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There are quite a few different types of connections used to install valves and other process components in piping of process systems. While they all perform the same function of connecting the valve into the piping system and allowing it to perform its function, each connection type has its own pros and cons. The selection of the best valve connection type for your application is based on many factors:
Factors for Selecting a Connection Type
Threaded connections are very common. They provide a compact and streamlined connection between the valve and pipe.
The valve typically has female threaded end connections, into which the male threaded pipe fits. There are valves with male threaded connections as well, and even valves with one female end and one male end. Threaded connections must adhere to a standard in order to be useful in industry. There are a few different standards that exist. The valve and pipe must both be created using the same standard in order for them to make a proper connection.
There are standards for straight threads and some for tapered. Tapered threads provide a fluid tight seal without the use of a soft seal like an o-ring or flat washer. Straight threads do require a soft seal that gets compressed between the valve and pipe, hose, or fitting that they are being connected to.
Male vs. Female
Straight vs. Tapered
Anatomy of Threads
This is a U.S. standard for tapered threads used on threaded pipes and fittings. In contrast to straight threads like those that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. Pipe tape or pipe compound should be used on the threads to ensure a fluid-tight seal.
NPT is defined by ANSI/ASME standard B1.20.1.
There are 25 sizes defined from 1/16" to 24", (see chart with sizes and dimensions) however typically valves over 4" will use flanged connections rather than threaded.
NPT threads are specified using the size in inches followed by "NPT".
example: 2" NPT
This standard is similar to NPT, where the threaded portions of the connection are tapered. The only difference is the angle of the thread flanks. The angle from root to crest on BSPT threads is 55° as opposed to 60° for NPT. It is possible for a male NPT to fit into a female BSPT, but due to the difference of the thread angle a fluid tight seal will not be made.
BSPT threads are defined by ISO 7 and/or EN 10226-1, BS 21.
BSPT threads are specified using the letter "R" followed by the size in inches. R stands for "rohr" which is german for pipe.
example: R 2 1/2"
This type of thread does NOT form a fluid tight seal like the tapered threads do. The use of a soft seal is required to do so. These threads will pull the 2 mating parts together, and compress the soft seal between flat surfaces on each component.
BSPP threads are defined by ISO 228-1:2000 (Dimensions, tolerances, and designation) and ISO 228-2:1987.
BSPP threads are specified using the letter "G" followed by the size in inches. G stands for "gas".
example: G 1/2"
The valve simply has a socket with an inner diameter that is ever so slightly larger than the pipe's outer diameter. The pipe is inserted into the socket, and is welded around the rim as shown here. Socket weld connections are usually reserved for smaller sizes, typically 2" and below. They are permanent connections that are reliably leak-free. This example includes "heat sink" fins which help dissipate heat to protect the seals during welding. Valves with this feature are often referred to as "weld-in-place."
Note: These welds should be performed by a trained .professional.Care must be taken to avoid damaging the seats and seals with excessive heat.
The valve end and the pipe end are of equal diameters. The outer edge of each is chamfered to create a "valley" to be filled with welding material. The two pieces are welded around the rims as shown in the illustration. Butt weld connections are usually reserved for smaller sizes, typically 2" and below. The example shown here also includes the heat sink fins.
Note: These welds should be performed by a trained profesional. Care must be taken to avoid damaging the seats and seals with excessive heat.
This is the most common connection type in residential plumbing systems. This connection type is very similar to socket weld. The pipe fits snuggly into a smooth bore on the valve, then the connection is soldered by heating the valve bore and touching the seam with solder which melts and gets drawn in and around the entire circumference of the pipe/valve seam.
While there are situations where soldering a connection may be dangerous, difficult, or even impossible, they do provide a very rugged and reliable connection that can withstand shock such as water-hammer, temperature fluxtuations, and flexing.
Glue socket connections are also referred to as FIP, slip-fit, friction fit, pipe end, or spigot connections. They are very simple. The inner diameter of a glue socket connection is ever so slightly larger than the outer diameter of the pipe, which simply inserts into the socket. PVC cement is used (prior to inserting) to attach PVC or CPVC valves to PVC or CPVC pipes. It is recommended to twist the pipe 1/4 turn as it is inserted. The cement actually melts the pieces together making them permanent. These connections cannot be un-done.
Most flanged end connections adhere to an industry standard. These standards define certain criteria that must be met in order to facilitate the use of products from various manufacturers.
ANSI is the American National Standards Institute. Together with the ASME (American Society of Mechanical Engineers), they have developed and published a standard for flange connections. That standard is ASME/ANSI B16.5.
There is also a European standard that is similar, but NOT THE SAME. That standard is DIN, which is an acronym for the german translation of "German Institute for Standardization." The specific standard for pipe flanges is DIN EN 1092-1. This standard is also recognized by ISO (International Standards Organization) under ISO 7005.
SAE is the Society for Automotive Engineers. They have also developed a standard for flange type connections where the flange is separate from the components that it holds together. That standard is SAE J518. This standard is also recognized by ISO under ISO 6162.
This standard is based on using multiple bolt holes evenly distributed around a "bolt circle". There are 7 classes from 150# to 2500# with the pressure increasing as the class does. The standard includes flanges for pipe sizes from 1/2" to 24." There are a few different types of flanges
Class 150: 1/4" to 24"
Class 300: 1/4" to 24"
Class 400: 1/4" to 24"
Class 600: 1/4" to 24"
Class 900: 1/2" to 24"
Class 1500: 1/2" to 24"
Class 2500: 1/2" to 12"
These classes are referred to as "Class 150," or "150#" interchangeably.
DIN 1092-1/ISO 7005
This standard is very similar to ANSI. These flanges are referred to with a "DN" (for Diameter Nominal) followed by size in mm, followed by "PN" (for Pressure Nominal) followed by presure rating in bar. There are 19 sizes from 10 to 2000 and XX pressure classes from 2.5 to 100 bar
example: DN 100 PN 16
Round Flange Types
Both of the standards just mentioned have many different types within them. These types include different mating face styles. The most commonly used on valves are RF for "raised face" where there is a slightly raised inner ring arounf the valves port. Flat faces, counter-bore, o-ring groove, and other styles are available but uncommon in most industries.
There are also various styles that attach to pipes differently. That has no affect on the valve ends. The flanges on the valve are usually part of the valve body itself. They mate up with a matching flange that must be attached to the pipe. That is usually accomplished with welding, and less common with threading.
This standard is based on using 4 bolt holes located on the corners of a rectangle. There are 2 classes, Code 61 and Code 62. The flanges can be split into 2 halves known as "split flanges", or as a single piece which is called "captive."
SAE J518-1 Code 61 (ISO 6162-1): 3000 psi, 1/4" to 24"
SAE J518-2 Code 62 (ISO 6162-2): 6000 psi, 1/4" to 24"
[ SAE J518 Flange Dimensions ]
The valve has a flanges with bolt holes used to bolt it to matching flanges on the pipe. Flanged connections make removal and replacement easy. Flanged connections are common on larger valve sizes. Gaskets must be used where these flanges mate.
Lugged style flange connections are similar to wafer with 2 minor differences. 1) The lug holes ARE threaded and there is a lug hole for every bolt hole on the flanges. 2) each threaded hole accepts 2 bolts, one from each flange on opposing sides. This type of connection can be used for dead-end service, where there is only a flange on one side of the valve and the other is open to atmosphere, provided that the seat/retainer is bolted in place.
Wafer style flange connections are typically reserved for butterfly valves due to there slim profile. They can, however, also be found on ball valves from some manufacturers. This connection type simply sqeezes the valve between 2 flanges using long bots or threaded end rods. There are holes on the valve for the bolts to pass through, which are NOT threaded, and are oversized, allowing for some play. There is NOT always a hole for every bolt hole on the flanges. They are simply used to help hold the valve in place until all of the other bolts are in. On resilient seated butterfly valves, the resilent seat is also used as the seal between the valve and flat-faced flange on each side. On high performance butterfly valves, raised face flanges are used along with gaskets to form a fluid tight seal. This type of connection is NOT suitable for dead end service.
Also referred to as Tri-Clover, T-clamp, or Sanitary Clamp. These connections use a hinged clamp that tightens around the flanged ends and squeezes them together with a gasket in between. The squeezing force is created by the wedge shape of the flanges being forced deeper and deeper into the wedge shaped groove in the clamp. There are various different clamp styles including two-segment single hinge (shown here), three-segment double hinge, and two-bolt high pressure.
SAE (Society of Automotive Engineers) defines a standard of 4-bolt flanges called SAE J518. They are available as split flanges (two halves as shown here), or captive where the it is a sigle piece. Split flange connections are used in high pressure applications such as hydraulic systems. The flange halves are placed around the valve's end connection which has a lip around the edge. This lip has a flat face with a channel in which an o-ring is placed. The bolts are tightened, causing the face of the valve's lip to be drawn up against the flat face of the mating surface, usually a manifold. When installation is complete, there is metal to metal contact between the valve connection and manifold and the o-ring is trapped and compressed, forming a fluid tight seal.
There are 2 classes of these 4-bolt flange standards:
Code 61: 3000 psi, from 1/2" to 5"
Code 62: 6000 psi, from 1/2" to 2"*
* there are industry standards up to 3" that are not part of the SAE standard
This type of connection is typically found on water lines in residential plumbing. They do not require heat like soldered or welded connections making them perfect for installation in places where the use of such would be difficult or dangerous. The connection uses 2 pieces in addition to the valve and pipe. They are the ferrule (sometimes called an olive or sleeve) and a compression nut. The Compression nut is slid onto the pipe with the threads facing where the valve will be. Then the ferrule is slid onto the pipe. If the ferrule is not symmetrical, the longer side should be toward the valve. Next the pipe is inserted into the valve and the compression nut is tightened. Tightening this nut forces the ferrule into the valve stub which is tapered on the inside. Since the ferrule is made of a softer metal than the nut and valve, it gets compressed around the pipe. It also gets compresed between the valve and compression nut, forming a fluid tight seal.
Push-to-connect connections are mainly used in residential and commercial plumbing. Originally developed for fittings such as tees, elbows, and couplings, these connections can also be found on valve ends. These innovative connection types allow quick and easy connection of the pipe(s) to the valve. There is an o-ring inside the valve port that is slightly smaller than the outer diameter of the pipe to be connected. When the pipe is pushed in, the o-ring gets stretched around the pipe and compressed between the valve body and the pipe. There is a grab-ring with teeth that dig into the pipe and prevent it from being removed. The pipe can be easily removed by pressing the release ring in which retracts the teeth of the grab-ring.
Barbed hose connections are a simple and fairly primitive way of connecting soft hose ends to a valve. They are commonly found on low presure systems including air lines for an aquarium. The valves have long end connections that have barbs on them. The hose gets stretched over them when inserted and due to their shape go on far more easily than they come off. In many case this is a sufficient connection as-is, however, a hose clamp can be used to strengthen the connection if needed.
Union connections employ a female threaded collar nut that threads on to a male threaded end connection of the valve. Typically union connections fasten stubs of another connection type, like welded, glue, or threaded, onto the valve. Those connections then are attached to the pipe. Once installed, the valve body can easily be removed from the pipe using the threaded union connections. This connection type allows for fast and easy removal of the valve for cleaning, replacement, or repair.
Our P2 and PTP series PVC ball valves feature true-union connections and come with both NPT female and glue socket connections. They also feature the Dual-block locking system that prevents the threaded collar nuts from loosening due to vibration.
Manifold-mount valve connections incorporate a flat face with recessed o-rings around the ports. Bolts are used to hold the valve in place on the mating surface of the component upon which it is being mounted. The ports on the valves align with ports on the component. When the bolts are tightened, they press the 2 faces together, and compress the o-rings to form a seal between the matching ports. A common example of this type of connection is a NAMUR solenoid valve which are commonly used to attach solenoid valves to pneumatic actuators.