Ports in Flexible Containers

Radio frequency (RF) welded flexible containers range in size from small medical infusion bags through beach balls and kiddie pools up to inflatable boats and other large constructions. They are fabricated from thin films for small and disposable items up to heavy-duty, multi-layer materials for more robust applications. And they are applied to numerous purposes; in many of which they are not even seen for what they are.

The one thing they all have in common is that there needs to be one or more connections through the envelope of the container. These ports—that allow the flow of fluids (liquids and gases) into and out of the container—include a variety of devices suited to the specific applications of the designs.

Port placement

There are two basic locations for ports on a flexible container:

  • On a seam where two walls of the container come together.
  • At a location away from a seam through a container wall.

As with most design decisions, there are trade-offs between the two locations including economy of manufacturing and final functionality of the product.

Many products include only one port, but the number that can be applied is limited only by the space available on the product.

heat sealed medical products

On-seam ports

Two on-seam arrangements are available:

  • A tube welded into the seam.
  • A molded or 3D printed boat shaped element welded into the seam.

In general, on-seam connections benefit from:

  • Being less complex with fewer parts.
  • Requiring fewer manufacturing steps since they are installed as part of the container manufacturing process.
  • Multiple ports can be applied at the same time.

Welded tube

A tube welded into the seam of a container is the simplest kind of port. It not only provides a passage into the envelope, but its outer end also provides for attachment of external closures and control devices as well.

Those closures and devices are normally applied to the tube as a subsequent operation to the welding of the envelope.
This port can be configured as shown with the tube extending into the envelope.

Alternatively, for complete gravity drainage of liquids, the envelope adjacent to the port can be shaped into a sump.

Radio Frequency tube welding
Heat sealed tube port

Boat shaped port

This molded or 3D printed item is more elaborate than a simple tube but is applied in similar fashion to a tube.
The illustration shows a barbed stem for connection of a tube or other external device.

That connection could be replaced by a threaded hole or other feature to accept the external device.
This arrangement inherently provides for complete gravity drainage of liquids without needing to specially configure the walls of the envelope.

Through wall port

Two through wall arrangements are available:

  • A welded-on port with a connector protruding from a circular flat flange.
  • A threaded compression fitting mechanically attached through a previously made hole in a container wall.

In general, through wall ports benefit from:

  • The ability to locate the port at any desired location on the envelope. For example, the mouth inflation tube on a life vest must be positioned adjacent to the mouth of the person wearing the vest.
  • The availability of a wide variety of components that include various sizes, shapes, and features from specialty manufacturers.
  • However, through wall ports do have some limitations:
  • They must be applied to the wall material prior to the welded assembly of the container.
  • This always represents at least one additional manufacturing step per port.
  • They cannot be located close to a seam.

Welded on port

The port shown in the illustration is parallel to the container wall. Other configurations can have the connection perpendicular to the wall or any angle in between.

All these ports incorporate the flat flange for welding to the container wall but can include a variety of attachment sizes and shapes.

A more robust welded-on version can include internal or external screw threads to share some of the versatility of the threaded compression type.

RF welded tube port
Air bladder compression fitting valve

Threaded compression fitting

While it is the most complex type of port, the threaded compression fitting is perhaps the most versatile of the four types.
These ports are often seen in recreational and industrial applications since:

  • They allow connection to iron pipe threads and industrial tubing.
  • They can be sized to accept Boston valves that are widely used on inflatable boats.
  • They can be fitted with pressure relief valves.
  • As with all mechanical connections, care is needed to properly assemble this port to avoid leakage.

Since they are not welded to the container wall, these ports can be made from any appropriate material without being limited to RF weldable ones.
Importantly, as long as the fitting is intact, valves or other devices screwed into it can be removed and replaced in case of their failure, for maintenance, or for change of function.

In sum

The port type and method of attachment is a vital element in a flexible container’s ability to serve its intended purpose.