By Marcia Sampson
Summary: Here water treatment dealers are invited to look at flexible tubing in a whole new light, where a discussion comparing the differences between single-barb and multiple-barb fittings takes center stage.
Advances in polymer chemistry over the past two decades have resulted in improved formulations for tubing that have increased its flexibility and elasticity as well as making it an ideal, safe choice for potable water treatment applications.
The excellent flexibility and elasticity exhibited by modern polyethylene, polyurethane and PVC tubing formulations provide a number of benefits for system designers and installers including:
- Tight radius bends can be negotiated without kinking or flow restriction,
- Design layout is simplified because bends and turns are made in the tubing and not with connectors (in rigid tubing designs, additional connectors are required at each turn point, which increases the complexity of the system),
- Flexible NSF Standards 61 and 51 certified tubing is widely available in sizes and configurations to meet almost any requirement,
- A superior seal results when flexible tubing is coupled with single-barb fittings, and
- Single-barb fittings take full advantage of flexible tubing’s elastic memory properties to virtually eliminate the need for clamps in many situations (see below).
The single barb is closer to a radial O-ring engagement between the elastomer tubing and the more rigid plastic, which allows the elastomer to relax behind the barb more snugly.
With the introduction of Standard 61 certified tubing and NSF certified single-barb connectors (see Figure 1), the possibilities are greatly expanded for creating compact systems that fit comfortably within confined areas. With the installation of rigid tubing and push-on connectors in these areas, a primary concern is the potential for leaks resulting from misalignment and lateral stress at the connector. This isn’t a concern with flexible tubing/single-barb connector designs. In addition, there’s a tendency for rigid tubing to transmit water hammer, expansion and vibration forces to the point of connection. In a large installation, the rigid tubing will absorb some of this stress. In an installation with shorter runs of tubing, however, almost all of the vibration is transferred. In a flexible tubing installation, stress and vibration are dampened and absorbed by the tubing regardless of the length of tubing used. This often results in much quieter operation and increased reliability for the entire system.
Single-barb connectors are an essential component in building systems using flexible tubing. They offer both safety and mechanical advantages when compared with multiple-barbed fittings (see Figure 2). With a single-barb fitting design, it’s possible to manufacture a barb without a mold parting line. This is essentially impractical with multiple-barb designs. Parting lines can be a source of leaks in a connection and provide a pathway for bacterial or fungal migration.
Multiple-barb fittings manufactured with worn or misaligned mold sections are the most common source of excessive mold parting lines. Make certain that the single-barb fittings you choose don’t have a parting line on the barb surface. It requires an extra step in the molding process to produce this type of barb, but the benefits far outweigh the small additional cost. An additional advantage of the single-barb fitting design is its ability to offer better sealing than multiple-barb fittings. A single-barb design uses a straight or slightly tapered shaft behind the barb with a diameter close to the original tubing interior diameter. This allows the flexible tubing to relax to its original shape behind the barb, creating a tight seal with the barb’s outer radius. Some designs incorporate the straight surface behind the barb to provide an anti-rotation device that prevents the tube from rotating around the shaft and wearing the seal. In contrast, multiple barbs cause a bridging effect that doesn’t allow for full relaxation of the tubing behind the individual barbs. This bridging effect can result in less overall tube-to-barb contact and may cause leak paths, creating dead space between the barbs where microbiological pests can accumulate.
The perceptions of many people regarding tubing and barbed-fitting combinations are based on their experience with semi-rigid polyethylene tubing and multiple-barb connectors of the type commonly used in lawn irrigation systems. These components, designed for non-critical applications, cut a system’s cost but are prone to leaks and pressure blowout. Because of weak elastic memory, semi-rigid tubing exacerbates problems inherent in systems designed with multiple-barb fittings and often necessitates extreme clamping pressure to prevent leakage and blowout. Instead, designs utilizing flexible tubing with single-barb connectors have a proven record of consistent reliability over many years in medical device, pharmaceutical and chemical industry applications (see Figure 3). The utility of flexible tubing and single-barb fitting combinations has furthered their acceptance in a growing number of applications including the reverse osmosis and water conditioning industries where they have seen a steady increase.
Current economic conditions have led to a renewed focus on bottom-line costs as companies are forced to operate in increasingly competitive markets. Employing flexible tubing and single-barb fittings is an easy way to reduce system costs in many water applications. Single-barb fittings are easy to install and generally cost less than push-on or compression-type fittings. Economic benefits are further enhanced because the turns and bends made with flexible tubing reduce the number of connections required. Resulting significant savings in material and labor costs are achieved with no compromise in the quality and reliability of the system.
About the author
Marcia Sampson is co-founder and CEO of Eldon James Corp., of Loveland, Colo. She has been involved in the production of plastic hose fittings for more than 15 years. Her father, Kent Sampson, was a pioneer in the development of single-barb fittings for use in medical systems and invented the Kent Quick Disconnect System. She can be reached at (970) 667-2728, (970) 667-3204 (fax) or email: email@example.com