Rubber Bellows Seal Fitting: Which Lube to Use

A rubber (elastomer) bellows seal has no grub screws and no clamp. The rubber bellows grips the pump shaft, and that grip is what turns the seal face. Fit it with silicone or the wrong grease and the rubber may never grip properly, so the shaft can spin inside the bellows and the seal fails early.

What drives a rubber bellows seal?

The elastomer bellows grips the shaft tightly. That friction grip drives the seal face round with the shaft. There are no set screws to lock it. If the rubber cannot grip, the face slips, the seal runs hot, wears fast, and leaks.

Which lubricant should you use?

Use the lubricant the seal maker states in the fitting instructions. Many call for soapy water or a water-based rubber lubricant. It lets the seal slide into place, then dries off so the rubber can grip the shaft.

Why not silicone, oil or grease?

Silicone lubricants can stop a bellows seal gripping the shaft after fitting. Several seal makers say not to use oil or grease on the shaft for the same reason. Only use them if the seal maker allows it.

Can it still fail with the right lube?

Yes. Sharp keyways, threads and shaft edges can cut the rubber as the seal slides on. Cover them with thin tape or use a fitting sleeve, and check the fitting length before you start.

What to ask your supplier

Ask for the seal's fitting instructions, including the approved lubricant and the fitting length. A rubber bellows seal is a simple, reliable component seal for water pumps and other clean-liquid duties, as long as it goes on the way the maker intended.

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