Using the correct clamp is vital for hoses’ long-term viability.
Just how much attention does a lonely hose clamp require? As long as it’s made of stainless steel, isn’t one the same as the next? No way, and thoughts like that can sink a boat. The ideal hose clamp transfers the torque applied equally around the circumference of the band — equally being the key word.
The two primary varieties of hose clamp commonly used aboard boats are the worm gear and T-bolt. The worm gear–style clamp consists of a coarsely threaded screw, often tightened by a screwdriver (although a socket may also be used), that engages threads that are either cut or embossed into the clamp’s band.
The less common T-bolt hose clamps typically employ a wider band than a worm-gear clamp. Their tightening mechanism uses a standard threaded stud and nut. Usually, they are installed using a ratchet and socket, and the nut includes a nylon insert to resist vibration, including loosening. These attributes make T-bolt clamps desirable for larger hoses and critical applications such as exhaust systems and raw-water intake hoses.
One of the most important aspects of hose-clamp selection is ensuring that the clamp size is properly matched to the hose that’s being secured. On far too many occasions, oversized or undersized clamps are used in any number of critical applications, from fuel supply plumbing to exhaust systems. If the clamp is too small for a given application — i.e., if the band’s width is too narrow — it may improperly impinge on the hose.
On the other hand, if the clamp is too large for the hose, two problems may result. First, a long, excess section of band will hang off of each clamp. Second, the band’s tightening mechanism may lose efficiency as it reaches the end of its threads. In extreme cases, it may bottom out, fooling the installer into thinking it’s properly tightened when in fact it has run out of useable thread.
So what’s not to like about the rugged T-bolt clamp? It does have two weaknesses. Because the stud and nut are both made of stainless steel, they are prone to galling or thread damage caused by localized friction-induced heating. This can be avoided by torquing the clamp slowly and by adding a small amount of light lubricant to the threads prior to installation. In addition, because T-bolt clamps are manufactured using a folded section of track-welded stainless steel, they are, under certain applications, susceptible to crevice corrosion, which can be caused by water that’s held within the fold. Frequently, this happens when T-bolt clamps are used in applications where they remain wet (e.g., if they sit in bilge water).
All that is required is 35 to 45 inch/pounds of torque for the clamp to be tighten properly. That’s about as much as you can apply with a screwdriver without grunting. Too much can lock up the screw and destroy the hose.
Hoses adjust to pressure and slowly give where it is applied. A 200-pound clamping force can become 140 pounds after a few days – a good reason to regularly check clamp tightness.