
Many times
hose clamps display leaks even after the application of sufficient installation torque & people are tired of finding out the root cause of this issue & end up with excess tightening of the clamp as a solution. Today in this article I will shed some light on a much unknown & a topic on which we hold our tongue very often, the root of these unknown leaks- the Cold Flow or the Cold Leaks…
1. Cold Leaks -
The hose which is the prime entity of our story is made of elastomer (rubber) which has a bad habit of deformation and is expressed in a term called Compression set (C-set). Compression set is the measurement of how well a material can revert back to its natural shape after being compressed by a load. A material which returns near its original thickness is said to have an ideal compressive strength.
When a hose clamp is tightened on a hose it seeks to reproduce the type of indent (impression) similar to the clamp band which is tightened on the hose. After the introduction of the torque, the clamp is now tightened in one shot & the hose now is not given sufficient time to get into action (rebound) so now with time, the hose compound will slowly move out from under the clamp band to the region of less band force to relax itself. The so called flow of hose can be simulated with a help of a frugal method depicted in fig-1 below wherein a clay is kept under the hose clamp & tightened to installation torque. The clay flows out from the clamp band to the region of no load.
Figure 1- Clay wrapped under the hose clamp before introduction of installation torque
Figure 2-An Exaggarated Frugal Simulation of Hose flowing under the clamp band with the help of clay
This relaxation of the hose is perceived as a drop in the installation torque which results in lower band tension force which subsequently leads to leakage & slippage of the joint. This drop in the installation torque can be easily determined using the Relaxation tests. To minimize these relaxation losses, the
Dual-step tightening process should be adapted so that the hose can have some time to relax itself before the complete delivery of the torque so that the lost torque can be quickly replaced by the new torque which is being currently applied. Truly speaking, manual tightening of clamps is the best way to fix this issue. If manual torquing is not possible at all joints at least the joints demanding critical applications should be turned manually.