What is a valve?
We can control the liquid flow or gas flow in an industrial process with the help of a valve. It would do this by different methods such as closing, opening, or blocking various passages in a pipe system. So this device can control the flow and pressure in a system, these valves are utilized in an industrial piping system that conveys liquids, gases, slurries, vapors, etc. In many industries, valves are used to control the flow, pressure, and also direction of the fluid. A valve is capable to open, close, or regulate the fluid flow in a process, these valves consist of a moving part that would open, close, or obstruct partially one or more passageways.
What are the major functions of the valve?
- Valves would control the process or isolate the part of the pipeline by opening and closing.
- It would allow more or less fluid to flow by varying the flow rate
- It would redirect the flow from one line to the other in a pipeline
- It would provide unidirectional flow
- Fluid pressure reduction
- It would keep the pressure in a pipeline or in a tank below a fixed maximum
- It would prevent accidents in an industrial process by relieving the overpressure in a container or in a pipeline.
What are the major parts of the valve?
This can be considered as the outer casing of the valve and the valve body consists of internal trim. This is the part of the valve where the fluid passes and it should be able to handle the flow pressure.
This part would act as a valve body cover, this part is bolted into the valve body. It would mostly cover the hole in the valve body, this would hold everything together inside the body
Trim is the name given for the replaceable parts of the valve-like disk, stem, Seat, and also the sleeves which are used to guide the stem.
- Disk – It is also known as valve member usually it is a movable obstruction inside the body that would restrict the flow through the valve
- Seat – it is also known as seal rings is the interior surface of the body and it would contact the disc to form a leak-tight seal.
A valve stem would transfer the input which is given to the handle to the disc, the input would be a handle motion.
This part would operate the stem and the disk, the actuator could be manually operated or motor operated.
The major purpose of this part is to prevent leakage between the bonnet and the stem. This would act as a protection between the internal part of the valve and the outside.
How to select a valve?
- It must be selected according to the flow direction and characteristics
- Valve size and trim size must be considered
- It should be selected according to the leakage class
- Construction material
- Packing and bonnet type
- Operating temperature
- Actuator type
- It must be selected by considering the fluid properties
- End connection type must be considered like flanged, screwed, etc.
- Capacity – Cv value should be considered
- Single seated, double-seated, sliding stem type, etc.
- Plug type must be considered like V ported, contour, etc.
What are the major types of valves?
The isolating valve can be used in a process system to stop the process media to a given location, it is mostly used for safety purposes.
This type of valve is used to control the flow of the fluid by varying the size of the flow passage. This would be useful to control the process quantities such as pressure, temperature, and liquid level.
Gate valves can be used for underground installations, these valves can be fully opened or fully closed. It would prevent the fluid hammer due to its slow operation process. These valves are used in pipelines as isolating valves. These valves are used when a minimum pressure loss and also when the free bore is required.
Advantages of gate valve
- Good shutoff characteristics
- Minimal pressure loss
Disadvantages of gate valve
- These valves won’t open or close quickly
- Large space is required for its installation
- Maintenance of the valve seats would be difficult
Applications of gate valve
- It can be used for high temperature and high-pressure applications
- It is also used for ON-OFF applications
This valve uses a hollow ball to control the flow these valves are quarter-turn valves. These valves would be open when the ball’s hole is in line with the flow.
Advantages of the ball valve
- It can be easily operated
- It can be used for high pressure and high-temperature applications
- Durable and reliable
Disadvantages of the ball valve
- It can’t be used with slurries because it could be jammed due to the suspended particles
- In a closed position these valves trap water in the center cavity, this could lead to crack while ice forming
Applications of ball valve
- It can be used with corrosive fluids and slurries
- Flow and pressure control of liquids and gases
These valves would have cylindrical or conical tapered plugs and this can be rotated to control the flow through the valve. These valves are mostly used to do the full flow service where quick shutoff is needed. These valves are used for steam, water, oil, gas, and chemical liquid services.
Advantages of plug valves
- Easy to open and close
- Minimal resistance to flow
- It can be serviced in place
Disadvantages of plug valve
- Great force would be required to actuate because of high friction
- Reduced port because of the tapered plug
- Air, gaseous, and vapor services
- Oil piping systems
- Coal, slurries, mud, and sewage applications
These valves are used to regulate the flow in a pipeline, it is composed of a movable disc and a stationary ring seat. These valves are used to start, stop, and regulate the fluid flow by opening and closing the passage of flow. These are linear motion valves, and it consists of a disc, valve stem, and handwheel.
Advantages of globe valve
- Throttling feature
- Fast opening and closing time
- It can be used for regular operations
Disadvantages of globe valve
- Higher pressure loss
- It would need a huge amount of force or an actuator with larger torque to close under high pressure
Applications of globe valve
- It can be used for throttling purposes
- High-temperature applications
These valves are volume control valves that are used to restrict the flow in small lines. These valves are used to provide the flow to delicate gauges where fluid pressure must be controlled.
Advantages of needle valve
- Automatic combustion control system
- It can be used for precise flow regulation
- It can be used when the flow must be gradually halted
- It can be used as on/off valves
Disadvantages of needle valve
- It can only be used with clean fluids
- It has high-pressure drop when it is open
- These valves are suitable for low flow rates
Applications of needle valve
- It can be used where accurate flow is required
- It is used with pressure pump governors
- These valves are also used for throttling and on/off services
These valves are suitable for on/off and also for throttling services, these valves are suitable for slurries and also for liquids that have suspended solid. These valves can be used with corrosive fluids because the operating mechanism is isolated from the process fluid. These valves are composed of a sleeve that is molded of rubber and a pinching mechanism.
Advantages of pinch valve
- Straight flow passage
- Process fluid won’t be in contact with the internal moving parts
- Low maintenance
- These valves can be used with contaminated fluids
Disadvantages of pinch valve
- It can’t be used for high temperature and high-pressure applications
- It is not suitable for gas media
Applications of pinch valve
- It can be used with slurries
- It can be used with liquids that have a huge amount of suspended solids
- It can be used with corrosive fluids
In this valve, the closing component of the valve is a diaphragm instead of a disc. This diaphragm would separate the valve trim from the process fluids that flow through the valve and due to this there is no need for stem gland packing. So when the actuator has turned the diaphragm which is attached to the stem would go down and close the valve.
Advantages of the diaphragm valve
- The major advantage of the diaphragm valve is that the components of the valve can be isolated from the process fluid
- It is constructed in a way that there won’t be any leakage
Disadvantages of the diaphragm valve
- Frequent maintenance would be required
- These valves are not suitable for high-temperature applications
Applications of the diaphragm valve
- It can be used with normal liquids, dirty liquids, and also with gases
- Pharmaceutical and food processing
- These valves are suitable for corrosive applications
As shown in the above image the disc would be rotated while turning the actuator. So the disc would be parallel, or perpendicular to the flow, during the flow the disc would be present and this would create pressure drop even it’s in the open position.
Advantages of a butterfly valve
- It would open and close quickly
- These valves are very precise and due to this they can be used in many industrial applications
- Less maintenance.
Disadvantages of a butterfly valve
- Some portion of the valve would be present in between the flow
- It can be used for high temperature and high-pressure services
- Vacuum service
- Chemical and pharmaceutical services
Comparison between manual valves?
|Globe||Controlling, starting, and stopping the flow||Gases, liquids, cryogenics|
|Gate||Frequent valve operation Starting, stopping, and controlling the flow||Gases, fluids with solids, vacuum, slurries, and contaminated fluid|
|Ball||Throttling, flow diversion, starting and stopping||Gas, liquid, vacuum, cryogenics, corrosive and non-abrasive slurry|
|Plug||Throttling, flow diversion, starting and stopping||Gas, liquid, vacuum, sticky fluids, corrosive fluids, and granules|
|Butterfly||Start, stop and flow control||Gas, liquid, vacuum, slurries, powder, granules, and foodstuff|
|Pinch||Start, stop and flow control||Liquid, vacuum, slurries, powder, granules, and corrosive|
|Diaphragm||Start, stop and flow control||Gas, liquids that carry solids, viscous fluid, vacuum, slurry, sludge, and hazardous fluids|
|Needle||Flow regulation||High-pressure applications|