Flex Connectors for Bulk Material Handling

What a flex connector does

Two jobs, at the same time. It seals the joint so material and dust stay inside the line, and it decouples the two pieces of equipment so movement in one does not travel into the other. A bucket elevator vibrates. A fan vibrates harder. A truck settling under a loading spout moves the spout an inch. Rigid pipe transmits all of that. A rubber sleeve absorbs it.

That second job is why wall thickness is not simply a durability question. A sleeve that is too stiff for its diameter stops flexing and starts transmitting, which puts the load back into the equipment flanges you were trying to protect. Match the wall to the material running through it, then let the length give you the slack.

The terminology trap, and it is a real one

The same rubber part has different names in different plants, and one of them causes actual ordering mistakes.

In grain handling, a boot is the bottom section of a bucket elevator. It is the steel housing where the belt turns around the tail pulley, and it has nothing to do with rubber. In concrete and aggregate, a boot is a rubber discharge sleeve. Two industries, one word, two completely different parts. When a grain operator calls a supplier and asks for a boot, a quote comes back for elevator housing components. When a batch plant operator asks the same question, a quote comes back for a rubber sleeve.

The names you will hear for the rubber part: flex connector, flexible connector, spouting sleeve, transition sleeve, bin discharge connector, dust sock, silo band, elephant trunk, and boot. They mostly describe the same thing in a different accent.

You can skip all of it. Give us the inside diameter, the wall thickness and the length, and the vocabulary stops mattering.

Sizing a flex connector

Inside diameter is the outside diameter of the pipe or spout it slips over. Round spouting and pipe are named by nominal size and measured by something bigger, so 8 inch pipe is 8.625 inches across, 10 inch is 10.75, and 12 inch is 12.75. Order by the measurement, not by the name.

Wall follows the material. Grain, cement, flour, fly ash and dust run fine at 1/4 inch. Aggregate and anything with sharp edges wants 3/8 inch. Heavy impact spots go to 1/2 inch.

Length is the gap plus 3 to 4 inches of overlap on each end for the clamp bands. Add a little extra so the connector hangs with slack. A connector pulled taut is a rigid pipe with a rubber section in it.

See the 8 5/8 inch gum rubber boot for the most common connector size, browse all sizes, or find your equipment under industries.