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