WHAT IS A VALVE?A valve is a device that regulates the flow of gases, liquids or loose materials through an orifice, like a pipe, by opening, closing or partially obstructing a port or passage.
HOW DOES A VALVE REGULATE THE FLOW?-blocks the flow: on/off function (gate valves, globe valves, ball valves, butterfly valves, plug valves)
-controls the flow: globe valve, butterfly valve, ball valve, plug valve
- stops the flow: directional flow (check valves)
MAIN TYPES OF VALVES
MAIN STANDARDS AND CERTIFICATION ORGANISATIONS
-API (AMERICAN PETROLEUM INSTITUTE)
-ASME (AMERICAN SOCIETY OF MECHANICAL ENGINEERS)
-ISO (INTERNATIONAL ORGANIZATION FOR STANDARDIZATION)
-DIN (DEUTSCHES INSTITUT FUR NORMUNG)
- DIN475,DIN477,DIN3202,DIN3230,DIN 3352,DIN3356,DIN3357
Material clasification generaly reffers to the body material of the valve, which can be of plastic, bronze, cast or ductile iron, carbon steel, alloy steel, stainless steel and exotic materials, high and super high alloys.
-it is used primarily in the chemical industry and not only
-main types are vinil chloride (pvc) and chlorinated polyvinyl chloride (cpvc)
-the oldest material used
-maximum temperature: 260°c
-relatively small production costs
-only for low pressures and temperatures
-high corrosion resistance
-generally it is not subject to reconditioning
GREY CAST IRON AND DUCTILE IRON
-brittle and limited to low pressures (maximum 230°c)
-not suitable for low temperatures and cryogenic environment
-difficult to weld
-except for high dimensions it is generally not subject to reconditioning
– WCC, WCB, A105
- basic material for industrial valves
- ductile, resistant, easy to cast
- temperature: -29°c + 540°c
- moderate costs, easy to weld
LOW ALLOY STEEL
-cast types : WC6,WC9,C5,C9
-forged types : F11,F22,F5,F9
-maximum temperature: +649°c
-it requires heat treatment post-welding
-high corrosion resistance in almost all chemical environments
-excelent for cryogenic applications, easy to process and weld
EXOTIC MATERIALS, HIGH AND SUPER-HIGH ALLOYS
-monnel, titanium, hastelloy, inconel
-high resistance to volatile chemical substances, high temperatures and pressures
-very expensive and difficult to process and weld
The valve seat is exposed to the working environment or fluid and can be made of a different material than the body, having a higher corrosion resistance.
The seal is divided into two types:
-soft seal: elastomeric polymers (ptfe, epdm) or plastic elastomers (teflon)
-metal/metal seal: bronze or stainless steel
- they are usually used between the set parts of the valve situated outside the pressure areas
- can be made of rolled steel sheets, graphite sheets, teflon (ptfe), stainless steel with graphite or ptfe
-they are usually used between a set and a moving part of the valve, or between an exterior part and an operating component like the stem
-can be made of graphite or teflon
Operating devices are attached to the valve and are driven by an exterior source used to adjust the valve into the desired position.
Basic cateogires are: manual actuators (with gear-box), electric, pneumatic, hydraulic and electrohydraulic.
Manual actuators are operated by using a hand wheel or a lever, they do not need an outside power source and are used in low risc environments.
Electric actuators work with dc voltage or ac voltage uniphased and triphased. When the motor receives a signal it acts upon a gear that adjusts the valve into the desired position.
Pneumatic actuators ar devices that transform the potential energy of a compressed gas, most frequently air, into mechanical energy. Frequently used types include pneumatic cylinders with simple or double effect, rotary actuators and membrane actuated elements.
HYDRAULIC AND ELECTROHYDRAULIC ACTUATORS
These devices are recommended to be used in applications that require high torques combined with easy implementing of safety regulations and high precision control.
There are four types of connections: threaded-ends, socket weld, butt-weld and flanged (plate,raised face, ring type joint).