Whichever type of control valve is selected, they all have common features such as:
- Surfaces that form a seal to seal the passage. In control valves usually, there is a fixed seal and a movable seal.
- Control valves usually consist of a stem that allows a movable seat to move.
- A hand-wheel or similar devices to assist in the movement of the stem.
- The packing or seal that prevents fluid loss when the stem leaves the valve body.
- A conduit for passage of the fluid through the valve. The duct configuration defines the type of the control that can be expected.
Valve Categories
Due to the different variables, there cannot be a universal valve. therefore, to meet the changing requirements of the industry, countless designs and variants have been created over the years as ew materials have been developed.
All types of valves fall into nine categories.
- Gate valves
- Globe valves
- Ball valves
- Butterfly valves
- Pinch valves
- Diaphragm valves
- Plug valves
- Check valves
- Relief valves.
These basic valve categories are described below.
It would be impossible to mention all the characteristics of each type of valve that is manufactured.
Rather, an overview of gate valve, plug valve, globe valve, and diaphragm valves is presented in a general format, giving a recommendation for service, applications, advantages, disadvantages, and other useful information for the reader.
Gate Valves
The gate valve is a multi-turn valve, in which the orifice is closed with a flat-faced vertical disc that slides at right angles to the seat.
Recommended for
- Service for full opening or closing, no throttle.
- For infrequent use.
- For minimum resistance to circulation.
- For minimum amount of fluid or liquid trapped in the pipe.
Applications
General Service, oils and petroleum, gas, air, semi-liquid pastes, liquid thick, steam gases and non-condensable liquids, and corrosive liquids.
Advantages
- High capacity
- Tight closure
- Low cost
- Simple design and operation
- Low resistance to flow.
Disadvantages
- Poor flow control, Requires high force to actuate, produces cavitation with low-pressure drop.
- Must be covered or completely closed.
- Throttling position will cause seat and disc erosion.
Variations
Solid wedge, flexible wedge, split wedge, double-disk.
Body material: Bronze, cast iron, iron, forged steel, Monel, steel, cast, stainless steel, and PVC plastic.
Various components
Special instructions for installation and maintenance
Lubricate at regular intervals. correct from immediate packing leakage.
Always cool the system when closing a pipe for hot liquids and when checking that the valves are closed.
Never close the valves by force with the key or a lever.
Open the valves slowly to avoid hydraulic shock in the pipe.
Close valves slowly to help discharge sediment and trapped grime.
Specifications for the order
Type of end connection.
Wedge type.
Seat type.
Stem type.
Bonnet type.
Stem packing type.
Pressure rating for operation and design.
Temperature rating for operation and design.
Plug Valves
The plug valve is 1/4 turn, which controls circulation using a cylindrical or conical plug that has a hole in the center. The plug can be moved from the open to the closed position by turning 90 degrees.
Recommended for
- Full open or full close service.
- For frequent actuation.
- for the low-pressure drop across the valve.
- For minimum flow resistance.
- For a minimum amount of fluid trapped in the pipeline.
Applications
General service, semi-liquid pastes, liquids, vapors, gases, corrosives,
Advantages
- High capacity
- Low cost
- Hermetic closure
- Fast operation
Disadvantages
- Requires high torque to drive
- Seat wear
- Cavitation with low-pressure drop.
Variations
Lubricated, non-lubricated, multiple holes.
Materials: Iron, ductile iron, carbon steel, stainless steel, alloy 20 , Monel, nickel, Hastelloy, plastic jacket.
Special instructions for installation and maintenance.
Allow clearance to move the handle on valves actuated with a key.
In valves with lubricated plug, do it before putting them into operation service.
In valves with move lubricated, lubricate them at regular intervals.
Specifications for order
Body materials
Plug materials
Temperature rating
Orifice arrangement, if multi-orifice
Lubricant, if lubricant valve.
Globe Valves
Globe valve is a multi-turn valve, in which closure is achieved by means of a disc or plug that closes or cuts off the flow of fluid in a seat that is usually parallel to the flow in the pipe.
Recommended for
- Throttling or flow regulation
- For frequent actuation
- For positive gas or air shut-off
- When a certain resistance to flow is acceptable.
Applications
General service, liquids, vapors, corrosive gas, semi-liquid pastes.
Advantages
- Efficient throttling with minimal disk stretching or erosion or seat.
- Short disc stroke and few turns to activate them, which reduce the time and wear on the stem and bonnet.
- Precise flow control
- Available with multiple orifices.
Disadvantages
- Large pressure drop
- High relative cost
Variations
Normal (standard), “Y”, angled, three-way.
Material
Body: Bronze, iron, cast iron, forged steel, Monel, steel, stainless, plastics,
Components: various
Special instructions for installation and maintenance
Install so the pressure is below the disc, except in service with high-temperature steam, registration in lubrication.
The valve must be slightly opened to expel foreign bodies for the seat.
Tighten the packing nut, to immediately correct leaks for the packing.
Specifications for the order
End connection type
Disc type
Seat type
Stem type
Stem packing or seal type
Bonnet type
Pressure rating
Temperature rating
Diaphragm Valves
Diaphragm valves are multi-turn valves that close by means of a flexible diaphragm attached to a compressor. when the valve stem lowers the compressor, the diaphragm seals and cuts off fluid passage.
Recommended for
- Service with total opening or total closure
- For throttling service
- For service with low operating pressures
Applications
Corrosive fluids, sticky or viscous materials, semi-liquid pastes fibrous, sludge, food, pharmaceutics.
Advantages
- Low cost
- No packings
- No chance of stem leakage
- Immune to ducting problems, clogging, corrosion, or gum formation in circulating products.
Disadvantages
- Diaphragm susceptible to wear
- High torque when closing with the pipe full
Variations
Type with weir and type in a straight line.
Materials
Metallic, solid plastics, with jacket, in a great variety of each.
Special instructions for installation and maintenance
Lubricate at regular intervals.
Do not use bars, key or tools to close it.
Specifications for the order
Body material
Diaphragm material.
End connection.
Stem type.
Bonnet type.
Actuation type.
Operating pressure.
Operating temperature.