Tips for selection of the hottest high temperature

2022-08-03
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Tips for selection of high temperature control valve

high temperature regulation and control is a difficult problem in automatic control implementation, and it is more difficult to cut off high temperature and ultra-high temperature. The main performance of this problem is that the high-temperature expansion causes blocking and cutting off. Therefore, high temperature and ultra-high temperature control has always been the focus of domestic and foreign manufacturers and design institutes

I. several problems that should be paid attention to

from the perspective of design, type selection and use, the following problems should be paid attention to:

(1) the selection of valve body and valve trim materials

for regulating valves used in environments above 450 ℃, the influence of temperature and pressure conditions on the mechanical strength of materials must be considered in the design and selection, such as under the high temperature conditions of boiler feed water system and superheated bypass system, Conventional valve body and trim materials are not applicable (such as O-ring, tetrafluoro material, elastic material, standard gasket, etc.). Therefore, more durable materials must be selected. The maximum temperature for general materials is about 500 ℃. For occasions higher than 538 ℃, the valve body is usually made of chromium molybdenum steel with the help of the fixing clip. SUS310S stainless steel is usually selected for the occasions where the maximum 5 safety devices and limit devices should be sensitive and reliable, and the temperature reaches about 1035 ℃, and the carbon content of the material must be controlled between 0.04 ~ 0.08%. For higher temperatures, it is recommended to use lining non-metallic heat-resistant materials (which can be used for high temperature occasions of 1200 ℃) or special high-temperature high-strength alloys (such as high-temperature high-strength alloys for engine combustion chambers, which can be directly used for high temperature occasions of 1000 ℃)

(2) influence of thermal expansion and cold contraction

the structure and valve internals of high-temperature valve and normal temperature valve are very different, such as guide clearance, valve plate rotation clearance, bearing mode, etc. In addition to design and manufacturing control, it is preferable to reduce the influence of thermal expansion and cold shrinkage from the selection of valve type structure. Practice has proved that the flapper butterfly valve is a very good high-temperature valve. The gap between the flapper and the inner cavity of the valve body is 3 ~ 6 mm, which can completely solve the problem of high-temperature jamming between the valve plate and the inner cavity of the valve body, and achieve high cutting performance (5 ×)。

the common positioning and guiding structure is not reliable when the medium temperature is higher than 400 ℃. At this time, the external bearing structure shall be used to ensure the positioning and support of the valve plate, so as to avoid the impact of internal high temperature on the guide structure. The "Japanese" patented positioning system invented by Hualin company can play a very good role in positioning, supporting and protecting, ensure the accurate positioning of the valve plate in the longitudinal direction, and avoid the blockage caused by the drooping of the valve plate due to gravity. At the same time, because the positioning system bears the gravity of the valve plate and valve rod, it reduces the load of the actuator and the load of the external bearing, avoids the unilateral jamming phenomenon that is easy to occur when the conventional butterfly valve is installed horizontally, and can be installed vertically

(4 "this is the first time that carbon fiber is widely used in mass production vehicles) temperature resistance of packing

standard PTFE packing can only be used in occasions below 200 ℃. If it is used in medium and high temperature occasions, an extended bonnet must be used to prevent the packing from being affected by extremely high temperature. However, the longer and thinner valve rod has poor strength under high temperature conditions and is prone to bending. Therefore, it should have excellent temperature resistance under high temperature conditions (up to 600 ℃) flexible graphite packing can also greatly reduce the height of the extended bonnet. At the same time, the method of "rotary valve + coarse valve stem" is used to improve the overall strength of the valve, so as to better solve this problem

(5) selection of sealing methods

it is difficult to achieve high cutting performance under high temperature conditions, and many conventional high-performance sealing methods are not desirable (such as O-rings, tetrafluoro materials, elastic metal materials, etc.). Under 500 ℃, special composite graphite valve seat soft sealing method can be adopted. Typical products include Hualin's soft seal high-temperature O-type cut-off ball valve, V-type ball valve and soft seal high-temperature full-function ultra light regulating valve. When the temperature is above 500 ℃, only metal to metal hard sealing method can be adopted (butterfly valve structure is generally adopted). In order to prevent the blockage caused by material expansion at high temperature, the sealing clearance is usually large. As a result, the leakage rate is high. In order to solve this problem, Hualin company has developed a high-temperature flapper butterfly valve, which adopts the process that the plane baffle (valve plate) falls on the valve body boss (integrated), forming a circular sealing surface, achieving good sealing effect, and the leakage rate is only ~. At the same time, the wear-resistant alloy overlaid on the sealing surface makes the valve have better sealing reliability and longer service life

II. Typical high temperature control valve

(1) ordinary high temperature alloy butterfly valve

ordinary butterfly valve is a butterfly valve with simple structure and the lightest weight of the same caliber. It is easy to forge and shape, which can save a lot of valuable high temperature alloy. Ordinary high-temperature alloy butterfly valve can only be used in occasions with low leakage requirements. In the application, it should also be noted that there should be enough clearance between the valve body and the valve plate to avoid jamming caused by material thermal expansion under high temperature conditions. At the same time, appropriate positioning measures (such as Hualin "sun" type positioning system) shall be taken to ensure the effective positioning of the valve plate, so as to avoid the valve plate sagging and shifting, resulting in unilateral jamming or seizure

(2) high temperature alloy flapper butterfly valve

flapper butterfly valve is a new type of high temperature control valve developed to solve the main problems that control valve is prone to occur under high temperature conditions. Opal filled in polyethylene has obvious rigidity and toughness modification. It has the advantages of simple structure, easy forging, good sealing and not easy to jam. It can also save a lot of valuable high temperature resistant alloys. The sealing method is that the plane baffle (valve plate) falls on the valve body boss (integrated), forming a circular sealing surface, so as to achieve a good sealing effect. There is no gap fit between the valve body and the valve plate of this product. If the Hualin "sun" type positioning system is used at the same time, the valve plate position can be more effectively guaranteed, the load of the actuator can be reduced, and the phenomenon of unilateral jamming or seizure can be avoided

(3) special ball valve for high temperature heat transfer oil

the special ball valve for high temperature heat transfer oil with elastic laminated special composite graphite valve seat and flexible graphite packing can effectively meet the requirements of good cut-off and adjustment of heat transfer oil process, small influence of heat transfer oil on the packing (conventional elongated bonnet and heat sink are meaningless), and good sealing. It is a medium and high temperature cut-off control valve with excellent performance, which can be applied to occasions below 500 ℃

(4) the ultra-high temperature butterfly valve with high temperature resistant non-metallic inner sandwich

uses ultra-high temperature resistant alloy material as the structure and high temperature resistant non-metallic material as the lining, so as to distinguish the inside and outside of the valve body, thus ensuring the strength of the valve body. Hollow or ultra-high temperature resistant alloy valve plate with circulation or cooling means can ensure that the valve plate works well at about 1200 ℃. At the same time, the "Japanese" type positioning system with Hualin patented technology can more effectively ensure the positioning of the valve plate, reduce the load of the actuator, and avoid jamming, seizing and damage to the lining non-metallic materials

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