Ball valves are popular in domestic and industrial applications because of their wide range of use, low cost, and ease of maintenance. Different applications and installation environments of ball valves require different types of end connections to properly connect to process pipes or components. Though the connection types essentially do the same thing: to attach the ball valve to the pipe or component at both ends, some connection types are more advantageous for different applications.
The most common types of ball valve connections: flanged connection, welded connection, true union, tri-clamp, and threaded as seen in Figure 1.
Figure 1: Ball valve connection types: flanged connection (A), welded connection (B), true union (C), tri-clamp (D), and threaded connection (E).
Threaded connection ends are an easy way to connect small valves to pipes. They are typically used in applications that have small ball valves with a diameter less than 4″ because larger diameters will be difficult to seal and are prone to leakages through the threads. They are cheap, easy to install, and easy to maintain and replace. Typically, the valve has female threaded ends that connect to a male threaded component. In some cases, the valve has male threaded ends or one male threaded end and the other a female threaded end. The threads are made by adhering strictly to thread standards, which specify the parameters of the thread. An example of a ball valve with threads can be seen in Figure 2.
Threaded connections can either be straight or tapered. Straight connections often require an O-ring that compresses to ensure a tight seal between the valve and the pipe. The tapered thread does not require an O-ring to achieve a tight seal. Both types of thread can use pipe tape or a sealant between the male and female thread, which serves as a lubricant, provides sealing, and prevents metal-to-metal contacts that cause wear.
There are three main types of international thread standards that define the parameters of the thread.
Figure 2: Ball valve with threaded connection.
British Standard Pipe (BSP)
BSP is a widely accepted standard for sealing pipes and fittings in most parts of the world, with the notable exception of the United States of America. The BSP consists of both female and male threaded ends for the valve and pipe. They have a flank angle of 55 degrees with rounded roots and crests (valleys and peaks).
The BSP standard has two types of thread: the parallel (straight) threads BSPP and the taper threads BSPT. The BSPP is defined by the standards ISO 228-1:2000 and ISO 228-2:1987, while the BSPT is defined by the standards ISO 7, EN 10226-1, and BS 21.
American National Standard Pipe Thread
This is also known as the National Pipe Thread (NPT). It also has a standard for both tapered and straight thread types. The flank angle is 60 degrees with flat roots and crests. There are many types of NPT, but the two main types are the American National Standard Taper Pipe Thread (also known as NPT) and the American National Standard Straight Pipe Thread (NPS).
Metric Thread Standard (M)
Metric threads are a general-purpose screw thread standard. It is a parallel type thread known by the ‘M’ designation followed by a number indicating the threads major diameter. The major diameter and the pitch size is used to characterize the thread standard. It is a V-shaped thread with a flank angle of 60 degrees. The metric thread is defined by the standard ISO 68-1.