Gate valve function
The gate valves are mainly used to allow or not to pass a fluid (ON-OFF) and are not designed to regulate it, which indicates that they must be completely open or completely closed so that their interiors (seat and wedge) are not worn out prematurely by the fluid and its pressure and thus prevent leakage.

The gate valves are bidirectional and full-pass, they can also be with fixed stem or outgoing stem according to the spaces that are available in the lines for installation.

Gate valves are also called sectioning and are manufactured in various materials such as: bronze, cast carbon steel, stainless steel, iron, forged steel, PVC, CPVC with threaded ends, flanged, butt weld, butt weld, weld able to box (socket Weld).

Gate valves are used very often due to their easy accessibility, in addition to being an economical option among others to cover general services but they are also an option in handling aggressive or corrosive industrial fluids once their operating conditions have been determined (fluid- pressure-temperature).

Among its disadvantages are that they are very large and heavy which does not make installation and maintenance easy, also its closing is very slow since you have to turn a steering wheel several times to open or close completely. They can be operated in addition to a steering wheel, a gear operator, and pneumatic and electric actuators.

What are gate valves and how to choose them correctly?

There are many situations in which we may need to use gate valves, but in order to choose them correctly it is necessary to understand what they are, what they can be used for and what types of them exist. We reveal all the unknowns in this article.

Basic definition of gate valve

A gate valve is a tool whose function is to raise or open a gate or blade to allow the passage of fluids. These gates or blades can be round or rectangular. They have a seal that is achieved by placing a disk in two distributed areas. The faces of the latter can be parallel or wedge-shaped.

How a gate valve works

The gate is usually closed. When the valve is open, the gate is placed in the excess of the valve, which leaves an opening of the same size as the pipe in which it is installed, although there are full-pass and restricted-pass valves.

In which cases is a gate valve used?

As a rule, gate valves are used when there is a need for a rectilinear flow or a minimum restriction of the passage of the gate.

What types of gate valves exist?

They are usually classified in valves with ascending and non-ascending stem. The former are used when it is important to quickly know the state of the same, that is, if it is open or closed in case the rod and the gate can be damaged due to the contaminating or corrosive fluids that pass through it.

Advantages of using gate valves

One of the things that is important to note about gate valves is that they offer greater capacity than other options. Apart from this, they are very economical tools if you compare the ratio of benefits they offer. They are easy to handle because their design and operation have been designed for this.

In summary, gate valves:
  • They have a high capacity
  • They have a very efficient seal
  • They are economical
  • They offer a very simple operation
  • They offer little resistance to circulation

Disadvantages of using gate valves or in what situations it is not convenient to use them

The use of gate valves is not recommended when our purpose is to throttle. Nor when we need a water flow very easy to handle or when our intention is to have a regulation tool.

In summary, the main disadvantages are:
  • They are not efficient controlling circulation
  • Produce cavitation with low-pressure drop
  • It must be open or closed completely
  • It takes a lot of force to drive it
  • They should not be used for strangulation purposes

In the tasks and tasks carried out in the industry, the correct selection and application of the valves is of vital importance, as well as, their functionality is for this reason that the basic operation of a gate valve must be known.

What is a gate valve?

- Gate valves are valves that are responsible for opening or lifting a gate or blade to allow the free passage of fluids.
- The gate valves are differentiated by having a seal, which is achieved through the seat of the disc in two distributed areas.
- The gate or blade can be round or rectangular.
- The faces of the disc can be parallel or wedge-shaped.

When to use a gate valve?

The gate valves are used when a rectilinear fluid flow is necessary, as well as a minimum restriction to the passage thereof, the gate valves owe their name to the piece that blocks or allows the flow passage, it is a gate.

Characteristics of a gate valve

The gate is usually a wedge, when the valve is wide open the gate is completely located in the excess of the valve, this leaves an opening in the valve for the passage of fluid of the same size of the pipe in which it is installed (full-pass and restricted-pass gate valves exist), therefore there is little pressure drop or restrictions through the valve.

Types of valves: classification and its functions


Valve Classification

There are two main methods used to classify valves. These include the control method and the function of the valve. Most valves are classified in one or more of the following classifications. It is important to understand how the valve works, as well as the best way to use it, to reduce the need for maintenance of the valve and the additional wear of its parts.

Control Methods

The mechanism that the valve uses to control the flow depends on the type and location of the closure element in the valve body. In general, there are two methods to control the flow through a valve.

Linear Motion Valves

They use a closing member that moves in a straight line to start, stop or throttle the flow. The closure device could be a disc, ribbon or flexible material, such as a diaphragm. Linear motion valves tend to be slower in operation, but have a higher level of accuracy and stability in the position of the closing member.

The closing device can be used to:
  • Move a disc, or plug into or against a hole
  • Slide a ribbon, cylindrical or spherical through a hole
  • Move a flexible material in the flow path

The most common example of linear motion valves includes gate valves; globe valves, fixed cone valves, needle valves, and sleeve valves.

Rotary Motion Valves

These valves rotate a disc or ellipse around an angular or circular axis that extends through the diameter of a hole. They are also known as quarter turn valves. The quarter turn valves will be in their fully open or fully closed (0 °) state after a 90 ° rotation of the stem. Its operation is much faster than linear motion valves.

The most common examples of rotary motion valves include ball valves, butterfly valves, plug valves and ball valves.

Valve Function

Valves are part of many everyday machines and perform a variety of functions. The three common valve functions include stopping and starting the flow, limiting the flow (control) and acting as a check of no return for the flow (check).

Start / Stop Valves

They are used for systems that do not need strangulated flow. The valve opens to allow flow and closes to stop the flow. They are also known as on / off service or blocking valves.

These valves are often used with a hand wheel, but can be automated with an actuator. Start / stop valves are used when the flow needs to be diverted or for mixing applications when exact measurements are not required. Automatic start / stop valves are used in safety management systems to immediately shut down the system in an emergency. Some start / stop valves can be considered self-acting valves because their mechanisms operate according to the system flow without direct operator intervention.

Relief valves are also used to protect the system from excessive speed flow by closing immediately if a downstream pipe is broken or blocked. For air or gas systems, the on / off valves can be used to regulate the pressure through the pipe and protect against overpressure by allowing gas to exit the pipe.

Regulatory or Control Valves

They control the speed and capacity of flow, temperature or pressure through a system. Control valves can be moved to any position, even fully open and completely closed. They can be operated with a hand wheel or can be equipped with an automatic actuator. The actuation systems provide greater thrust and positioning capacity. Pressure regulators are responsible for varying the position of the valve to maintain constant pressure downstream. The regulator opens and closes to increase or decrease the pressure in the system.

Check Valves or Check Valves.

The flow in the desired direction opens the valve, while the flow in the opposite direction forces the valve to close. These valves are important to avoid backflow to systems in applications such as wastewater management and in process systems that have variable pressures and must be kept separate.

Types of Valves According To Their Design


GATE VALVES
Description
Linear motion valves used to start and stop the flow. The valve is fully open when the disk is removed from the flow stream. The gate valves are classified according to the type of disc used: solid wedge, flexible wedge, split wedge or parallel disc.

Advantage
  • No resistance to flow when open
  • Little pressure drop
  • Good
  • Little / no leak
Disadvantages
  • The flow changes non-linearly with the stem path
  • Vibration / cavitation when partially open
  • Subject to wear
  • Repair work is difficult

GLOBE VALVES
Linear motion valves used to start, stop and regulate the flow. The disc moves perpendicularly to the seat to open or close the flow, whereby the annular space between the disc and the seat ring gradually changes. There are three body designs for globe valves: Z-body, Y-body and angle and three designs for the disk: ball disk, composition disk and plug disk.

Advantage
  • Regulation and regulation flow
  • Less seat leaks than gate valve
Disadvantages
  • Loss of height due to changes in flow direction
  • The dynamics can create pulsations and damage the fit / packing / actuators
  • Noisy in high-pressure applications
  • The valves can be very heavy / large for a given application

PLUG VALVES
Rotation motion valves used to stop and start fluid flow. The disc is a solid conical or cylindrical plug with a boring passage at right angles to the longitudinal axis of the plug. When open, the plug aligns with the inlet and outlet port of the valve body. The caps are round or cylindrical with cone. The plug valves are easy to adapt

Advantage
  • Rotational movement
  • Suitable for multiport designs
Disadvantages
  • Typically NOT for strangulation

DIAPHRAGM VALVES
Linear motion valves that are used to start regulate and stop the flow of fluid. The disc is flexible and sealed with the seat in an open area at the top of the valve body.

Advantage
  • Very suitable for difficult environments (corrosive chemicals, sludge, radioactive fluids)
  • Ability to strangle

REDUCING VALVES
Automatic valves that reduce the supply pressure to a preselected pressure. The supply pressure must remain at least as high as the selected pressure.

Advantage
  • Automatically reduce the supply pressure to the preset pressure

PINCH VALVES
The simplest of any valve design. Pinch valves consist of a molded sleeve of rubber or other synthetic material and a pinch mechanism. The pinch mechanism, a bar or gate, is lowered over the valve body to cut off the flow through the system.

Advantage
  • Relatively cheap
  • On / off, as well as regulation / regulation
  • Good for sludge, solid
  • Very suitable for difficult environments

BUTTERFLY VALVE
Rotary motion valves that can be used in on and off systems. They are fast and easy to operate. The flow control element is in a vertical or horizontal axis and opens when the handle is turned 90 degrees and closes when the valve rotates an additional 90 degrees.

Advantage
  • On / off as well as throttle / regular
  • Easy / fast operation
  • Good for large flow / low pressure applications due to weight / size / cost savings
  • Good for sludge / solids in suspension.


NEEDLE VALVES
Needle valves have a long, tapered, needle-like point, which is used to make relatively fine adjustments for flow. Sometimes they are used as components for other valves because the needle allows a gradual change in the size of the fluid flow opening.

Advantage
  • Good for a fine adjustment

RETENTION VALVES
Check valves are used in systems that employ gate valves because they prevent the flow reversal in the piping system and there is a low-pressure drop across the valve. The pressure of the fluid through the system opens the system, while the weight of the verification mechanism will close the valve if the flow is reversed.

Advantage
  • Avoid reverse flow