A rigid coupling is a type of shaft coupling used to connect two shafts at their ends to transmit power. In the case of these couplings, the shafts provide a fixed union where torsional flexibility is not required, shaft alignment is maintained, and proper bearing support is provided. To reduce shaft deflection shaft support bearing should be located as close to the coupling as possible. Large couplings and those running at high speed may require balancing to reduce vibration. However, they are simple enough to install.
You will get efficient and thoughtful service from CNG.
Flange couplings are used to connect shafts of the same or different diameters. The device consists of 2 flanged hubs, bored and keyed to fit their respective shafts and joined by bolts. Some have removable bushings for easier replacement. The couplings usually are made of carbon steel and are available to be over 8” in diameter. The flange-style couplings are primarily designed for heavy-duty applications.
Rigid Flange Coupling by Ringfeder
Sleeve couplings are made from one piece of material; factory bored to accommodate standard shafting. Keyways are broached, and set screws are installed. Shaft keys transmit torque from the shaft to the coupling hubs, and set screws keep the coupling from sliding along the shaft. Sleeve couplings are also made in clamping style. Clamping styles come in two ways: one-piece design and split, two-piece. Split, two-piece couplers can be installed and removed without machine disassembly.
One-piece Sleeve Coupling
Ribbed couplings may be used for heavy-duty services, made of 2 pieces and used to connect shafts of the same diameter. The coupling is keyed to both shafts with bolts. Those permit quick and easy installation and removal.
Ribbed Coupling from TB Woods
In summary, the benefits of rigid couplings include their low price, high torque capacity, torsional stiffness, and zero backlashes.
In the end, we would like you to watch a short demo video below about flange couplings made by RINGFEDER.
Check our article Gear Couplings: Benefits and Applications.
Feel free to Contact Us if you have any questions, need more information or if you are interested in purchasing a coupling.
HVH Industrial Solutions is an authorized distributor of the following coupling manufacturers: Ringfeder, System Components, TB Wood’s, Ameridrives, Bibby Turboflex, and Guardian Couplings.
We work closely with the engineering teams of the above companies to provide superior customer service and engineering support.
Grooved pipe couplings are some of the most important equipment in fire protection, allowing quick and water-tight connections without pipe threads, flanges, or welding. Instead, installers simply butt the ends of pipes together and seal them with a gasket and clamp.
But there are also two kinds of grooved couplings that serve different purposes. Rigid grooved couplings don’t allow much movement and serve as a standard pipe joint. But for situations where some give is needed—specifically, seismic protection of fire sprinkler systems—flexible grooved couplings are the solution.
This article reviews the basics of grooved pipe couplings and details the differences between a rigid and flexible coupling. We also explain when and how NFPA 13: Standard for the Installation of Fire Sprinkler Systems ( edition) requires using flexible couplings for seismic protection.
Shop our selection of rigid grooved couplings and other fittings for your pipe-joining needs. Looking for flexible couplings? Contact QRFS today for a quote or to place a special order.
Grooved couplings are the fastest way to join pipes. And the technology is simple. Earnest Tribe, the founder of Victaulic, patented the grooved pipe joint in after developing the tech to meet wartime needs. Grooved couplings avoid the need for welding or other joint types. Instead, they use three components: 1) pipe with grooved ends, 2) synthetic rubber gaskets, and 3) c-shaped clamps.
To form a joint, installers butt two pipes with grooves cut in the ends together. A lubricated gasket slips over the pipe ends so that it overlaps the joint. And a c-shaped clamp or housing fits into the grooves of the pipe, compressing and stabilizing the gasket. This video from Victaulic shows how the joints are made:
But as we mentioned, there are two kinds of grooved joints. So, what’s the difference between a rigid and flexible coupling?
From the outside, you can’t look at a grooved coupling and know whether it’s rigid or flexible; they look the same. The difference is on the inside of the joint in the way that the gasket, groove, and clamp fit together. A rigid clamp permits next to no separation, rotation, or angular movement. But a flexible coupling permits some movement and space without compromising the seal or damaging the pipe. NFPA 13 officially describes how much flexibility is allowed:
3.3.83 Flexible Coupling. A listed coupling or fitting that allows axial displacement, rotation, and at least 1 degree of angular movement of the pipe without inducing harm on the pipe. For pipe diameters of 8 in. (200 mm) and larger, the angular movement is permitted to be less than 1 degree but not less than 0.5 degree.
Key to this definition is the term “listed.” A testing laboratory such as UL or FM Global must verify that a flexible grooved fitting meets specific flexibility, seal, and strength requirements before it can be used in a fire sprinkler system.
This diagram from Bentley Communities helps illustrate the physical difference between the two types of joints:
Almost all grooved couplings use rigid joints because rigid, unmoving joints are desired for most situations. But flexible couplings, while less common, do play essential roles in seismic protection for fire sprinkler systems that require an earthquake-resistant design.
Some fire sprinkler systems require design measures to protect them from earthquake damage. In our overview of the principles of seismic protection, we explain the two basic techniques for protecting pipes from damage: adding rigidity and adding flexibility. Rigidity, in the form of seismic bracing, ensures that pipe moves with a building in an earthquake instead of shaking violently and breaking loose.
Flexibility, on the other hand, prevents damage to pipes caused by differential movement. When an earthquake’s powerful p-waves shake a building, the whole structure can move—but not always all at the same time. For example, the ground floor moves first in tall buildings, and the top floors lag behind. This wave-like motion that resembles a slinky is called “story displacement.” And the differential movement it causes in various onsite equipment can snap fire sprinkler pipes.
The solution to this problem is flexibility, which designers can achieve with flexible grooved couplings. The modest ‘give’ allowed by these devices can prevent pipes from being damaged in an earthquake.
NFPA 13 requires grooved flexible couplings for pipes that are 2 ½” or larger (Section 18.2.1) in certain buildings that fall into specific design categories (SDC). And because story displacement significantly affects risers, most of these rules involve risers (18.2.3.1):
Within 2 feet of the top and bottom of each riser, with some exceptions for short risers
Within 1 foot above each floor in multistory buildings (except roofs)
Within 2 feet below each floor in multistory buildings
Within 1 foot of concrete or masonry walls, with exceptions made where adequate clearance is provided
Within 2 feet of building expansion joints
Flexible couplings are also required at horizontal tie-ins to the riser (18.2.3.2) and the connection of drop-pipes (18.2.4).
Flexible couplings allow flexibility when two structures move independently. But don’t forget that bracing, which ensures pipe moves with a building, is the other core technique of seismic design. Flexible couplings can work against this objective by reducing rigidity. So, to compensate, NFPA 13 says that flexible couplings should only coincide with structural separations (18.2.2). And where they are used outside the explicit instructions, extra sway braces are needed (18.2.3).
In our previous blogs, you can learn more about the principles of sway bracing and how cable sway braces work.
Flexible couplings can also be used to construct seismic separation assemblies. These pipe assemblies are used where horizontal pipe must cross an engineered gap, called a seismic joint, between two structures.
The “structures” can be two independent buildings or two freestanding wings of the same building. When a pipe crosses a gap like this, NFPA 13 requires seismic separation assemblies (18.3.1) to keep it from breaking when the two structures move during an earthquake.
There are two ways to build a seismic separation assembly (18.3.2). One approach uses flexible pipe arranged in a u-bend. The other involves a zig-zag pattern of flexible grooved elbows. Either way, the assembly should accommodate a wide range of motion in three directions: the complete closing of the gap between the structures, a doubling of the gap, or lateral movement equal to the size of the gap.
You need a stiff joint for the vast majority of sprinkler pipe connections. That’s why most grooved pipe joints use rigid couplings. But sometimes, flexibility is necessary for seismic design, and the extra range of motion provided by flexible couplings can prevent earthquake damage.
Be sure to check your local codes, including whether a building falls within a seismic design category (SDC) that requires special equipment to keep fire protection systems safe. A qualified system designer must make this determination. Regardless of what you need, QRFS can provide:
Rigid grooved couplings and pipe fittings — in stock and online.
Flexible couplings on request; contact us today to place a special order.
If you have questions or need help finding the part you need, call us at (888) 361- or .
This blog was originally posted at blog.qrfs.com. If this article helped you, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.
There are two main types of couplings: rigid couplings, which connect two shafts with a solid and high-precision hold, and flexible couplings, which can be used to connect slightly misaligned shafts but which can’t provide the same level of torque transfer. While both coupling types have their advantages and disadvantages, it’s important to know which coupling to choose in a particular application.
How Do Rigid Couplings and Flexible Couplings Differ?
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Ultimately, the key difference between rigid and flexible couplings is in the connection they provide. Rigid couplings provide a rigid connection; the two shafts are firmly connected, and the coupling allows for a smooth transmission of torque throughout the system. Flexible couplings create flexible connections, and the components can lose some of the torque power through the interaction. While metallic flexible couplings offer greater torque capability than other flexible couplings, some torque is still lost.
Other important differences between rigid and flexible couplings are:
Alignment Requirements:
Flexible couplings can handle slightly misaligned shafts. Rigid couplings are torsionally stiff and can’t tolerate any misalignment. This applies to both shafts that are physically misaligned at rest and parts that may cause misalignment during operation due to thermal changes.
Backlash:
Rigid couplings, especially newer models of aluminum rigid couplings, can significantly reduce backlash to at-zero or near-zero levels. Flexible couplings don’t offer the same protection.
Maintenance Requirements:
Because rigid couplings are stiff, they do not absorb vibrations, which can lead to early wear on parts that aren’t properly aligned. Operators should routinely check rigid couplings for wear and alignment, and they should also routinely apply lubricant. Flexible couplings can handle vibration and shock without adverse wear.
Complexity:
Flexible couplings often have more components and/or are more complex. This can make operation and maintenance more complicated. Rigid couplings are more simple and straightforward in comparison.
Applications:
Flexible couplings can be used in servos with low or moderate torque levels and the potential for shaft misalignment. This includes applications such as machining tools, semiconductor manufacturing, and packaging equipment. Rigid couplings work best for high-torque requirements, shaft support applications, and push-pull use cases.
Cost:
Rigid couplings are more affordable than flexible couplings, which tend to have a high cost.
Advantages of Rigid Couplings
Both rigid and flexible couplings have their place in almost any complex motion system. However, rigid couplings provide several advantages over their flexible alternatives that make them the preferred choice for many projects. Some of their key advantages include:
Excellent torque transmission: Rigid couplings can efficiently transfer torque from one shaft to the other connected shaft.
Low cost of production: Manufacturers can produce standard and custom rigid couplings at cost-effective rates.
Precision, with nearly zero windup and zero backlash
Torsional stiffness: High torsional stiffness allows for better positioning.
Simplicity
Alignment capabilities: Rigid couplings can be used to establish shaft alignment between the motor and connected components.
Suitability for push-pull and support applications
Easy assembly, disassembly, and maintenance operations throughout the life of the coupling
High-Quality Rigid Couplings From Stafford Manufacturing
Rigid couplings provide excellent torque, minimal backlash (with some of our standard couplings providing zero backlash), and high torsional stiffness. This makes them ideal for a wide variety of precision applications that need high levels of power. At Stafford Manufacturing, we manufacture and supply our clients with high-quality rigid couplings for a range of applications. Learn more about how to choose the right rigid coupling for your needs, or browse our catalog to find the right products today.
Couplings fall in two main categories: rigid couplings and flexible couplings. In this post, we are going to make a comparison of the main differences between the rigid and flexible couplings.
These types of couplings provide a solid connection between two shafts, high precision and torque, but without misalignment absorption capabilities; it allows no movement between the two shafts and they require lubrication in many times. They cannot absorb vibrations, both shafts should be perfectly aligned to ensure a good performance and avoid damping transmission and possible breaks in the installation.
Muff or Sleeve coupling
Flange coupling
Clamp coupling
Rigid coupling Muff coupling
In the second main categories of couplings we can also make difference between two categories of flexible couplings: Flexible Metallic Couplings and Flexible Couplings with an Elastic Element.
Flexible Metallic Couplings: The power transmission is totally made by metallic compounds.
Flexible Couplings with Elastic an Element: The power transmission is made by an elastic element placed between either hubs or flanges.
They compensate misalignments, movement or deflection. They are very useful when having quick and short starts. Normally they provide less torque transfer, but they have a high capacity to accommodate axial, parallel and angular misalignments, as well as reducing transmission of shock loads or vibration.
In case of the flexible couplings, they normally provide less torque transfer comparing with the rigid couplings, simply considering that these, are made of a piece of solid metal. However, we can obtain a wide range of torque capacity depending on the type of flexible coupling (having a higher torque capacity in metallic flexible couplings than in couplings with flexible element).
Flexible Metallic Couplings:
Gear Coupling
Disc Coupling or diaphragm Coupling (LAMAFLEX COUPLING)
Chain Coupling
Grid Coupling
Image of Lamaflex disc couplingFlexible Couplings with Elastic Element :
Tyre coupling (UNEFLEX)
Spider or Jaw coupling (ACOFLEX)
Bush Pin type coupling
Image of UNEFLEX highly rubber flexible couplingImage of ACOFLEX spider coupling
It is relevant to know each coupling type’s features when we are planning to make an installation.
Want more information on Flexible Grooved Coupling? Feel free to contact us.