Self-acting temperature control valve is a new high-tech products without the help of external power or power, according to the initial setting automatically based on changes in the working temperature, continuous temperature control feedback, widely used in various types of thermal equipment of different nature of the mass temperature, flow control, such as metallurgy, chemical and various civil installations. Temperature-sensing element as a key component of the temperature control valve determines the performance of the temperature control valve.
The current self-operated temperature control valve has two kinds of temperature-sensing elements: one is the traditional paraffin temperature package (Wax Element), another new temperature control element using shape memory alloy (Shape Memory Alloys abbreviated as SMA) spring.
The traditional wax element works by pouring a mixture of wax and copper powder of different formulations into a small copper tube container, and the volume of the wax in the container increases or decreases due to the change of temperature, which is then adjusted by driving the spring to push the piston through the diaphragm at the mouth of the container.
A shape memory alloy spring made of Nitinol changes its length and force value by sensing temperature, thus pushing the spool to regulate and control temperature and flow.
As a new generation of thermal components, Nitinol memory springs have several distinct and disruptive advantages over traditional paraffin temperature packages.
1. The temperature-sensing action of the paraffin temperature pack has a significant hysteresis, according to the public article of the industry leader in paraffin temperature pack: "The response speed of the temperature pack to temperature in liquid is 15 to 20 seconds, while in comparison the temperature memory alloy spring in liquid can generally trigger a response in less than a second.
2. The natural aging and service life of the paraffin temperature pack is much shorter, usually only 3,000-5,000 times, due to the life limit of the rubber diaphragm and the delamination of paraffin and copper powder in it; while the service life of the memory alloy spring can easily reach 1 million times, or even tens of millions of times.
3. The action and force values in the temperature-sensing interval of the paraffin temperature package are nonlinear, which can easily cause temperature jumping changes and temperature control is not stable enough. Memory alloy spring temperature change is more controllable, more linear temperature response, temperature accuracy is more than 10-20 times the traditional paraffin temperature package, can be 0.1 ℃ of temperature change, do sensitive force response.
4. In accordance with the existing conventional materials and processing technology, the applicable temperature range of memory springs can cover -50 ℃ -150 ℃. If purely from the working range of Nitinol memory alloy, more can be expanded to -100 ℃ - 300 ℃, but then the memory spring test and adaptation conditions will present more challenges, while the applicable range of paraffin wax temperature package is only 5 ℃ - 90 ℃.
5. Compared to the characteristics of the paraffin wax ladle, which can only expand and contract thermally, the memory alloy spring can achieve not only the traditional thermal expansion and contraction, but also the "thermal expansion and contraction" through special materials and heat treatment process, and even the "dual-range memory state" of automatic reciprocating motion. ", providing more flexible options for customers' innovative design.
6. Paraffin wax temperature package uses copper material, the water is saline and alkaline, easy to corrode and produce a lot of scale; memory alloy spring composition is mainly nickel and titanium metal, with high corrosion resistance, not only can be used in hard water environment, even in seawater, sewage and acid and alkali corrosive environment can work normally.
7. Paraffin temperature package is only suitable for small stroke linear motion, while nickel and titanium temperature memory springs are not only made into compression springs and extension springs to make a larger stroke linear motion response to temperature changes; they can also be made into torsion springs, scroll springs, elastic diaphragms, shaped shrapnel and other forms to produce more diverse working responses such as torsion, flip and concave and convex.
8. Most of the temperature-sensitive actuators need to achieve accurate control response in relatively narrow temperature bands such as 10-15 ℃, when the paraffin temperature package for such small temperature changes in the implementation of the stroke, usually only 0.25-0.5 mm. Due to this huge difference in travel, the valve adjustment opening of the paraffin wax temperature pack actuator is relatively small, and the pipe pressure has to be increased significantly or the diameter of the valve itself has to be increased in order to obtain sufficient flow; while if the memory spring with 10 times larger travel is used, it can be used to achieve the same flow rate. memory spring, the pipeline pressure can be significantly reduced or the valve itself can be designed to be smaller, while achieving the same flow rate.
Due to the outstanding temperature control performance of nickel-titanium alloy memory springs, more and more temperature control spool manufacturers are no longer satisfied with the use of traditional paraffin temperature control elements, and began to start memory alloy springs as a new generation of temperature control elements to seek new technological breakthroughs and product upgrades.