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What is a valve?
A valve can be defined as a mechanical element with which the circulation of liquids or gases can be started, stopped or regulated by means of moving parts that open or close, partially or totally, the passage of the fluid. Valves must be understood within the context of an installation with pipes, union accessories and pumps.
There are multiple types of valves that depend on the type of closure system: ball valve, gate valve, butterfly valve, guillotine valve, needle valve, among others.
Needle valves are used mostly in instrumentation and are called this way because of the type of closure system they have; It is a stem that ends in a thin point similar to a needle and that closes and/or opens a passage fitting into a small hole inside its body.
Manifold
This device (composed of several elements) is widely used in industries due to its function and the facilities it provides in production lines.
A manifold consists of a set of cylinders and valves that manage the fluids or gases that are supplied in a certain sector of a production line or plant. The device manages to control gases or liquids by closing and opening (as the case may be) simultaneously, this allows the products to be suspended or allowed to continue their trajectory.
It can be differentiated from a needle valve basically because the needle valve has a flow inlet and an outlet, although there are some with two outlets that could be considered manifolds. The manifold, on the other hand, has one or more flow inlets and two or more outlets.
Lately, compact manifolds have been manufactured that closely resemble needle valves, hence the confusion between the two devices.
Why use needle valves and manifolds
Having explained what needle valves and manifolds are, it is almost evident that they are quite useful tools in the industry, which must be made with the necessary quality to prevent, when managing the flow of different materials, those that should not coincide from mixing or that said flow is blocked, as well as preventing leaks. Below are some of the uses and benefits of these instruments:
- Allows you to protect equipment from being subjected to excessive pressure or high temperatures.
- Reduces leak risks by minimizing connections.
- Decreases the distance the material must travel.
- If they are centralized, it is possible to execute several operations in the same space and at the same time.
- Isolates pressure.
- It makes it easier to reduce maintenance and installation costs.
- Enables a safe way to calibrate, lock or isolate instruments.
- Allows you to rectify, redesign or take advantage of limited spaces.
Types of needle valves and manifolds
The type of needle valve depends on the nominal pressure, closing seat, size and utility. In that order of ideas there are several types of needle valves:
- Mini or compact valve.
- Soft seat valves.
- Hard seat valves.
- Medium pressure valves.
- High pressure valves.
- Standard valves without purge.
- Valves with purge.
- Block and bleed valves.
- Double block and bleed valves.
Likewise, the manifold types for instrumentation also depend on the same variables. The most standard according to their usefulness and application are:
- Static pressure lockout and bleed, hard and soft seat.
- Fluid level, hard and soft seat.
From these it depends on the number of outlets and purges they have. There are two, three, four and five outlets with one or double purge.
How to select the right valves
The selection of a valve or manifold is very important in the proper design and maintenance practice of industrial, piping and instrumentation systems. Without the right valve for a specific application, operators could face inadequate or poor fluid system performance, increased downtime, and avoidable safety risks.
For the correct selection of valves or manifolds, the STAMPED method can be followed. This takes into account: size, temperature, application, fluid, pressure, ends or fittings of the final connections and delivery. (All this according to its acronym in English, size, temperature, application, media, pressure, ends and delivery).
Size:
The size of your valve or manifold determines its flow capacity and should correspond to the desired (or required) flow rate of your system.
Manufacturers will provide a flow coefficient (Cv), which indicates the relationship between the pressure drop across the valve and the corresponding flow rate.
Temperature:
The temperatures at which your valve or manifold will operate must be taken into account, both the temperature of the system fluid and the working temperature of the environment. It is important to take into account fluctuations or changes in these temperatures. These conditions may influence valve or manifold selection or how often you will need to perform preventative maintenance.
Temperature fluctuations can cause closure materials to expand and contract. Likewise, metal components can lose strength at higher temperatures, reducing pressure ratings.
Application:
Consider what your valve or manifold needs to do in your system. Do you need to open or close the flow? Regulate the flow level? Control flow direction? Protect the system from excess pressure? The answers to these questions will define the type of valve or manifold you will select for your design, for example, if your intention is to reduce or regulate flow, a needle or regulating valve may be the best option.
Fluid:
The process fluid must also be carefully analyzed while seeking to select the correct valve or manifold with the proper material composition. You must ensure that your system fluid is compatible with the materials of construction of the valve bodies, seats, plugs and other softer materials. Incompatibility can lead to corrosion, brittleness or stress corrosion cracking problems; All of which can pose safety risks as well as expensive production problems.
Pressure:
Pressure is another important consideration in your valve or manifold selection. There are two pressures to take into account:
- Operating Pressure: The normal operating pressure of your system.
- Design pressure: The maximum pressure limit is provided by the valve manufacturer; Never exceed the design pressure of any fluid system component except under controlled test conditions.
The pressure limitation of a fluid system is based on its lowest-ranking component (remember this when selecting your valve).
The pressure and temperature of the process fluid have a considerable impact on component performance. The valve you select must maintain pressure and operate when necessary and under a wide range of temperatures and pressures.
Final connections:
Valves are designed with a variety of different end connections. These can be integral tube fittings, threads, pipe flanges, welded ends, etc. For instrumentation, connections are generally threaded in sizes of ¼” male or female NPT threads. Although not traditionally associated with valve construction, the selection of end connections is critical to the overall composition of the valve and its ability to maintain a watertight system. Ensure that the end connections are appropriate for the pressure and temperature of your system and are the correct size. The correct end connection can simplify installation and prevent additional leak points.
Delivery:
No less important is your supplier’s delivery time. Once you have considered each of these factors and selected the most appropriate valve for your application, the next question is: “When do I need them? How many do I need?” On-time delivery and reliable supply are as important to keeping your fluid system operational and efficient as any other factor.
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