Coupling Bells, Flares, And Sleeves

A metal tubing sleeve next to a tubing flare with slits cut in the end

Besides solvent welding, there are several other methods to couple your Flares and Bells to our tubing. Many of our customers want to easily access sleeves and couplings for cleaning of the pneumatic line.

Axial Slit and Hose Clamp:

We simply provide four .125″ axial slits in the belled section 1.25″ in length. One (or two) small hose clamps are more than adequate on low-pressure pneumatic lines.

The same applies to belled bends (See 4″ CAB bend, 90° 24″ CLR).

Below, we have the most common union method of coupling a sleeve to tubing. The sleeve has 4 axial slits on each end compressed by a hose clamp.

Because we want to ensure that our tubing provides uninterrupted flow, we do not provide PVC-like couplings and bells. The center ridge in such connectors can influence and disrupt the items traveling through the coupling. So, rather than couplings, a bell with axial slits allows easy slip coupling of the tubing into the bell. Those who convey closures, caps, and small items often prefer this method.

It is especially helpful on belling tubing in excess of 8″ OD. (See 7.5″ ID to 8.375″ ID x .187w Butyrate Bell). In straight-length bells, we specify our resin (butyrate, PETG, PVC, Polycarbonate, etc) with the small ID, the transition, and the large ID.

Tell us your need and we’ll make the print.

Conical Set Screws:

This method simply involves drilling, tapping (butyrate, a cellulosic, taps as easily as if you were tapping into wood), and lightly torquing the coupling into the tube.

Expanded Bell vs Sleeve Bell

Expanded bells have no “bump” and work best in certain conveyance applications. Below is a picture of how to couple an expanded bell to a tubing line. The bell is cut to length, and then solvent welded to a sleeve.

The sleeve, in turn, is solvent welded to the conveyance line. The advantage of solvent welding is that the bond is permanent and will not separate. The disadvantage is that the bond is permanent and will not separate; it requires a saw to remove it.

Solvent Welding Sleeve


Heat coupling.

A customer recently had a need to heat a couple of Provista tubes to a Butyrate Sleeve. The picture below shows that the butyrate sleeve was tight on the Provista tube and would, at best only slip over 1/2″ of it. Since the customer was going to couple the tube with a work crew in the field, they needed a simple way to expand the sleeve.

That simple way is merely a heat gun. It’s simple to do, but the trick is not to overheat the butyrate. The butyrate will expand before softening. We are only looking to expand the butyrate tube about .005 to .010″

At this point, the butyrate sleeve will easily slide over the Provista tube. But you only have about 30 seconds of working time before the butyrate sleeve will start to cool and clamp. When it clamps it is permanent.

Once the tube has cooled you have a permanent sleeve. Since butyrate and Provista expand at different rates, it is possible to separate the two by heating the butyrate sleeve quickly, but make sure that you do not heat the underlying Provista in the process. If so, both materials will expand. It’s best to just consider this operation as permanent.

Flares and Bells (Swages), the difference:

While “bells” are designed to couple tubing, “flares” are designed to allow an object easy entrance into the tubing line. We often fabricate bells to couple different tubing sizes. For example, pictured below we have a transition from a 3″ ID tube to a 4″ ID tube. 3” ID tube to a 4” ID tube. The trick was to do it without tooling. The cup manufacturer wanted only three flares to put at cup entrance points of its pneumatic transport system.

Busada makes all kinds of flared tubing and belled tubing . . . hundreds of kinds . . . and we cater to our customer’s unusual needs. We flare and bell butyrate, polycarbonate, PETG, PVC, and other thermoplastics. We also flare and bell our bends.

Pictured below: A Sleeved Bell Reducer: We do not recommend connecting tubing and bends with traditional couplings (as in PVC lines). Pneumatic conveyance systems need smooth connections, and the traditional PVC-type coupling joint can damage conveyance materials. As Busada 200 Tubing maintains a .005 tolerance in wall thicknesses, we prefer to make our own coupling sleeves. Pictured above is a solvent-welded sleeve on the flare side with four axial cuts on the sleeve side. The cuts allow for clamping of the sleeve on a straight tube or bend with hose clamps.

Finally, PVC-reducing bushings remain an option. Besides losing transparency, the PVC funnel angle of 30° can bump and ding the conveyance material. Nevertheless, we can flare out tubing to pipe dimensions and bond to PVC.

PVC couplings and bells are fine for valve-stem protectors. Check our other blogs on bonding dissimilar plastics with heat and adhesion. Note here that on top of adhesives we recommend a set screw (sheet metal screw) that will bite into the butyrate wall. We can also thread our butyrate pipe on sizes 1 to 4″ pipe sizes.

Fabrication of Flanges, Els, and Bells, Tees and other fittings in Butyrate

Here is an illustration showing our method of fabricating 90° ells from a straight section of CAB Tenite clear extruded butyrate pipe.

This example is from 4″ Sch 40 pipe. The ends of the two pieces to be joined are cut on a 22½° angle. A short filler cut with the 22½° angle on each end is fitted between them. The pipe can easily be assembled in the field, even cut by hand in a miter box. The ends of the cut pipe to be joined are soaked in butyl acetate until very tacky, then pressed firmly together. A bead of acetone cement is applied to the joint and allowed to dry. Other fittings can be made in a similar manner using the proper angles cut in the pipe.

Fabricated flanges and bell couplings are also shown. We have several ways of making them. The bell coupling is necessary for installing a pipe line with a bell-and-spigot type of connection.

Flanges can be fabricated directly from the tubing by heating in a mineral oil bath, external quartz heaters, or by solvent welding butyrate sheeting. The key is for slow heating and setting temperatures to approx 300F.

Here we see the application of a tight-radius ell.

Coupling Dissimilar Plastics by Swaging or Compression Bells

Sometimes our customers need to couple dissimilar plastics tubing. Most often they couple provista (PETG) tubing with butyrate (CAB) sleeves. We recommend this technique. It is simply using the molding shrinkage of a heated tube to form a compression coupling

After inserting the inner tube into the outer tube slide and clamp the hose clamp. You can keep the clamp on, or after cooling remove it (it will leave its impression).

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