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Flexible metallic connectors play critical safety role

November 4, 2021 By    

The regulator connected to the source container is referred to as the first-stage regulator and has the critical safety function of reducing the container gas pressure down to a lower operating pressure. This regulator is commonly connected to the service valve on the container through a connector referred to as a “pigtail” or “hogtail,” which are both flexible metallic connectors.

A pigtail is typically constructed with 0.25-in. copper tubing between the brass fittings, which makes it very flexible. A hogtail is typically constructed with 0.375-in. tubing, which makes it less flexible. The larger tubing diameter in the hogtail allows for greater vapor flow than a pigtail.

Both types of connectors come in a variety of sizes and styles. The connection to the service valve should always be POL, but the connection to the inlet of the regulator can vary depending on the regulator selected. These flexible metallic connectors play a very important safety role at the start of the propane vapor distribution system. The Propane Education & Research Council has educational materials for designing and installing vapor distribution systems – found at propane.com and in the Learning Center.

Safety functions

The National Fire Protection Association states that the connection between  tank and regulator must be attached directly or attached with a flexible connector to the shutoff service valve outlet. The connectors cannot exceed 5 ft. in length when used on stationary containers of 2,000 gallons or less.

Flexible metallic connectors (pigtails or hogtails) provide a critical safety function as they allow for movement in the gas piping at the container. This flexibility reduces stress on rigid piping and fittings, absorbs vibrations and reduces shocks to the piping system at the container.

Flexible metallic connectors (pigtails or hogtails) vary in length, and many are straight (not bent) from the manufacturer. Since connectors are flexible, service technicians can bend or loop them for any number of applications, ensuring the regulator is properly positioned under the container dome. There are also pre-bent connectors for specific applications like underground containers where tight space can be an issue.

Kinks in the flexible connector, which can restrict the flow of vapor and create a place for debris to collect, should always be avoided, and excessive bending or twisting can stress the tubing, which can lead to a crack and cause a leak.

Corrosion concerns

It is important to understand how flexible connectors can react with propane vapor. The interior surface of a copper flexible connector can become brittle as the hydrocarbon (propane) gas flows through it. Copper sulfate can form along the copper surface, resulting in flakes that can come loose and travel to the inlet of the regulator. Therefore, you don’t want to reuse or reposition flexible connectors that have been installed. It is important for propane professionals to be mindful of how debris can affect the safe operation of a propane system.

Flexible connectors (pigtails or hogtails) can catch or trap debris coming from the container. Debris can obviously cause a blockage that can obstruct the flow of gas vapor to the regulator. Debris like a corrosion (copper sulfate) flake or excess thread sealant can get stuck on the seat disc, resulting in the regulator orifice not sealing completely, which stops the regulator from reaching lock-up. Debris of any sort that enters the inlet of a regulator can cause the regulator to “creep,” which can lead to increased outlet pressure, causing the internal relief valve to activate.

Although it may be a small item in the total propane vapor distribution system, remember that if you are replacing a regulator or switching a container, always replace the flexible metallic connector (pigtail or hogtail). By properly selecting and correctly installing these connectors, you are ensuring the safety of the operating system that helps ensure you provide clean, efficient propane energy to your customers.


Randy Warner is the product safety manager for Cavagna North America. He can be reached at randywarner@us.cavagnagroup.com.

NOTE: The opinions and viewpoints expressed herein are solely the author’s and should in no way be interpreted as those of LP Gas magazine or any of its staff members.

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