Hoses and clamps -commonplace but critical

For want of a clamp, the coolant is lost; for want of coolant the engine is lost; for want of an engine, the truck is lost; for want of a truck, the business is lost." Please forgive the reworking of the old adage that begins, "For want of a nail, the shoe is lost . . ." But it makes the point that inattention to a small detail - like selecting a hose clamp - can bring on dire results.

While engine manufacturers search for ways to achieve the best possible balance of economy, performance and lower emissions, designers of vehicle cooling systems face the problem of developing cooling systems and components that will support those engines - whatever they may be - come Oct. 1, 2002.

In an effort to tell fleets what tomorrow's cooling system will look like and what it will be able to do, The Maintenance Council (TMC) of the American Trucking Assns. offered a technical session, "What's Happening to Vehicle Cooling Systems," at its summer meeting in Tucson, Ariz. Subjects ranged from clamps and hoses, which we look at here, to coolants and fleet experiences with the newer coolants, which we'll report on later.

Recent developments in hose clamps and hoses were reviewed by Rod Ward, director of sales engineering for Flexfab Silicone Hose Div., who pointed out that many of the new products were responses to the 1,000,000-mile challenge issued in TMC's "Tomorrow's Truck" paper.

Among some of the newer clamps described by Ward were constant-torque clamps, one with a helical spring, and another, for heavier-duty applications, with belleville washers under the drive head. Both have a metal band on the inside to keep the clamp round and prevent formation of "steps" that could transfer down to the sealing surface and result in cold leaks when the system cools down.

"Constant-tension clamps," Ward noted, "basically have the torque, or squeeze, built in." Some are pre-latched in the open position, so all a technician has to do is flip the latch and they snap shut. Because this clamp has little tolerance for hose-wall variation, there is now an SAE-spec, precise-tolerance wall hose for use with this clamp.

Other constant-tension clamps have little beads or "wave springs" on the inner band of the clamp. The idea here is that, as the clamp is tightened down, the waves, in effect, create a rubber O-ring that provides a better seal.

Then there is a polymeric clamp that slips over the outside of the hose. When heated with a heat gun, the clamp shrinks into position. A room-temperature version is kept in a freezer until needed, at which time room temperature will cause it to shrink.

Ward also described a preassembled clamping system used in a European auto application. It consists of a metal or plastic insert that slips into the end of the hose. On the inside of the insert are an O-ring, which seals on the stem, and spring latches that snap into clamping position when the insert slides over the stem.

Turning to hoses, Ward told TMC attendees that silicone hoses and EPDM rubber hoses are now available with single-ply and multiple-ply reinforcement, standard or thinner wall, and burst pressure ratings of about 150 or 350 psi. "With that higher rating, you'd turn the radiator inside out before you'd blow the hose," he said.

TMC is working on a new Recommended Practice, RP 303B, "Coolant Hose Service Life Rating Factors," that will rate hoses by continuous-use exterior temperature, minimum low-temperature flexibility, splash resistance to fluids (oil, salt spray, diesel, power steering, brake, washer), and abrasion resistance. (These ratings would be on top of SAE specs the hoses must meet.)