Needle valve
A needle valve is a type of valve with a small opening and a threaded, needle-shaped valve piston . It enables precise regulation of the flow.
Structure and functionality
The valve piston can be moved lengthways through the thread . The needle-shaped tip only slightly enlarges or reduces the opening of the valve, since the needle has to be moved relatively far for even small changes. The small cone angle of the needle enables a very sensitive setting of the flow rate.
Packing-sealed valves are dynamically sealed valves. Dynamic seal means that a relative movement between the sealing body (stem / ball / chick ) and the sealing material is possible. The latter is also called a pack.
Typical sealing materials are Teflon or O-rings made of Perbunan , Viton , EPR / EPDM , Kalrez for standard valves , PEEK or graphite for valves for higher temperatures. These valve types have silicone-based lubrication ex works . This increases the service life of the packing, minimizes wear in the valve and reduces the required actuation torque.
Needle valves with stem packing above the stem thread
- Possible unwanted effects
- Contamination of the media by lubricants and particles from the spindle thread
- Washing of the lubricants from the thread, stiffness up to seizure of the spindle thread.
- Incompatibility of the media with the lubricants
- Measurement errors in the chromatography due to undesired media contamination
- Often defective valve seats due to improper handling (with metal seat)
- Bad to clean z. B. with crystallizing media or after adding solids.
- advantages
- Relatively inexpensive valve for simple applications, robust when used correctly
- Available with different spindle tips: locking, regulating, soft seat, non-rotating spindle tip
- Pack adjustable from the outside
Needle valves with stem packing below the stem thread
- Possible unwanted effects
- Often defective valve seats due to improper handling (with metal seat)
- Relatively high actuation torque as it is designed for high pressures
- Bad to clean z. B. with crystallizing media or after adding solids
- advantages
- Robust valve with a non-rotating spindle tip, which means that seat damage or scoring on the tip is less common
- Available with different spindle tips: stainless steel, soft seats such as PCTFE or PEEK, Stellite (hard alloy based on cobalt - chrome ), as well as shut-off, regulating tip or ball (for rough applications)
- with graphite packings for temperatures up to max. 649 ° C suitable
- Due to the position of the packing, the medium is not contaminated or the lubricant is washed out of the thread
- externally adjustable packing
Typical applications
- Laboratories
- Industrial gases
- Plant and process engineering
- Research and Development
- Armaments, aerospace
- general gas units up to max. 5.0.