Rotary unions, also known as rotary joints or swivel joints, are mechanical devices that provide a rotating connection between two fluid or more carrying channels. They are commonly used in various applications, such as rotary indexing tables, machine tool spindles, packaging machinery, printing presses, and other kinds of equipment or device.

Normally, There are several different types of rotary unions, including:

1. Single Passage Rotary Union: This is the most basic type of rotary union, providing a single flow passage for transferring fluids from a stationary pipe to a rotating pipe or vice versa. It allows for the transfer of a single fluid, such as air, water, hydraulic fluid, or oil.

2. Multi-Passage Rotary Union: Unlike single passage rotary unions, multi-passage unions provide multiple flow passages, allowing for the transfer of multiple fluids simultaneously or individually. They are used in applications where there are request to transfer different media or where separate circuits need to be maintained.

3. High-Speed Rotary Union: These types of rotary unions are designed to handle high rotational speeds while maintaining a reliable and leak-free connection. They are commonly used in applications such as high-speed machining centers, spindle applications, and rotary index tables.

4. High-Pressure Rotary Union: High-pressure rotary unions are specifically designed to handle fluid pressures above the normal range. They are built with robust materials and seals to ensure the integrity of the connection under high-pressure conditions.

5. High-Temperature Rotary Union: These rotary unions are designed to withstand elevated temperatures. They incorporate special materials, seals, and cooling mechanisms to prevent overheating and maintain the efficiency of the fluid transfer.

6. Through-Bore Rotary Union: Through-bore rotary unions allow the passage of fluid, gases, air or electrical signals through the center of the joint. This type of rotary union is often used in applications where it is necessary to pass media or signals through a rotating structure, such as rotary tables or rotary indexers.

7. Hybrid Rotary Union: Hybrid rotary unions combine the functions of fluid transfer and electrical slip rings in a single device. They enable the transfer of both fluid media and electrical power or signals through a rotating joint.

8. Customized Rotary Union: In addition to the standard types mentioned above, rotary unions can be customized to meet specific application requirements. This may involve modifications in size, materials, number of passages, sealing mechanisms, and other factors to ensure optimal performance in a particular application.

These are some of the common types of rotary unions available in the market. The specific type of rotary union chosen for a special application depends on factors such as the type of media being transferred, operating conditions (pressure, temperature, speed), and any additional requirements, such as electrical connections.