Determining the Best Way to Prevent Flexible Hosing Leaks

The selection of the proper fittings and hose clamps for cold plates and heat exchangers is critical to a reliable liquid cooling system. It can prevent unnecessary downtime and equipment damage. Based on over 50 years experience with scores of fittings and clamps in hundreds of applications, we have found two options which have proved to be superior. Below we discuss the use of beaded fittings and the advantages and disadvantages of the two preferred clamp options.

When a system requires flexible tubing, the beaded tube fitting has been specified almost universally, especially in critical applications such as computer, medical, laser and automotive where operation must be 100% leak free. The bead, a 0.035" +/-0.003" ridge for 0.375" OD tubing (See Figure 1), prevents the clamp and hose from slipping off the tube; the bead does not prevent leaks, however.

The clamp prevents leaks at the joints. The clamp sealing performance, defined as the static pressure and tightness, depends on several factors:

• The material and design of the hose
• The compatibility of the hose bore to the connecting part
• The correct selection and installation of the clamp
• Various mechanical factors such as pressure, temperature, and vibration

Aavid recommends two types of clamps, the ear/crimp clamp and the worm or gear clamp. The ear clamp, shown below in Figure 2, is a metal band that is crimped with a special tool to form a leak-free connection. The worm clamp, Figure 3, consists of a notched band with a screw mechanism to loosen or tighten the clamp.





Each clamp has advantages and disadvantages as determined by your application. See Table 1 for a comparison of features.

Table 1: Clamp Comparisons of Features

Ear Clamp	Worm Gear Clamp
Superior clamping performance	Standard clamping performance
Circular, uniform clamping pressure	Some have flat spot under tightening mechanism
Shows tampering	Does not show tampering
Not reusable	Reusable
Special tool required for installation; hand tool or pneumatic tool (recommended)	Standard screwdriver required for installation
Can be difficult to install (crimp) in tight places	Can be installed in tight places

Ear Clamps

Ear clamps provide superior sealing because the connection cannot loosen over time. Since ear clamps have a low spring constant, Hooke's Law dictates that ear clamps maintain a greater force after hose relaxation. They maintain a circular geometry after tightening which proves more reliable. Installation is simple, the ear clamp slips over the hose fitting joint and requires a pneumatic or hand tool to tighten. We strongly recommend the pneumatic tool because it insures consistent pressure applied around the fitting and greater consistency in a production environment. Also any tampering is visible with the ear clamp.

The drawback of the ear clamp is that it can only be used one time and it requires a crimping tool for field replacement. The crimping tool can be bulky and difficult to use in tight places. These three disadvantages limit the ear clamp's serviceability.

Worm Clamps

The worm clamp has its own set of issues. Some designs have a flat spot below the screw mechanism that can result in uneven pressure around the fitting. However, many worm clamp vendors have new designs that eliminate the flat spot. In addition, worm clamps tend to be stiff so a slight hose relaxation can result in a significant loss of force. In the past the notches for the screw mechanism would cut into the hose and could be a potential leak source. Again, new designs include a smooth inner surface.

The chief advantage is greater system flexibility and serviceability. The worm clamp is easily replaced in the field with just a screwdriver. And thanks to its wide diameter range, the same clamp can be used with a variety of hose sizes. The correct choice of materials and the availability of many band sizes make the worm clamp ideal for low and medium pressure applications.

Hose Clamp Selection Conclusions

Let your performance requirement guide you. In the end, the best fitting/clamp combination will be determined by your performance goals. If leak integrity is paramount and high cooling liquid pressures are involved, the ear clamp is appropriate in most cases. When easy field maintenance is the key factor and liquid coolant pressures are low to medium, the worm clamp/beaded fitting combination will serve you best. If you still have questions about your specific application, consult your clamp manufacturer. With the proper fitting and clamp, your liquid cooling loop will provide years of leak-free operation.