Think for a moment about this incongruity: the watertight integrity of a vessel often relies on something as simple and mundane as a hose clamp, some of which cost less than a dollar. While I cant say Ive seen many vessels sink or suffer major flooding as a result of a failed hose clamp, Ive seen enough to know its something I wish to avoid.
Then, there are all the other important hoses that hose clamps secure, from fuel fill and supply plumbing to sanitation and potable water systems. Clamps that fail or are improperly used in these applications can lead to a host of failures that range from inconvenient to catastrophic. Thus, theres little doubt that this small component plays a big role in your vessels reliability.
Hose clamps dont operate on their own; in order to form an effective hose seal, its important that they and the hose be used in conjunction with compatible, purpose-made pipe-to-hose adapters. On far too many occasions, one nearly life threatening (more on that next month), Ive seen hose connections fail because the hose was installed over a pipe fitting that was not specifically designed to support a clamped-in-place hose.
HOSE CLAMP BASICS
The worm gear clamp has been around since just after WWI when its inventor, Commander Lumley Robinson, a retired Royal Navy officer, patented the first design in 1921. He called it a Jubilee Clip, a name that remains familiar to many Britons (as well as those who have worked on British automobiles). L Robinson and Company, along with many other manufacturers, continues to manufacture this venerable product to this day.
The ubiquitous hose clamp, relying on a simple screw and threaded band arrangement, is extremely effective at providing uniform pressure to hoses and the fittings over which they are placed. However, as respected as the original design may be, it isnt without its flaws. Primary among these is the fact that many hose clamps rely on a series of perforations that are cut into the band to form the screw threads. These perforations eliminate a significant portion of the bands cross section, weakening it, and allowing it to elongate when tensioned. The elongation leads to micro cracking, which in turn provides a toehold for stainless steel crevice corrosion, a form of metal decay that is peculiar to this alloy. When hose clamps part they nearly always do so across one of these perforations, either as a result of overstress or corrosion, or a combination of both. Additionally, the typical band itself is comparatively thin, which makes it relatively easy to strip the thread if the screw is over tightened.
The typical hose clamp, what I refer to as an automotive clamp, is made of either a stainless steel or galvanized steel band (most clamps sold in the United States utilize stainless steel bands) with a plated mild steel screw. In an automotive environment, depending upon the level of humidity, water, and salt exposure, these clamps can be expected to last for 10 or 20 years. However, in a marine environment, the plated screw and galvanized band quickly come to grief and, as such, this style of clamp should never be used in a marine application. Up-rated marine models with stainless bands and screws are available and represent a huge improvement over the automotive version; however, because they retain perforations and scant band thickness, they, too, remain prone to elongation, crevice corrosion, and stripping. In short, while they are better than the automotive variety, there exists yet a better mousetrap.
HOSE CLAMPS READY FOR SEA
Solid band, all-stainless steel hose clamps represent a significant leap in both quality and reliability over both automotive and standard marine clamps. This style of clamp eliminates the band perforations, replacing them with embossed, rather than perforated threads, necessitating a thicker band, which resists elongation, cracking, and stripping. Solid band clamps are virtually immune from stripping even when over tightened.
These clamps are available from several manufacturers, including Robinsons Jubilee incidentally, in a wide variety of size ranges. Importantly, while all-stainless steel construction is a prerequisite for true marine clamps, clamps are often available in either 304 or 316 alloy, with a consequent difference in cost. For the most part, unless the clamp will be routinely submerged or exposed to water or spray, 304 alloy clamps will work well and cost the user less. In cases where maximum corrosion resistance is required, for stuffing box hoses for instance, then the added cost of 316 alloy clamps is easily justified.
For especially large diameter or particularly stiff or thick hose, a slightly different variation on the traditional worm gear clamp may be required. T-bolt clamps utilize a conventional threaded machine screw-type fastener coupled with the traditional hose clamps band. The result is a clamp that is capable of imparting a higher level of compression over a wider surface area (T-bolt clamps are typically wider than most traditional hose clamps).
As useful and rugged as T-bolt clamps are, they possess their own weaknesses. Because they rely on a stainless steel stud and a stainless steel nut, they are prone to thread galling. Thread galling is common to all stainless steel fastener applications, it essentially amounts to micro welding as a result of heat generation within the threads as they are being tightened. This is easily prevented by lightly lubricating the threads before clamps are installed (if this hasnt already been done by the manufacturer).
Another Achilles heel that these clamps possess is a function of the manner in which they are made. The T-bolt is retained by the band by folding the latter over and spot welding it to itself, creating an envelope of sorts. While this makes for a resilient retention method for the T-bolt, it also forms an area where water can be trapped, which often leads to crevice corrosion. If routinely used in wet locations, such as shaft and rudder stuffing boxes, bilge pump plumbing, etc., they are prone to crevice corrosion-induced failure.
Because necessity is the mother of invention, a manufacturer named AWAB www.awabllc.com (they also manufacture high-quality, solid band hose clamps in 304 and 316, as well) has created a T-bolt clamp that uses interlocking, rather than folded and spot-welded bands, virtually eliminating the water-trapping fold and the corrosion to which it so often leads. These clamps are well suited to wet locations without concern for such failures.
When it comes to hose clamp selection, dont skimp on this ultra-important component. Clamps must be all stainless steel, 304 for dry applications, and 316 for wet, with solid, embossed thread bands.
Next month Ill discuss hose clamp installation, pipe-to-hose adapter dos and donts, and how an improperly installed hose nearly resulted in serious injury for the author.