring rotary designs provide the same two points of contact for sealing and gland stability found in static and linear dynamic design profiles, while allowing for standard sealing at up to 900 feet per minute and 750 psi. One of the driving benefits of a quad-ring over an o-ring for a rotary seal is the two points of sealing contact. The cross section sizes for both types of seals are the same, but the two points on a quad-ring require a different style of groove, which allows for a smaller overall sealing package. While a rotary o-ring still requires at least some amount of stretch over the shaft, quad-ring design guidelines use the housing or bore to squeeze the quad-ring seal down to a shaft size that is several thousandths of an inch smaller than the free inside diameter of the seal. This is done to ensure the quad-ring remains static in the groove and the dynamic motion occurs on the ID of the seal as intended, allowing for a rougher surface finish in the groove than is required on the shaft.
Quad-Rings: A Robust Solution
Quad-rings can work in many areas where an o-ring is not quite robust enough of a solution. Their unique design affords a level of stability that allows for use in dynamic applications where an o-ring can struggle. While an o-ring is often the first thought when sealing is concerned, the lesser known quad-ring can become the hero when an application demands more from the sealing solution. Movement demands stability and when it comes to basic seal geometries, few can match the robust stability of a quad-ring seal.