Last month I discussed various hose clamp designs, materials, and selection. This month well look at clamp installation, installation tools, and pipe-to-hose adapter dos and don'ts.
Installation: one clamp or two?
Questions regarding hose clamp installation abound. Among the most common is the requirement for double clamps. In fact, there are no requirements of any sort governing hose clamp use in boat building and repair, at least not for recreational diesel-powered vessels. The American Boat and Yacht Councils recommendations call for double clamps in only two locations, fuel fill hoses and exhaust systems (my own guidelines add stuffing boxes to this list). While double clamps are undeniably desirable, in any other location they are optional.
The most common double clamp faux pas involves the use of the second clamp in applications where it is not properly supported. For example, using a second clamp where its pressure cannot bear fully on the pipe-to-hose adapter (more on those in a moment) beneath it is extremely common. This phenomenon is often the result of an overzealous installer who believes or often insists two clamps are mandatory and without them failure is imminent. Thats simply nonsense, and ironically, the actions of such a well-meaning individual may lead to damage to, or a premature failure of the hose over which the clamp is installed.
In locations other than those mentioned above, where they are required for ABYC compliance, and especially if the clamp cannot properly and fully bear on the pipe-to-hose adapter without overlapping of clamps, then only a single, high-quality, solid band clamp should be used. Clamps should be installed so that 1/4 inch of hose is visible between the band and the hose end and approximately 1/4 inch between any two clamps bands. In short, its critically important to confirm the length of the pipe-to-hose adapter under the hose before installing a clamp or clamps.
Im often asked, if twin clamps are used, do the screws need to be installed 180 degrees apart. The fact is, in my experience I dont believe it matters; clamps are designed to impart even pressure on a hose regardless of the position of the screw. If it makes you feel better installing them with this orientation, go for it.
How tight is tight?
Hose clamps should be tightened to their manufacturer rated specification. Yes, most hose clamp manufacturers do provide a torque specification for their clamps, typically in inch pounds. While I dont expect most folks to use a torque wrench for clamp installations, doing so once or twice would give you a feel for just how much tension is required by clamp manufacturers to ensure a positive seal between the hose and pipe-to-hose adapter. Most full-size solid band hose clamps call for 3040 inch pounds of torque, which is easily achieved using a screw driver or proprietary hose clamp installation tool. Over-tightening clamps leads to damage to the clamps threads and damage to the hose and increases the likelihood of crevice corrosion (through microcracking of the clamps band). Clamps often require less tension than is believed, which is why the torque wrench test is beneficial.
I've used the term pipe-to-hose adapter on several occasions. A pipe-to-hose adapter, often abbreviated in the industry as PTH, is a device that looks vaguely like a short length of pipe with one important difference, with a few specific exceptions, the area over which the hose is installed is neither smooth nor threaded. Instead, its made up of a series of barbs, sort of bumps with one ramped and one sharp edge. These barbs ensure that the hose is securely retained when clamped. Often, however, installers will use a pipe nipple instead of a PTH adapter. Pipe nipples have both a smooth and threaded section; however, they do not include barbs. The smooth section provides insufficient grip for the hose and the helical nature of the thread creates a path for fluid leakage. These deficiencies conspire to make the pipe nipple an inappropriate and unreliable method of terminating any hose.
Incidentally, fuel fill and exhaust pipe-to-hose adapters may be smooth, unbarbed surfaces; however, they may not be threaded at the hose interface area, i.e., pipe nipples may not be used. By the way, proprietary hose clamp drivers are among my favorite tools. Their flexible shank makes accessing hard-to-reach clamps easier and the ergonomic handle allows the installer to impart the right amount of torque without straining.
Size it Right
Hose clamps are available in a wide assortment of diameter ranges, and for that reason a pet peeve of mine is clamps that are too large for the application. While an oversized clamp may do the job, it invariably leaves an undesirable legacy in the form of a long, potentially sharp tail that is just lying in wait for an unsuspecting forearm or finger to scrape past. If this occurs in a bilge, under a galley, or head sink, where hands and arms are wont to go, the potential for an injury becoming infected is considerable (all cruisers should have an up-to-date tetanus vaccination, which are typically good for 10 years).
In addition to using the right size clamp for the job, you can go a step further by either slightly bending any remaining tail down into the tensioned portion of the band or by installing one of the proprietary clamp finishers or jackets available from PYI (http://www.clampjacket.com) or Clamp Aid (http://www.clamp-aid.com). The finisher safely envelopes the sharp end of the clamp and is especially useful in high-traffic areas, the aforementioned galley, and head sink, bilges, etc. Beware of clamp finishers that are made of hard materials as they easily fall off clamps, often clogging bilge pumps. The above-mentioned products are made using an especially supple and sticky silicone-based material that adheres tenaciously to the clamp.
The same caveat holds true for the exposed portion of the shank on T bolt clamps. While less sharp, these still present an injury hazard and are a nuisance as they tend to catch clothing and gear. And, while on the subject of T bolt clamps, if an oversized T bolt clamp is used, there is the risk of it two blocking or running out of adjustment before it imparts the proper amount of tension to the hose installation. Its easy to see if this is the case: if both ends of the clamp are making contact with each other, with no room for adjustment, then the clamp is incorrectly sized and could allow the hose to separate from its adapter.
DOES IT REALLY MATTER HOW THE HOSE IS ATTACHED?
Recently, while carrying out an engine room inspection aboard a vessel undergoing sea trials, I experienced firsthand just how flawed the pipe nipple as a PTH can be. While the vessel was operating at full power I made my way through the engine room, and using an infrared pyrometer, checked the temperature of various components. After I had completed my rounds I stepped out of the space and closed the hatch behind me. As I did so, through my hearing protection I heard a loud whoosh. My hand was still on the handle and I instinctively re-opened the hatch; a cloud of steam billowed through the opening. After telling the operator to shut down the engine I re-entered the space and determined that the source of the steam was a failed coolant hose. The vessel was equipped with a keel cooler that was plumbed to the engine via and a set of 1-7/8-inch inside diameter hoses, which were terminated at the engine using, you guessed it, a set of pipe nipples. In spite of the fact that the hose was double clamped it slipped off of the threaded nipple, spewing the entire contents of the cooling system, roughly 10 gallons of 200°F coolant, around the engine room. Just moments before this had occurred I was standing in front of the engine, where these hoses were located, taking temperature readings of the expansion tank. Had the hose released while I was standing there, its likely that I would have been severely burned.
When it comes to hose clamps and their installation, take no chances. Use only the highest quality, most durable, properly torqued clamps and ensure that they are installed over proper pipe-to-hose adapters. If the pipe-to-hose adapter will support two clamps, by all means double up, and if double clamps are required for ABYC compliance, then ensure twin clamps are used.