Are constant tension hose clamps effective?

Our tests show that JCS's Hi-Torque hose clamps outperform industry-standard constant tension hose clamps.

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We are sometimes asked by clients how our hose clamps compare with constant tension hose clamps ' a different design of hose clamp to the hi-grip and hi-torque worm drive clamps we manufacture at JCS.

Design flaw

The idea behind constant tension clamps is that during tightening, the Belleville washers compress and act like a spring. When the rubber relaxes, the spring action pulls the band through the housing, making the clamp smaller to compensate for shrinkage in the rubber hose.

However, we believe the basic engineering principles underpinning this design are flawed.

The idea that a spring can modulate the amount of pressure a clamp exerts over time and under a range of extreme environmental conditions just doesn't hold water ' in some cases literally! In effect you are putting a spring in a pressure system, and when the pressure of the fluid exceeds the spring tension you have a leak.

There is no substitute

In our extensive experience, there is no substitute for clamps that are made to the highest quality and strength, combined with innovations such as JCS's 'straight line' housing ' which ensures that every thread of the screw is fully engaged with the band to provide more torque.

We are constantly running tests at our workshop and we recently carried out a number of laboratory assessments on a sample of industry-leading constant tension hose clamps as well as our own clamps to compare how the different designs perform'

Tests prove conclusive

We tested six constant tension hose clamps of different sizes made by a respected clamp manufacturer from the USA. These manufacturers claim that Belleville washers enable the clamps to cope with 'fluctuating and extreme temperature applications and thermal compensation'.

We ran a number of tests recording at intervals the grip of each clamp on a calibrated test rig to measure the clamping force. These included a 24-hour rubber cold flow test, and a test where the assembly was heated to 125°c for five hours. Both types of clamp were then tested on a hydraulic pressure tester after the cold flow and heat cycle.

In addition, our test professional performed a salt spray corrosion-resistance test, where the clamps were bombarded with salt water. While the JCS clamps remained unaffected, we found rust forming on the constant tension screw in under 24 hours.

The tests also revealed what we'd known all along ' that the constant tension ability of the clamps is quite limited and the capacity of the springs to compress can be a liability.  On most tests, under identical conditions, our conventional HTM clamp substantially out-performed the Belleville design.

We would be happy to share the finer details of these tests with anyone who would like to know more. Please contact us on or

For more helical preformed tension clampinformation, please contact us. We will provide professional answers.

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.

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