Butterfly valves are valves characterized by a disc shutter that rotates around an axis perpendicular to that of the pipe on which they are installed and act. They are used in many aspects:
- Aqueducts: they are used for interception by exploiting the main characteristics of this type of valve. In fact, being small in size, they make it possible to reduce overall dimensions compared to the classic gate valves that are normally used in this field.;
- Positive ignition engines: it is used both in the carburetor to regulate the air flow and in the injection unit to regulate the flow rate of the mixture. However, they have the disadvantage of generating significant pressure drop and other systems are sometimes preferred.
Wafer valves are a particular configuration of butterfly valves with four centering ears obtained by casting the valve body.
The components of the wafer valves
Wafer valves have a number of components required for proper operation:
- Valve body: represents the bulkier part and the support of the whole component. Usually made of spheroidal cast iron, carbon steel or stainless steel exploiting both the resistance characteristics and the corrosion resistance.
- Seat: made of elastomeric material and is necessary for sealing to avoid pressure or flow losses.
- Disc: it is the rotating element that acts as a shutter when the valve is closed and is also made of the same materials as the valve body.
These are the main components of the valve but there are also an underlying flange and the shaft that are made of the same materials as the disc and the valve body. It is important to note that corrosion resistance is the main requirement and various methods are used for protection such as paints based on epoxy powders. All materials must have organoleptic, chemical, physical and biological characteristics such as to comply with health regulations because they come into contact with fluids for human consumption.
The characteristics of wafer valves
Wafer valves are valves which, as seen, act by rotating the disc. Intermediate positions, however, generate pressure drops and inefficiencies and, for this reason, it is preferred not to use them for flow regulation but only in the two main configurations. Usually a clockwise closing is chosen for design reasons but there may also be an anticlockwise closing if appropriately specified on the supply.
Numerous construction possibilities can be envisaged for the closure:
- Manual: if the diameter is small, a handwheel or lever can be used to force the closure;
- Demultipliers: with larger diameters or important pressures, it is necessary to use devices;
- Bypass: used to force closure by programming the pressure that is established on the two different faces of the closure disc.
Regulations and markings of wafer valves
Wafer valves, to be introduced on the market, must comply with some important certifications:
- UNI EN 10204 3.1: it is a type of certification that certifies that the manufacturer has made the product according to the customer's specifications. In fact, this certificate summarizes the characteristics of the materials used, the results of tests carried out by a department independent of the factory, heat treatments and other properties.
- UNI EN 12266-1: it concerns the specifications and characteristics of the pressure tests, as well as the acceptance criteria of the same.
- UNI EN 1074-1, 1074-2: establishes the criteria to be followed in the design, testing and installation of components that transport water intended for human use.
Compliance with these standards is a fundamental requirement for the certification of the product and, in this specific case, of important components such as wafer or butterfly valves.
The marking of the wafer valves
The marking, that is the identification code of each individual product, must have some standard characteristics for wafer valves: in fact, the nominal diameter, the nominal pressure, the material of the valve body, the name of the manufacturer and the year of production must be present (not the year of implementation) and, finally, the reference regulations which are those described above. This code allows you to uniquely identify each component in the event of damage or breakdowns, speeding up troubleshooting operations.
The materials of the Wafer valves
Wafer-type valves, the operation of which has been described in the previous paragraphs, are made up of different components and have materials of a different nature, but essential for obtaining the characteristics that make these valves so important within the systems in which they are installed:
- AISI 316 stainless steel: formability and corrosion resistance are the two main characteristics of this type of steel, allowing it to be used even in particularly aggressive environments. The weldability and the solubilization heat treatment allow both to obtain particular conformations in operation and to further improve the characteristics seen. This steel is used in wafer valves for the body, the flap, the rod, the spring, the stop and the grain.
- PTFE: it is a polymer with exceptional characteristics for chemical resistance, non-stick (used for this for non-stick cookware), thermal resistance and resistance to friction. It is used for making the washers inside the wafer valves.
- FKM: these are fluorinated elastomers belonging to the class of technopolymers. The high chemical resistance distinguishes them from other types of rubbers, while the thermal resistance depends on the degree of vulcanization. This material is suitable for making caps and gaskets.
The combination of these materials, in conjunction with skilful design, helps to create qualitatively excellent products by improving the safety and efficiency of the systems.
Additional information to consider for wafer type valves
In addition to all the previously analyzed characteristics, it is necessary to evaluate other properties that can influence both the choice and the use of these valves.
- Pressure-temperature rating: these are curves that show the temperature on the abscissa (X axis) and the pressure on the ordinate (Y axis). Furthermore, there is a dependence on the nominal diameter of the passage;
- The tightening torque: that is the torque (N*m) to be applied in order to be able to carry out a correct locking in the presence of the threaded connection. In particular, we start from a torque of 4 or 5 Nm for DN15 up to 85 or 95 Nm for DN100;
- KV value: quantity of cubic meters of water passing through the valve generating a pressure drop in bar.
- Pressure drop diagram: shows the flow rate in cubic meters per hour on the abscissa, while the pressure drops are on the abscissa. Furthermore, these curves are dimension dependent.
- Minimum opening pressure: it is the pressure required to allow the valve to open and depends on whether or not there is an opening spring.
The choice of all these parameters is essential to consciously evaluate in relation to the specific system of interest. Neglecting even just one of these aspects can lead to critical issues in operation that compromise the operation of the system itself, with more or less serious consequences for the connected rooms or persons.
