Choosing a PVC pipe belling system
There are several systems used by manufacturers of PVC pipe to form the raceway that accepts the gasket in the pipe bell. Some methods form the raceway using a collapsible type belling head, others form the raceway by molding the bell, and some form the raceway using the Rieber method where the gasket becomes an integral part of the belling process. Choosing the proper system can offer significant advantages to the pipe producer as well as the end user.
PVC Pipe Joint with RIEBER GASKET
Collapsible belling heads expand to define the gasket raceway, and then properly heated PVC pipe is pushed over the head and expanded segments. Vacuum and/or external pressure is applied to help conform the heated pipe to the belling head. In some cases mechanical clamps or sleeve are used to help form the bell. After the pipe is cooled using water, the belling segments collapse so the pipe can be removed. The gaskets are installed after the belling process.
The collapsible type belling tool consists of many moving parts that are exposed to a hostile
environment. The quality of the gasket raceway can be compromised if the tool wears or does not fully expand. When this occurs, ridges are formed on the inside surface of the gasket raceway providing avenues for potential leakage. With the tool exposed to process water during bell cooling, corrosion is a concern as parts wear faster as they corrode. Maintenance on this type of belling tool is extensive and parts are not inexpensive.
Collapsible type belling tools are expensive when purchased with the price increasing dramatically, as the sizes get bigger.
Molding can form the gasket raceway with pressure applied to the inside of the heated PVC pipe forcing it to conform to a mold on the outside of the pipe. The raceway and bell are then cooled before and after the mold is retracted. The outside of the pipe bell comes in contact with the mold, not the inside. The quality of the raceway is dependent on the quality of the pipe being belled, as variation in wall thickness and inconsistency in the pipe will be transferred to the raceway. The gaskets are installed after the belling process.
PVC Pipe Joint with RIEBER GASKET
Note Metal Band bonded to Rubber Surface
With the Rieber system, the gasket forms the gasket raceway. Heated pipe is pushed over a belling mandrel that has a Rieber gasket installed on it. After the pipe is pushed over the mandrel and Rieber gasket, vacuum and/or pressure is applied to conform the pipe to the gasket and mandrel. Using the Rieber gasket to form the raceway ensures the gasket always conforms to the raceway. Once cooled, the pipe bell is pushed off the mandrel with the gasket secure in the raceway. A metal band or ring embedded in the Rieber gasket secures the gasket in the bell.
Collapsing belling mandrels are between 3 and 4 times more expensive to machine and assemble than Rieber mandrels. Choosing Rieber gaskets results in a significant reduction in needed capital expenditure. The Rieber belling mandrels are relatively inexpensive, and have no moving parts. Corrosion is not a concern as all surfaces are treated to resist corrosion. Maintenance is limited to periodically cleaning of the vacuum ports and mandrel surfaces. Loading the Rieber gaskets onto the belling mandrel is normally accomplished by using an automated gasket loader.
Belling equipment needed for the Rieber system is manufactured and available around the world, with major suppliers on every continent with the exception of Antarctica. Over the years equipment manufacturers have refined designs, and with the help of technology can provide automated trouble-free belling systems that produce high quality consistent bells.
The Rieber gasket system offers advantages to the installer as well. With a metal band, or ring, securing the gasket in the bell, dislodging the gasket during assembly of pipe joints is extremely difficult. The Rieber gaskets are installed and “locked” into the bell of the pipe during the pipe manufacturing process. No gaskets to lose or install in the field.
The Rieber gasket comes in many configurations designed specifically for end-use. It can use a compressive seal well suited for pressure pipe. It can use a lip seal for low pressure irrigation applications. It can use a combination of compression and lip seals to balance sealing and assembly force.
Rieber gaskets can be supplied in a variety of specialty elastomers to ensure long life when exposed to harsh environments. Gaskets that are bonded to a plastic retainer may have limited elastomer offering, as some plastics and elastomers, for example nitrile rubber and polypropylene plastic, are not compatible. Gaskets that use splicing to manufacture are also limited, as not all elastomers can be bonded together. The metal band, or wire, in the Rieber gasket allows just about any elastomer to be used in manufacturing.
In conclusion a pipe company has several equipment choices when making gasketed belled PVC pipe. Based on the many factors as mentioned, the Rieber belling system and the Rieber style gasket offer a significant number of advantages.