Needle valves are a subset of control valves designed specifically for that purpose. Their precision and repeatability make them ideal for controlling fluid flow in small systems like instrumentation or fuel regulation.
There are primarily two needle valve body types on the market. Please refer to the post below for more discussion on needle valves.
Uses Of A Needle Valve
Due to their versatility and precision, needle valves can be used in various fluid control applications. Depending on the material and size of the valve, it can be utilized with a wide variety of clean gases and fluids within a narrow temperature and pressure range.
Needle valves are frequently used to control the flow of gases like propane throughout a system. A propane needle valve can be used to precisely cut off the gas supply and/or regulate the flow rate, allowing the burner’s efficiency to be monitored.
All of the following make considerable use of needle valves:
- Needle valves regulate the pressure and flow of water in dams, reservoirs, power plants, and water distribution networks.
- In automated combustion control systems, needle valves are used to manage fuel flow.
- You can use these valves to turn off a pressure gauge or regulate the flow rate in a flow meter.
- By regulating the amount of air going into the cylinders, needle valves can adjust how quickly the pistons move.
Engineering Of Needle Valves
The three main components of a needle valve assembly are the valve body and seat, the stem along with the stem tip, and the packing and bonnet. Needle valves are often made with hex or square bar stock for their bodies due to their small size. Z-shaped flow channels across the body are common, as are L-shaped flow paths, often known as globe patterns or angle patterns.
Normally, the needle’s position in relation to the seat can be adjusted with the help of fine threads on the stem, much like a micrometer. It is common practice to prevent the valve settings from being altered by vibration by providing a locking mechanism, either internally or on the stem, with a set screw, locknut, etc.
Scales are sometimes incorporated to allow for precise resetting of the flow rate. It is common practice for manufacturers to offer graphs depicting the linear relationship between stem rotation and flow coefficient, Cv.
The packing in the crown ensures that the stem can rotate without leaking. Common packing materials include O-rings, PTFE; often used for ptfe seals, and graphite. A gland nut or packing nut regulates the pressure inside a sealed system.
Two-piece stems are sometimes used to seal off the stem threads from the media and prevent any thread lubricant from seeping into the process fluids. The valve bonnet may be molded together with the rest of the valve body, or it may be a separate piece that is threaded into the valve and secured by a nut.
When the valve is fully open, the stem seals against a rear seat, preventing any fugitive emissions. In the case of needle valve vs ball valve, the stem is secured in some way that makes removal by backing impossible.
Choice of Needle Valves
There are four primary factors to consider when picking a needle valve: the material, the pressure, the size, and the temperature.
The material of the needle valve housing is application-dependent. Due to their wide chemical resistance, brass and stainless steel are the most popular materials for valve housings. However, additional materials are available for more specialized uses.
Needle valves made of brass are used in various settings, including gas pipes, hydraulics, and potable water distribution. They function well in non-aggressive environments and are widely used in potable water systems. The usage of seawater, distilled water, acids, or chlorides renders them useless.
Needless to say, stainless steel needle valves are highly resistant to practically any chemical medium. Despite being subjected to intense heat and pressure, the material remains sturdy and reliable. It can withstand abrasive and corrosive conditions such as seawater, yet prolonged exposure will induce corrosion.
Needle valves made of plastic are used to precisely regulate non-corrosive and pure fluids. Plastic melts at temperatures above 60 degrees Celsius and bursts under pressure. That’s why delicate industries like medical molding firms follow special protocols to produce the best plastic equipment.
- Sizing Of Openings, Ports, And Orifices
Port and orifice diameters for needle valves come in a wide variety. One or both ends of the connection ports can be configured to be male or female. National Pipe Thread (NPT), British Pipe Thread (BSP), and metric are common thread specifications (ISO standards).
The standard size for needle valves is between 2 and 12 mm (about 1/8″ and 2″). Correct port and orifice sizing promote smooth flow and reliable system operation by minimizing wear and leakage.
Needle valves can be used in environments with temperatures both high and low. Make sure the valve housing and packing/sealing material can resist the conditions by giving precise specifications, especially at high temperatures.
Both PTFE (Teflon) and PEEK (Polyether Ether Ketone) is widely used as sealing materials due to their high heat resistance; PTFE can withstand temperatures between -65 degrees Fahrenheit (-54 degrees Celsius) and 450 degrees Fahrenheit (315 degrees Celsius), while PEEK can withstand temperatures up to 600 degrees Fahrenheit (315 degrees Celsius).
Advantages Of Needle Valves
- Precise flow regulation, especially in low-flow situations
- Miniature in stature
Disadvantages Of Needle Valves
- High-pressure drop due to severe fluid flow impediment.
- The needle and seat could be damaged if the fluid has suspended particulates.
- Looking at the needle valve handle tells you nothing about the valve’s open or closed status.
In this post, we quickly looked at the basics of needle valves, covering topics like how they’re made, where they might be used, and how to pick the right one. We hope you found the guide useful.
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