未分类 · 2021年12月21日

What exactly is a Valve Connection?

The components of a valve that connect to the plumbing and allow the valve to connect to the piping system are known as valve connections. There are six major types of connections used to install valves and other process components in piping systems, each with advantages and disadvantages:

Threaded \sWelded \sFlanged \sCompression
Union \sManifold-mount
It is critical to consider the following factors when selecting a type of valve connection:

Compliance with industry and/or plant standards
Cost
Installation ease Ease of removal for repair or replacement
Simplifying inventory
Preventing leaks
The valve’s durability
System pressure/pressure rating
Size and weight

The type of connection that will be most effective will be determined by the specifications of your system.

Valves with Threaded Balls
Threaded valve connections are among the most common types of valve connections. To integrate with the piping system, this valve style incorporates a screw-type design. Threaded valve connections can be made in three different ways:

Female x Feminine
Male to Male x Male
Female x Male
Threaded valve connections provide a secure and streamlined connection between the valve and the pipe. Female threaded connections on valves are most commonly used to fit over the end of a male threaded pipe. To be compatible, the threads on both the valve and the pipes must follow the same standard thread design.

Ball valves with threaded connections are simple to install, maintain, and replace, as well as inexpensive and ideal for smaller applications. Threaded connections are typically preferred in applications involving ball valves with diameters less than 4 inches. This is because larger diameter connections are more difficult to seal and thus more prone to leaks through the threads.

Pipe tape or sealant between the male and female threads is recommended even with smaller threaded ball valve connections as a precaution. Both provide additional sealing, and the sealant also serves as lubricant, preventing metal-to-metal contact and galling.

Connections for Threaded Ball Valves (Straight vs. Tapered Connections)
As previously stated, thread design is governed by industry standards. Threaded connections can be straight or tapered, with three sets of standards determining the exact specifications: National Pipe Thread, British Standard Pipe, and Metric (more on these below).

Straight threaded connections have the same diameter throughout their length and require a washer or soft O-ring seal to keep leaks at bay. Tapered threads, as the name implies, taper in diameter toward the connection’s end. Although tapered connections do not require an O-ring seal, they do require pipe tape or sealant to achieve a leak-tight seal.
National Pipe Thread (NPT) The National Pipe Thread (NPT) is the piping thread design standard in most of North America (excluding Mexico). NPT threads are unified and pitched at a 60 degree angle with flat peaks and valleys, and they can be straight (NPS) or tapered. When male and female tapered threads are joined, they pull tightly against one another, forming a leak-tight seal.

ASME B1.20.1 defines NPT specifications. The major diameter of the connection in inches is used to classify sizes, which is followed by "NPT" (4 NPT).

Threads for British Standard Pipes (BSP)
Except for the United States and Canada, British Standard Pipe (BSP) threads are widely accepted around the world. BSP threads are unified and pitched at a 55-degree angle, with rounded peaks and valleys; they can be tapered or straight, like NPT threads.

Sealant is required for tapered BSP (BSPT) threaded connections to form a leak-tight seal between the male and female components. Because a bonded seal is built into the design, straight or parallel BSP (BSPP) threaded connections do not require thread sealant.

BS EN 10226-1:2004, BS EN 10226-2:2005, and BS EN 10226-3:2005 define BSP threads. For tapered connections, the letters R (rohr, or "pipe" in German) are used, and for straight connections, the letters G (gas) are used, followed by the major diameter in inches (R 2 12).

Thread Metric Standard (M)
The ISO metric thread standard, abbreviated as M, is a global screw thread standard. M threads are parallel, 60-degree pitched, and have flat peaks and valleys. ISO 68-1, one of the first standards established by the ISO in 1947, defines the design.

The most significant distinction between M, BSP, and NPT threads is that M threads are measured in millimeters. Sizes are denoted by the letter M, followed by the major diameter and pitch, separated by a hyphen (M8-1.25). The pitch is the millimeter distance between the crests of two threads.

Connections for Welded Valve
To eliminate the possibility of leaks, valve connections can be welded into a piping system. Welded valve connections are commonly used in high-temperature and high-pressure systems, such as chemical processing, where errors caused by leaks are eliminated. Because the valve must be desoldered in order to be removed from the plumbing, this is generally considered a permanent installation.

Connections for Flanged Valve
Flanges are solid metal plates with bolt holes that are used to surround the edge of a valve connection. When installing a flanged valve in a piping system, the plate can be bolted to another flange on the pipe, resulting in a secure connection. Flanged connections are common in industrial applications and are commonly seen in valves larger than 4 inches in diameter. For routine cleaning, flanges are simple to install and remove. Flanged connections, like threaded connections, must adhere to strict standards that define the plate design, hole size and position, and thread type in the holes (ASME B16.5 – 2020 and ISO 7005-1:2011).
Connections for Compression Valves
Compression connections are classified into three types:

Traditional Compression: A threaded nut and a soft metal cuff known as a ferrule are slid over the end of a pipe, then tightened until the ferrule is forced into the valve socket. Between the valve and the compression nut, the ferrule is compressed, forming a leak-tight seal. Traditional compression connections are commonly used in home plumbing.
Push-to-Connect: An O-ring that is slightly smaller than the outer diameter of the connecting pipe is stretched around the pipe and compressed between it and the valve body inside the valve port. A grab-ring with teeth digs into the pipe and keeps it from slipping out, but the pipe can be easily removed by pressing the release ring and retracting the teeth. Push-to-connect solutions are common in home plumbing systems.
Barbed Hose Connections: These connections are used to connect a soft hose to a valve and are ideal for low-pressure systems. The valve has a long end connection with exterior barbs that bite into the inside of the hose as it is stretched over the connection. The barbs do a good job of holding the hose in place, but a hose clamp is recommended to strengthen the connection.