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What factors should be considered when selecting external thread needle valves?
Date: 2025-12-08Read: 12
External thread needle valve is a common industrial control valve, belonging to precision regulating valves, widely used in industries such as chemical, petroleum, natural gas, power, and pharmaceuticals. Its main function is to precisely adjust the fluid channel through a needle valve core, thereby controlling flow rate, pressure, or liquid level. Needle valves usually have the characteristics of wide adjustable flow range, high adjustment accuracy, and good sealing. The external thread design facilitates their connection with pipelines, instruments, or other valves, making installation flexible and reliable.
External thread needle valveStructural characteristics:
1. Valve body
Valve bodies are generally made of stainless steel, carbon steel, or brass materials, which not only ensure pressure resistance but also have a certain degree of corrosion resistance. The internal channels of the valve body are precision machined to ensure smooth fluid flow and reduce flow resistance.
2. Valve core and needle tip
The valve core is needle shaped, with a conical or pointed front end, and flow regulation is achieved by rotating the valve stem up and down. The needle tip fits tightly with the valve seat to form a reliable seal. The high precision of valve core processing makes valve adjustment more precise, suitable for low flow or high-precision adjustment occasions.
3. Valve stem and handwheel
The valve stem is used to drive the movement of the valve core, and the handwheel rotates to drive the valve stem up or down. The valve stem is usually designed with a threaded fit to achieve slow and even adjustment. The handwheel can be selected as open-loop or locking type as needed to ensure safe operation.
4. Threaded interface
The external thread design complies with international or national standards, such as NPT (American taper thread) or G (British parallel thread), making it easy to directly connect pipe fittings or instruments. External threads not only facilitate installation, but also ensure a stable connection under high pressure.
5. Seals
To ensure no leakage, sealing materials such as polytetrafluoroethylene (PTFE), rubber, or metal gaskets are often used inside the valve. The selection of sealing components is closely related to the properties of the medium, temperature, and pressure.
Specific workflow:
When the valve is closed, the needle tip is tightly pressed against the valve seat, preventing fluid from passing through.
2. Operate the handwheel to drive the valve stem to rotate, gradually causing the needle tip to leave the valve seat and form a channel.
3. The size of the channel opening is determined by the height of the needle tip, and the larger the opening, the greater the flow rate; On the contrary, the traffic decreases.
When the valve is fully open, the flow resistance is minimized and a larger flow rate can be achieved; When in a semi open state, it is suitable for precise adjustment of flow rate.
When choosing an external thread needle valve, the following factors should be considered comprehensively:
1. Caliber and interface type
Select the valve diameter according to the pipeline specifications to ensure that the thread type matches the pipe fittings. Common specifications include 1/8, 1/4, 3/8, 1/2, etc.
2. Material selection
Select valve body and valve core materials based on the properties of the medium, temperature, and corrosiveness. Commonly used stainless steel materials are suitable for corrosive media, while brass materials are suitable for general industrial water or air.
3. Pressure level
The design pressure of needle valves should meet the system working pressure to avoid damage to the valve body or seals. Some high-pressure needle valves can withstand pressures of over 100MPa.
4. Sealing performance
The selection of sealing materials should take into account both medium compatibility and temperature range. PTFE seals are resistant to chemical corrosion but have limited resistance to high temperatures, while metal seals are resistant to high temperatures and pressures but require high precision in sealing surface processing.
5. Adjust accuracy and flow range
Select the valve needle tip shape, valve seat diameter, and valve stem stroke according to actual needs to meet precise control or fast switching requirements.