There are few applications where perforated tubes can function as needed without some kind of cap or fitting at one or both ends. Fittings provide mounting and connection options while end caps ensure fluid passes through the perforations rather than out the end of the tube. Here’s an explanation of your options for perforated tube end caps and fittings.
There are two ways of joining one perforated tube to another tube or mounting point: the joint is either flanged or threaded. (Welding is excluded on the grounds that it’s not a joint that can be easily disassembled.)
Flanges are annular rings that fit around the outside diameter. They have bolt holes that need aligning between the two flanges being joined so bolts can be slipped through. Usual practice is to put a gasket between the two flanges then torque the bolts enough to compress the gasket material without crushing it completely.
Threaded connections require male and female threaded end connectors on both sides. These are screwed together to complete the assembly, often with PTFE or plumber’s tape sealing the threads. The tube end typically looks like an end cap with a threaded section extending out of the center.
Considerations for Flanges and Threaded End Connectors
One disadvantage of threaded end connectors is that one of the perforated tubes must rotate for assembly. The practicality of this varies by application. In filters it’s a logical way of attaching and detaching the assembly to and from the oil supply line. Elsewhere, perforated tubes with flanges are generally easier to swap out and replace in service.
High precision manufacturing is essential for both types of connection. The flange or threaded end connector must be a tight fit on the perforated tube, bolt holes must line up, and threads must mate correctly. Achieving this level of fit demands excellent manufacturing process control and strong measurement capabilities.
Requirements for End Caps
An end cap is disc closing off the end of a perforated tube. This is usually used to force fluid to flow through the openings in the tube. Secondary reasons for specifying an end cap are to prevent damage and add strength. As such, the end cap has no requirement for connecting to a flange or thread. However, it must still be manufactured with sufficient precision to fit correctly over or into the tube.
In some applications it may be desirable to perforate the end cap. This would allow a controlled degree of fluid flow. and some filtration applications may benefit from perforated end caps. In such circumstances the same requirements for open area and hole size and shape apply as for perforated tubes themselves.
An end cap, flange or threaded end connector is usually fabricated from the same material as the perforated tube to which it will be fitted. If the tube material is stainless steel for example, (a popular choice when corrosion resistance is needed,) the cap, flange or connector will most likely be the same grade. Using dissimilar materials poses a risk of galvanic corrosion and temperature-induced distortion.
As with tubes themselves, end caps and connectors can be produced in:
- Mild Steel
- Stainless Steel
In addition, the same finishing options – plating, electropolishing (stainless) and powder coating – are available.
Consider the End Fittings
The primary role of perforated tubes is to filter. Usually they let fluid pass in a controlled manner while holding the filter media (fiberglass, paper, wire wool,) in place and blocking particles above a certain size. Sometimes they will screen or filter light or sound. Whatever the application though, the tube needs holding in place, and that’s where end fittings come in.
When specifying or inquiring about perforated tubes, always consider what will go at the ends. The tube needs some means of connection, either flanges or thread, to another tube or to some mounting point or pipe. It may also need a fitting to stop fluid taking the path of least resistance and flowing out of the end – an end cap in other words. And don’t overlook that end caps add strength and rigidity to the tube.
End fittings for perforated tubes offer a lot of choices. Gain a more complete understanding of the options by discussing your application with a perforated tubing specialist.