How Constant Tension Hose Clamps Counteract Cold Flow
If you’ve ever clamped a hose or pipe, you know it’s not as simple as set it and forget it. You want the clamp to compress the hose around the fitting to ensure a tight seal, but that compression can deform the hose and lessen the effectiveness of the seal.
After you install a clamp, the material of the hose actually moves out from under the clamp to escape the pressure. This movement, known as cold flow, means that over time, the seal the clamp provides will not be as tight as it was when you installed it. This is so even if the hose isn’t in regular use and nothing in the environment changes.
But add in the expansions and contractions of the materials caused by temperature changes, plus the changes in pressure resulting from normal use, and the cold flow process accelerates. The endpoint of cold flow is the condition of the compression set, where the hose has permanently deformed to the size of the clamp.
The Right Clamp Can Counteract Cold Flow
Certain materials are more prone to cold flow issues. It’s seen more with thinner-walled, less rigid hose materials, most notably silicon. Materials engineers have made changes to the design of silicon hoses over the years, but cold flow still occurs, so it’s essential to choose the right clamp to address the potential problems.
You need a clamp that allows for expansion and contraction. Otherwise, you’ll have a situation in which the hose won’t give as the pressure and temperature change, leading to a bulging hose and a more extreme compression set. Your best bet is a constant tension clamp (also called a constant torque clamp), which has been designed to operate in cycles of expansion and contraction.
The two most common types are the constant tension band clamp and the constant tension spring clamp. These both tend to be robust clamps that allow you to generate high sealing force or band load. But tightening the clamp does only so much when the side inside of the clamp is smooth; it doesn’t bite down well on the equally smooth material of the hose.
The Case Of Automotive Hose Clamps
Silicon hoses are common in automotive installations, and constant tension clamps are fine for many of these uses: Exhaust systems often use band clamps, for instance. But in high-performance installations, something more is needed.
Tight, reliable seals are essential for the safe operation of the family car, but they’re even more essential in the more demanding conditions of a race car. In turbo-powered engines, a clamp failure can cause loss of boost, or even hose blow-off, which could be extremely hazardous if the car is operating at a high speed.
To counteract that danger, the engineers at Murray Corporation have further refined the design of the constant tension band clamp. They have created a turbo seal constant tension clamp with a convoluted band, and a dual bead shield that bites down on the hose material even at lower temperatures. It, therefore, requires less tightening than a T-bolt clamp to generate a good seal. This unique Dual Bead Shield® design is proven to remain in place even under the high-stress engine conditions of a race car.
No clamp can just be installed and ignored – not even a constant-tension clamp. Once you’ve chosen the right clamp and installed it, you still need to check it regularly and tighten it as needed to make sure that it continues to provide the tight seal that will prevent problems.
