This basic document follows the humble purpose to offer a first introduction to the ample world of industrial valves. It is therefore a useful tool for beginners and new personnel joining one of the hundreds of thousand industrial and fluid control Organizations around the world.

In the ancient Roman Empire and Islamic period, primitive valves made out of stone were already used to stop or divert the water flow for human utilization. Nevertheless, the definite presence of valves as we know them today are rooted back to the first industrial revolution with steam as motive force to make machines to operate. The XX century drew the takeoff of valves as modern engineering equipment contributing to the development of the industrial world. No modern society could be figured out without the use of valves to assist in all manufacturing services.

In a very rough concept, hydraulic systems are comprehensive of three main blocks: Pumps excising the needed pressure to move fluids, Pipes transporting these fluids and Valves controlling these fluids. All other components are part and sophistication from these major ones.

How valves could be defined?

Mechanical devices for controlling fluids in the piping system. The CEN (European Committee for Standardization, in their English acronym) EN -736-2 defines valves as any piping component which is operating on fluids by opening and closing, partially throttling or deviating the fluid.

Irrespectively of the valve style, there are common components, which are following a similar functionality on valves. These are listed underneath a typical valve style (globe valve):

We might classify Valves according to their purpose into the following main categories:

1. Isolation: Devised to stop the full flow rate across the pipe whenever required.
2. Non-Return: Devised to prevent the flow return to the pressurized side.
3. Throttling: Devised to partially closing the valve thus reducing the flow, deviating and / or mixing it manually, remotely or self-fluid acting.
4. Safety: Devised to protect personnel and equipment against the overpressure hazards.

Also called Stop Valves, Block Valves, Shut off Valves given the purpose within the flow control system. This valve style can also be sub-categorized into two categories upon the stem operating movement:

The linear isolating valves are feature by a vertical movement of the stem and closing element; downwards for closure and upwards for opening action. These are Multiturn operated and featured by a gradual and slow operation. This is an essential design when handling compressible fluids such as steam and vapours that might jeopardize the system by fluid phenomena caused by a quick closing action.

The Rotary valves shall be featured by turning the valve stem for opening or closure. They are quick operation valves and are usually suited to non-compressible fluids such as water and other low-pressure media. The operation mode is by hand lever or worm gear in case of choosing a slower operation.

Within the segment of linear isolating valves, the most common types are Globe valves (including the variants such as bellows sealed type), Gate Valves (including variant styles such as Knife gate, slab gate, penstocks..),  and diaphragm valves.

(Refer to the final chapter “Glossary and definitions”).

Within the segment of rotary isolating valves, the most common types are butterfly Valves, Ball Valves and Plug Valves.

(Refer to the final chapter “Glossary and definitions”).

Another common classification of the isolating valve styles is determined by the mode of operation of the valves as follows:

• The manually operated valves are the simplest style as they are manned by the plant operator thus the valves should be placed at reach and not requiring too often operation cycles.
• The self-operating valves are operated by the same line flow exerting the thrust onto the closing element given a determined set parametre (temperature, flow rate, pressure..).
• The auxiliary powered valves are those requiring the external input of motive media such as air (pneumatic), electricity (electric), liquid (hydraulic) and are typically used on repetitive processes, non-easily accessible points ad where a good process accuracy is required. This sort of valves led the way to the industry 4.0 as we know it today.

Non Return Valves are self-acting flow control elements that prevent the return of the flow to the pressurized side of the system. They are unidirectional valves, with the disc opening flow wise and closing counter wise. (Always observe the installation instructions in our Operating Manuals).

There are diverse Non-return valve styles depending on the construction design:

1. – Swing Check Valves.
2. – Tilting Swing Check Valves.
3. – Dual Plate Check Valves.
4. – Spring-loaded check Valves.
5. – Ball Check Valves.
6. – Flexible lip check valves.
7. – Piston type check valve.

Generally speaking and provided that all valves perform the same purpose, the right choice of the valve style is based on the user criteria, for example end connections, materials, inner gaskets, pressure drop level, pressure rating and the fluid state (viscosity, temperature..). Consult in our “Products” section the specifics of each check valve.

Throttling valves, so called control valves are those intended to modify the flow rate in a System. The most common ones are those requiring the use of an external input (electric or pneumatic in example). Control valves are the end element in the flow control system and are used on frequent and accurate control operations. Not all throttling valves are externally operated, in example a manual globe valve provided with a profiled plug is also regarded as such. However self-operating valves should be regarded as ON/OFF valves since the stem and plug element are not performing intermediate positions.

Control Valves cannot be analyzed without the concept of the control loop. The control loop is comprehensive of an end valve, positioner, PID (electronic regulator) and sensing instrument.

How does it work?: the parameter to be controlled is set into the PID (electronic controller), the actual parameter sensed at the system is transferred to the PID which interprets the values reacting by sending an electronic signal to the valve actuator or electro pneumatic positioner which in turn instruct the valve for opening or closing movements. The change of valve state will subsequently cause a change in the process system where the sensor placed downstream will newly emit sensing parameters to the PID for new actions in the loop.

Control valves can be designed in straight through pattern but also in three ways for flow deviation or mixing. Mixing valves are devised to act onto two different fluids at the valve inlet ports to get a single fluid at the third valve outlet port. Diverting Valves are devised to act onto a single fluid at the valve inlet port to get a the fluid diverted throughout the other two valve outlet ports. The image below illustrated the plug configuration upon the valve style.

Nuestro Modulo M-4 analiza con más complejidad las Válvulas de control, para más detalles acerca del mismo puedes indicarnos tu interés o lanzarnos tus consultas a nuestro buzón de formación.

Safety and Pressure Relief Valves are self-acting devices that prevent overpressure from pressurized vessels. These valves are typically built in a 90 º angle design to better blow the fluid off the system. They are spring loaded, the spring is set to a determined rate above the system pressure according to the Rules above which the valve lift will blow off relieving the excess fluid until the pressure is restored to the acceptable in the system.

Safety valves are of essence in closed pressurized vessels where the rise of pressure of the non-compressible fluids would cause an outburst of the vessel with affection to people and property damage.

There are diverse valve styles (spring loaded, balanced, pilot operated, weight loaded..), with diverse constructive styles (open bonnets, closed bonnets, gastight cap, semi nozzle, full nozzle..) to satisfy diverse design codes (ASME Sec. VIII, ASME Sec. I, API 2000, TUV TRD-421..).

Existen diversos tipos de Válvulas de seguridad diseñados bajo diversos códigos para satisfacer las necesidades de la industria actual.

Globe Valves:

Valves with a weir body design to favour the flow circulation, with a closing disc seating on to a precisely machined seat ring that ensures the tightness. They are unidirectional valves with flow inlet underneath the disc, which is the closing element of the valve. The atmospheric sealing is ensured with packing rings around the valve stem.

Bellow Sealed Globe Valves:

These Valves are based on the same concept design of globe valves but with the additional performance of having a metallic bellows around the stem that ensures the atmospheric tightness by the non-wearing out soft packing.

Balanced Globe Valves:

They are throttling globe Valves performed by having upstream and downstream measuring inlets for gauges for reference in adjusting the right valve flow.

Gate Valves:

A wedge sliding through two parallel discs to ensure the closure features these Valves. These are high capacity valves and bidirectional though not too suited to perform throttling duties.

Knife Gate Valves:

These are a variant of gate valves with a plate sheet with edgy ending to cut through the viscous fluid. Unlike conventional Gate Valves, these are unidirectional and are designed to be installed between flanges in wafer or lug type.

Diaphragm Valves:

These are isolating Valves featured by performing the closure through a flexible and deformable elastic diaphragm, which is actioned by a compressor linked to the bonnet assembly. They are bidirectional valves, are open with the diaphragm in a concave position, and closed in convex position. There are two typical styles,. Weir and straight-out type for election upon the fluid and application.

Butterfly Valves:

Valves with a circular disc, which is turned by the stem, leaving the free passage when the stem is in parallel and blocking the flow when it is perpendicular. The disc turns 90º allowing the flow to pass or blocking it. These are bidirectional valves in essence. The term “Butterfly” comes by the popular similarity to a butterfly and its wings represented by the stem and the two disc sides.

There are diverse butterfly valve types depending on the stem design: concentric, eccentric and triple offset. A well detailed information about working principle and limits of use and application can be found in all our product manuals available in this web site.

Ball Valves:

Valves with a perforated ball as closing element, which is turned by the stem, leaving the free passage though the ball and blocking the flow when the ball perforation is turned from the ends inlet and outlet. The handle position provides an instant visual indication. When handle is aligned to the valve ports, it is an indication of open and when the handle is turned in angle to the valve ports indicated closed.

There are also diverse types of ball valves upon the combined position of the stem and the ball; floating ball valves being the most common type, the stem exerts the movement of the ball by the upper part whereas the trunnion type is that one with the ball guided by the upper and down the ball. This is the most typical design in large size units.

Plug Valves:

Plug valves are a variant of ball valves and are featured by a perforated plug as closing element which is turned by the stem, leaving the free passage though the plug when this is aligned to the pipeline. The plugs can be lubricated or sleeve type.

Notes:

Information that is more specific will be available in other sections of this web site as follows:

• Products: Precise definitions and comprehensive guide of use on each and all of our products.
• Operating and Installation Manuals: Available through the After Market and Products sections. They are defining the essential safety instructions and limits of use.
• Useful information: Material compatibility versus fluids.

Our Blog entries are another typical source of good tips for use of valves and applications. Do not miss to follow it.

Our specialists are available to answer your questions; there is a mailbox for this specific purpose formacion@comeval.es or simply drop us your request through the contact formularies appearing in all diverse sections of this site.

Also specific training modules on diverse topics and levels are available to be attended, our training team is regularly updating the programme, a current list of regular modules can be also read in this section.