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WORKSHOP PRACTICE
A valve is a device that regulates the flow of a fluid (gases, fluidized solid, slurries, or
liquids) by opening, closing, or partially obstructing various
passageways.
industrial, military, commercial,
residential, and transportation.
Oil and gas, power generation, mining, water recirculation,
sewerage and chemical manufacturing are the industries in
which the majority of valves are used.
It can be operated manually, either by a hand wheel, lever or pedal.
It may also be automatic, driven by changes in pressure, temperature or flow.
It can be classified either:Manual
SolenoidHydraulic/Pneumatic
Safety codes Pressure and temperature must never exceed the limit
Proper place Proper type of seal/gasket Proper flanged alignment
Gate Valve Poppet Valve Plug Valve Globe Valve Check Valve Butterfly Valve Diaphragm Valve Ball Valve Needle Valve Pinch Valve
Body and Bonnet Ports Disc Seat/seal Stem Bonnet Spring Handle Gland Follower Gasket
Bonnet is the part of a valve casing through which the stem passes and that forms a guide and seal for the stem. It hold the fluid going through the valve.
Valve bodies are usually metallic. Brass, bronze, gunmetal, cast iron,
steel, alloy steels and stainless steel are very common. Plastic bodies are used
for relatively low pressures and temperatures. PVC, PP, PVDF and glass-reinforced nylon are common plastics
used for valve bodies.
To allow the fluids in and out of the valve. These ports are
obstructed or opened up by the valve member or disc to
control the fluid flow.
Inside the valve body, flow through the valve may be partly or fully
blocked by an object called a disc.
It comes in various shapes. Although the valve body remains stationary within the fluid system, the disc in the valve is movable so
it can control flow.
The valve seat is the interior surface in the body which contacts or could
contact the disc to form a seal which should be leak-tight when the valve is
shut.
Seats can be integral to the valve body, that is "hard" metal or plastic. Nearly all metal seated valves leak, even though
some leaks are extremely small.
The stem is a rod or similar piece
spanning the inside and the outside of the valve.
It is to control the internal disc or rotor from outside the valve.
A bonnet acts as a cover on the valve body. It is commonly semi-
permanently screwed into the valve body.
The bonnet is attached to hold everything together inside. To
access internal parts of a valve Many valves do not have bonnets
ex. plug valves
Many valves have a spring for spring-loading, to normally shift the disc into some position by
default but allow control to reposition the disc.
It is to open and closed the valve and to control the flow of fluids.
It is to prevent any leakage of fluid while allowing the stem to move.
To prevent leakage of fluids from the moving parts.
One-port valvesTwo-port valvesThree-port valvesFour-port valves
It can only allow the fluid or gas to move along the pipe or they
can stop it from moving. Depending on the valve chosen, the speed on which this is done
may too be changed.
Not allow to direct a fluid or gas in a specific pipe.
2-way valves are made in which the flow can go in either direction between the two ports, when a valve is placed into a certain
application, flow is often expected to go from one certain port on the upstream side of the valve, to the
other port on the downstream side.
The flow coming in at one port can be directed to either the
second port in one position or the third port in another position or in
an intermediate position so all flow is stopped.
3-way valves are ball or rotor valves
It has four ports equally spaced round the valve chamber and the plug has two
passages to connect adjacent ports. It is operated with two positions.
It can be used to isolate and to simultaneously bypass a sampling
cylinder installed on a pressurized water line.
It is useful to take a fluid sample without affecting the pressure of a hydraulic
system and to avoid degassing
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