A valve can be defined as a mechanical element that can be used to start, stop or regulate the flow of liquids or gases by means of moving parts that open, close or partially or totally obstruct one or more holes.
There are two types of valve passages:
FULL BORE: the inside pitch is equal to the pipe pitch.
(F.B.)
REDUCED BORE: the inside diameter is smaller than the diameter of the pipe. (R.B.)
The reduced bore is a way to lower the cost of manufacturing a valve.
On threaded valves - whether DIN or ANSI - the size is always expressed in inches. In welded valves, the valve size is expressed in inches followed by the thickness or type of pipe in which they are installed.
Example:
2" SW or BW for Schedule 40 pipe 2" SW or BW for millimeter pipe.
We must necessarily identify the type of pipe to which the valve will be welded. In valves that are generally installed in pharmaceutical laboratories, a type of welding called orbital welding is used. This type of welding is done with an automatic machine that does not leave burrs inside the welded joints when welding.
To select the ends of the valve, we will need the exact type of pipe; otherwise the weld will be imperfect.
SW and BW valves have a wider tolerance range when welding to the pipes. Even multi-purpose valves for various types of tubing are manufactured. The quotation marks ["] are used to indicate that the number is in inches.
To convert a measurement from inches to millimeters, you can use the trick of multiplying inches by 25, for example:
6" = 6 x 25 = 150mm
PRESSURE
When talking about pressures, we will find that valves are designed for different pressures. The design pressure is identified by the acronym PN - Nominal Pressure.
Nominal pressures (PN) are expressed in bar or Kg/cm2. Although, according to European standards, it should be in Pascals, it is not usually used in commercial catalogues. As with the diameters, the nominal pressure or PN is a nomenclature specific to DIN valves. In this small table there is a summary of the most used pressures in the design of DIN valves.
In ANSI valves we will talk about the RATING, which is expressed in pounds (or psi).
The pressure rating of a valve is the maximum pressure for which it is designed, but other factors must be taken into account if we want to work at the limit of the design pressure. The pad [#] is a widely used abbreviation for pounds.
CONNECTIONS
THREAD: We have several types of thread according to the applications and standards. The most common are:
- GAS thread (according to DIN standard)
- NPT thread (according to ASA standard)
- DIN thread (for food sector)
FLANGES: As with the thread, we also have different types of flanges that vary depending on the standard, working pressure and applications. Basically we will divide them into two: DIN and ASA (or ANSI). Within the two most used standards, we subdivide them into the following types:
- FF: flat-faced flanges, for low pressures
- RF: flanges with shoulder. They are the most commonly used
- Crazy: They are so called because they rotate on the end of the valve.
- Tongue and groove: For high pressures.
WELD: another widely used connection. The valve is welded directly to the pipe.
- SW: Type of weld where the pipe is inserted into the valve.
- BW: Type of welding where the valve is welded, as if the joint were between two pipes (see glossary of technical terms).
NIPPLES
CLAMP
Connection basically used in the pharmaceutical industry, it provides an easy and quick assembly and disassembly of the valve.
GROOVED
Type of connection in which a groove is made at the ends of the pipe in the form of a channel. The joint is made by means of a clamp with a gasket. It is widely used in pipe connections in fire-fighting installations.
This type of connection between pipes and valves has become very popular, given the lack of skilled labour for welding. It has other applications, but in industry it has not been successful.
