Loading arms are used to load liquids into tanks, trucks, railcars, and other vehicles. They are commonly used in fueling and fluid transfer applications. Loading arms are available in a variety of sizes, lengths, and designs. Most are made of aluminum, carbon steel, low-temperature carbon steel, or aluminum. Products that are designed to handle corrosive or high-temperature materials are often jacketed or lined with polytetrafluoroethylene (PTFE), a highly-resistant plastic with very low flammability. Seals are made of proprietary materials such as Buna N, Viton, and Teflon, registered trademarks of DuPont. To provide flexibility, swivel joints are inserted between straight lengths of the loading arm. Torsion springs or counter weights are sometimes used to provide supported vertical movement. Loading arms with supported booms have a greater reach than devices with unsupported booms. Components and accessories for loading arms include dry break couplers, mechanical or pneumatic breakaway couplers, shut-off valves, level sensors, vacuum breakers, and deflectors. There are many different types of loading arms. Examples include top loaders, bottom loaders, pantographs or scissor arms, slide sleeves, wash arms, vapor recovery loaders, and counterweighted loaders. Top loaders are designed for the loading and unloading or rail cars through open domes which operators can spot. Some products can also be used in tight-fill or closed-system applications. Bottom loaders are designed to fit the underside or undercarriage of trucks, tanks, and railcars. They have a long, articulated arm that can be stored in a near-vertical position. For applications that require multiple connections, riser heights can be staggered to achieve crossover. Slide sleeve loaders feature an inner tube, an outer sleeve, and heavy-duty seals. Vapor recovery systems are designed to recover the fumes from gasoline during the fueling of vehicles. Spring-balanced and counter-weighted loading arms are also commonly available. As a rule, counterweighted arms require more clearance for operation. Loading arms differ in terms of specifications, applications, and features. Specifications include diameter, flow rate, maximum pressure, and temperature range. Torsion springs can swivel to the right or to the left. Inboard flanges and outboard flanges are specified as face-up or face-down. In terms of applications, loading arms are used widely in the chemical, petrochemical, pharmaceutical, oil and gas, and food and beverage industries. Some products are designed for bulk liquids heated to +232° C , or liquefied gases that are cooled to -196° C. Others are rated for hazardous or corrosive fluids.