Pick the Proper Hose

Making a correct choice requires an understanding of hose components.

By Patrick Werrlein, Swagelok Company

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These are your next consideration. In most cases a flexible, stainless-steel woven braid reinforces the core tube to improve pressure containment and flexibility in the hose. Ensure your hose has an acceptable pressure rating.

You also must consider flexibility. To do so, you must understand that every hose has a minimum bend radius, which measures how far the hose can bend before kinking (Figure 4). Minimum bend radii are given in industrial hose literature.

However, many people don't realize that flexibility involves more than bend radius. You must consider the force required to bend an unpressurized hose. A hose with a good bend radius isn't much help if it's so stiff that personnel can't bend or have difficulty installing it. Will it slow down or break a machine in a dynamic operation?

Force-to-bend is just as important as bend radius but not as easy to measure — and hose manufacturers don't offer guidelines. So, if feasible, test hose samples with your own hands.

Next, you must decide if your hose should have a cover — and, if so, what kind. A cover is an outer layer that protects underlying layers, personnel and surrounding equipment. Covers come in materials such as silicone and rubber and are integral to the hose.

Silicone covers are most common for general purposes. They help prevent abrasion from fraying the braids in stainless-steel reinforcement layers, which can weaken the hose and create threats of bursting and personal injury. Silicone covers can afford enhanced burn protection for personnel who grab or bump hoses carrying very hot fluid. They also provide insulation, helping to maintain process temperature.

Silicone covers are a particularly good choice for sanitary applications. Their smoothness eases wash down. And covering the stainless-steel reinforcement layer eliminates bacterial buildup in the braid's crevices.

You'll also find covers for specialty applications. For maximum burn protection, consider a fire jacket, a fiberglass cover coated in silicone rubber (Figure 5). Keep in mind, however, that fire jackets connect loosely to the hose and can snag and rip. Another cover type, bend restrictors, help keep hose from being bent beyond its bend radius.

On the downside, covers add cost, restrict flexibility and make the hose larger, a concern for routing and angling. In most applications, the goal in cover selection is to achieve the smallest diameter while not decreasing hose flexibility.

Most leaks occur at the end connections, which usually are made of metal. The performance of a hose assembly largely depends on the hose maker's ability to attach end connections, so choose a reputable manufacturer.

Metal hoses come with a variety of end-connection choices. The connections are welded, which completely and permanently seals the product.

For fluoropolymer hoses, you must select between swaging and crimping. Swaging puts pressure on the hose itself, while crimping squeezes the end connection. Both methods are widely accepted but crimping has a slight advantage in that it's less likely to damage the hose because the pressure is exerted in a carefully controlled manner.

Many chemical applications require use of fluoropolymers on wetted end connections. The hose industry has devised some creative solutions. One is "flare-through" — the fluoropolymer core tube is flared such that it covers the entire inner surface of the metal end connection. This avoids a step or drop between the core tube and fitting, ensuring smooth flow. However, flare-through is costly and fragile and isn't recommended for high temperature applications.

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