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我国阀门行业现状及发展趋势

2019-05-28  来自: 泰科菲阀门有限公司 浏览次数:113

我国已进入WTO,全球每年需求阀门约300万吨。要充分利用阀门业属劳动密集、劳动条件差、我国人均工资低廉,发达区域向发展中国生产转移等优势,积极走向世界经济的平台。分几个题目简述给排水阀门的现状与发展。

目前状况

现在约有3000家的大小阀门,其中温州600家,郑州近200多家,上海150多家,辽宁250家,江苏、福建各200余家,尽管良莠不齐,但产品品种已达3000多个型号,近3万个规格。在多品种、密封性能、强度要求、调节功能、动作性能和流通性能,特别是密封性能,都有了长足的进步,倒退十年前,城镇供水协会的权威人士有句行业名言说“十阀九漏”,虽然有些夸张,但确是事实。

造成阀门行业存在的众多问题主要是改革开放后,市场急速扩大,而原有国营阀门企业纷纷关停并转,本来机械工业水平就不高,于是乡镇企业(民营企业),雨后春笋般迅速发展起来,起点低,技术力量非常薄弱,设备简陋,产品大多数都是模仿生产,再加上市场混乱,特别是给排水用的低压阀门,问题严重。近十年来,在少数阀门企业的带动下,确有明显进步,桂隆泵阀总结有些品种甚至达到国际先进水平,还有许多企业进行二次创业。但就整体来说,差距还很大,有很多工作要做。为此,分别作出2010年、2020年技术进步、发展规划有着很重要的意义。

常用的阀门

在给排水工程中,中低压阀门的应用,特别低压大口径阀门(低压阀门是指公称压力PN≤1.6MPa的阀门),而中压阀门(PN2.5-6.4MPa)较少。而闸阀、蝶阀是基本应用的主导产品。

2.1闸阀的现状和发展

闸阀使用历史久,至今世界各国仍在应用,特别是DN300mm以下,在各类阀门中仍占主导地位。其特征是阀板前后压差使阀板强制压在出口右侧的阀座上,密封性较好,且全开时,由于阀板不留在流路上,压力损失小。用于切断管道中介质。

其缺点是操作力矩大,操作时易使阀体、阀杆损坏,特别是大口径闸阀。外形尺寸和重量也大,DN1000口径闸阀约3200mm高,需要四个人操作,所以闸阀一般使用在小口径,即DN500以下使用。

闸阀从全开到中间开度,阀门的流阻较小,接近全闭时,流阻急剧增加。较大的范围内,流阻变化较小,在接近全闭时,流量变化较大,不要在阀门接近关闭时使用,这时很难进行流量的微调。阀门若开度极小,开口处的流速极快,会使闸板下侧产生气蚀,并伴有激烈的振动和噪声,长时间节流运转,往往会使阀体和闸板的金属发生气蚀。闸阀工况若处在中间开度,阀板因为是靠两侧的导轨支撑,全闭时配合紧密,而中间位置时,阀板与导轨间隙大而产生振动。因此鸿丰认为,即使在气蚀发生率较低的区域,长时间使阀门节流运转,导轨也会发生畸形、磨耗或损坏,且由于阀座不是接触,而接触部位表面压力很高,往往会产生咬蚀或粘连,因此,不宜用于流量控制。还要注意,闸阀在小开度时,流量变化大,如果对阀门紧急启闭,会造成压力急剧上升或产生负压,特别是关阀门时水锤的产生。在金属密封闸阀基础上,近些年来开发了橡胶软密封闸阀,其特点是:

(1)法体底部无凹处,流体通过截面呈直线状,不易堆积和夹杂异物。

(2)闸板密封面是压在阀体上进行止水的,关阀力矩小。

(3)不因配管的弯曲和拉伸而影响密封性能。

(4)整个阀板衬橡胶,耐腐蚀,不出锈水。

(5)阀门可在全开通水的同时更换密封材料和O型圈。

(6)闸板互换性好。

由于功能优越,泰科菲看到国内外(特别在欧洲)需求量速增,软密封闸阀是30年前奥地利人发明,在欧洲每年生产50余万台,几乎100%使用,是硬密封闸阀的替代产品,其制造口径在欧日为DN500,美国一般用到DN400,而意大利可生产到DN1200。但也有不足,软密封闸阀是靠对橡胶阀座进行压缩密封的,是否关闭不好判断,要避免关阀过紧,不要超过关阀扭矩为好(扭矩在标准上给出)。

2.2蝶阀的现状和发展

泰科菲阀门记得上世纪三十年代,美国发明了蝶阀,上世纪七十年代传入我国,开发使用。目前世界上一般在DN300mm以上蝶阀已逐渐代替了闸阀。蝶阀与闸阀相比有开闭时间短,操作力矩小,安装空间小和重量轻等特点。以DN1000为例,蝶阀约2T,而闸阀约3.5T,且蝶阀易于各种驱动装置组合,有良好的耐久性和可靠性。

橡胶密封蝶阀缺点是作节流使用时,由于使用不当会产生气蚀,使橡胶座剥落、损伤等情况发生。为此,上世纪七十到八十年代国内外又开发金属密封蝶阀,耐气蚀、寿命长,近几年我国也开发了金属密封蝶阀,但要注意,阀体、阀座和阀板。阀座的材质不适组合时,阀座间会产生热咬合,又不能开闭的危险。在国外还开发耐气蚀、低振动、低噪声的梳齿形蝶阀。由于铸造技术的提高,可使铸铁的阀体、阀板与不锈钢阀座铸在一起,致使阀座部分的构造简单,导物不积留,耐久性、可靠性大大提高。一般密封座的寿命在正常情况下,橡胶15年以上,不锈钢金属约80年,综合比较各异。但如何正确选用则要根据工况要求。蝶阀的开度与流量之间的关系,基本上呈线性比例变化。如果阀门处于节流幅度较大状态,阀板的背面容易发生气蚀,有损坏阀门的可能,一般均在15度以外使用。节流侧阀门下面会产生负压,往往会出现橡胶密封件脱落。蝶阀操作力矩,因开度及阀门启闭方向不同其值各异,卧式蝶阀,特别是大口径阀,由于水深,阀轴上、下水头差所产生的力矩也不容忽视。另外,阀门进口侧装置弯头时,形成偏流,力矩会有增加。

2.3排气阀

旧式双孔排气阀由于排气能力小等原因,逐渐要被新型高速进排气阀代替。判定排气阀的性能高低除对阀门的一般要求外有三点至关重要:

(1)在大多压差下大孔口关闭。

(2)管道中介质——水,冲上来时是否会把浮球压住,孔口不能关闭。

(3)在低压时(0.02MPa)是否仍在密封不漏水。

排气阀口径的选择需要谨慎,特别管内产生负压时,需要补充,使管内负压不超过0.35kgf/cm2,否则管道会失稳破坏。

停泵水锤防护专用阀门问题

3.1水锤种类

水锤从不同角度,可分为四种。按关阀历时与水锤相μ的关系分为直接水锤和间接水锤;按水锤成因的外部条件可分为启动水水锤、关阀水锤和停泵水锤;按水锤水力特性可分为刚性水锤理论和弹性水锤理论两种;按水锤波动的现象分为水柱连续现象和水柱分离的水锤现象两种。

根据调查统计,在城市给水阀门和工业企业的给水泵站中,绝大部分水锤事故都属与停泵水锤事故。水锤事故危害性很大,会导致管道和设备的骤然炸破。由于本文只论及停泵水锤的防护,所以水锤的理论问题另做探讨。一般管道末端关阀水锤是先发生高压,后发生低压。泵站中停泵水锤的特点是先发生低压后发生高压,而且由于水泵电机旋转部分有的转动惯量,在停电后不是立即停止而是转速逐渐降低,仍处于水泵的工作状态,只不过扬程和水量都逐渐下降,当扬程降至与外部管道压力,流量变为0以后水开始倒流,此时水泵仍在正转受倒流水的作用,而转速很快下降,此阶段为制动阶段,进一步当水泵转速为0以后受倒流作用,推动水泵倒转,而开始进入水轮机工作状态,随后压力才逐渐升起。在整个低压(或负压)水锤波所延续的时间大于正常水锤波。低压(或负压)波时间,一般可由4、5秒到7、8秒。当水泵出口没有止回阀时,停泵后水可以通过水泵大量倒流泄水,使正压水锤压力,有效地减小,因此在的情况下可以去除水锤,防止水锤事故,但不能去除拉断水柱的水锤。当水泵出口装有止回阀时或水泵出口阀提早关闭,在水倒流后水能冲击止回阀迅速关闭,从而产生一个较大的关阀水锤,尤其当发生拉断水柱水锤时,回流水柱碰到关阀的止回阀上,将产生的水锤压力,这是我们主要的防护对象。停泵水锤防护专用阀门要适应这一过程的特点生产制造,而且在正常运行时水头损失要小,可靠。若管道假设为刚体,水锤压力式中

g——重力加速度m/s;

a——水锤波传播速度,近似1000m/s;

V——流速m/s;

L——管道长度m。

直接水锤多发生在管道较长,关阀速度较快时,所以关阀时间T的掌握非常重要,应满足

3.2阀门的气蚀问题

用气蚀系数δ值,来选定用作控制流量时,选择什么样的阀门结构型式中H1——阀后(出口)压力m;

H2——大气压与其温度相对应的饱和蒸气压力之差m;

ΔP——阀门前后的压差m;

其余符号同前。

各种阀门由于构造不同,因此,容许的气蚀系数δ也不同。如计算的气蚀系数大于容许气蚀系数,则说明可用,不会发生气蚀。如蝶阀容许气蚀系数为2.5,则:

如δ〉2.5,则不会发生气蚀。

当2.5〉δ〉1.5时,会发生轻微气蚀。

δ<1.5时,产生振动。

δ<0.5的情况继续使用时,则会损伤阀门和下游配管。

3.3阀门的卫生要求问题

自来水管道、阀门的卫生、防疫要求十分重要,目前仍没得到生产、施工、应用等各方面应有的重视,各种医药,食品现在加强了管理,但人们每天接触较多的水却很少有人问津,今后是我们应解决的一个重要问题。GB5749《生活饮用水卫生标准》和GB/T17219《生活饮用水输配水设备及防护材料的可靠性评价标准》要严格执行,必须有省级以上卫生防疫部门证明,浸泡试验规定的21个项目和其他3个项目,涂料应进行21个规定项目和5个其它项目的卫生要求应进行试验。原料达到食品级。

3.4阀门的防护问题

认为延长阀门寿命,保证阀门卫生要求,阀门金属表面必须作涂装,涂层厚度要保证,涂装工艺必须做好涂装前的金属表面处理,达到级(近白级),且推荐热喷涂。露天安装的阀门外表面宜再涂层外面涂耐紫外线的丙烯酸涂料。

不仅上述问题需要解决,还要优化流量系数,降低水头损失系数,并要研究提高大范围调压、调流(消能)的专用阀门生产技术,如:针阀(活塞阀)、多孔阀、环喷阀(固定锥阀)、隔水有保证的导流防止器等,及进一步开发超大型蝶阀(DN3000以上)等等。


    China has entered the WTO, global demand valve every year about 3 million tons. We should make full use of the advantages of the valve industry, such as labor intensity, poor labor conditions, low per capita wages in China, and the transfer of production from developed countries to developing countries, so as to actively go to the platform of the world economy. The present situation and development of water supply and drainage valves are described in several titles.

Current status

Now there are about 3000 size valves, including 600 in wenzhou, nearly 200 in zhengzhou, more than 150 in Shanghai, 250 in liaoning province, and more than 200 in jiangsu and fujian provinces. In many varieties, seal performance, strength requirements, adjustment function, movement performance and circulation performance, especially seal performance, have made great progress. Ten years ago, the authority of urban water supply association had a famous industry saying that "ten valves and nine leaks", which was exaggerated but true.

Cause many problems of the valve industry mainly after the reform and opening up, market expand rapidly, and the original state-owned enterprises valve were shut down and go, original mechanical industry level is not high, so the township and village enterprises (private enterprises), have developed rapidly, low starting point, technical force is very weak, poorly equipped, most products are imitation production, plus market chaos, especially water supply and drainage with low pressure valves, serious problems. In the past decade, under the guidance of a few valve enterprises, there has been significant progress. Guilong pump valve summarizes some varieties and even reaches the international advanced level. But overall, the gap is wide and there is a lot of work to do. Therefore, it is of great significance to make technological progress and development plans for 2010 and 2020 respectively.

Service valve

In water supply and drainage engineering, medium and low pressure valves are widely used, especially low-pressure large-diameter valves (low-pressure valves refer to those valves whose nominal pressure PN is less than 1.6mpa), while medium-pressure valves (pn2.5-6.4mpa) are less. Gate and butterfly valves are the most basic and widely used leading products.

2.1 status and development of gate valves

Gate valves have been used for the longest time, and they are still used in the world today, especially under DN300mm. Its characteristic is the valve plate front and back pressure difference makes the valve plate presses firmly on the seat on the right side of the outlet, sealing is better, and when fully open, because the valve plate does not stay on the flow path, the pressure loss is small. Used to cut off medium in pipe.

The disadvantages are high operating torque and easy to damage valve body and stem during operation, especially large caliber gate valve. The contour size and weight are also large. The DN1000 caliber gate valve is about 3200mm high and needs to be operated by four people. Therefore, the gate valve is generally used in small diameter, that is, it is used below DN500.

Gate valve from full open to middle open, the valve flow resistance is small, close to full closed, flow resistance increased sharply. In a larger range, the flow resistance changes less. When the valve is close to full close, the flow rate changes more. Do not use it when the valve is close to closing. If the valve is extremely open and the flow rate of the opening is extremely fast, cavitation will occur on the lower side of the gate, accompanied by intense vibration and noise. Prolonged throttling operation will often cause cavitation to the metal of valve body and gate. If the gate valve operates at the middle opening, the valve plate is supported by the guide rails on both sides. When it is fully closed, it is closely matched, and when it is in the middle position, the gap between the valve plate and the guide rail is large, resulting in vibration. Therefore, hongfeng believed that even in the area with a low incidence of cavitation, the valve will be throttled for a long time and the guide rail will be misshapen, abrasion or damage, and because the seat is not in full contact and the surface pressure on the contact site is high, there will often be bite or adhesion, so it should not be used for flow control. It should also be noted that the flow rate of the gate valve changes greatly when it is opened in a small degree. If the valve is opened and closed urgently, the pressure will rise sharply or produce negative pressure, especially the water hammer when the valve is closed. Based on metal seal gate valves, soft rubber seal gate valves have been developed in recent years.

(1) there is no depression at the bottom of the body, and the fluid passes through the section in a straight line, which is not easy to accumulate and foreign body.

(2) the sealing cover of gate plate is pressed into the valve body for stopping water, and the closing moment is small.

(3) the sealing performance is not affected by pipe bending and stretching.

(4) the entire valve plate is lined with rubber, resistant to corrosion and free of rust.

(5) the valve can change sealing material and o-ring at the same time of full open water supply.

(6) good interchangeability of gate.

Because of superior function, hong feng see the world, especially in Europe, demand surge, Austrian invention soft-sealing gate valve is 30 years ago, annual production of more than 50, ten thousand units in Europe, with almost 100% use, is a hard seal gate valves replacement products, its manufacturing caliber in the day to DN500, America generally use DN400, to 48 ") may be produced in Italy. However, there are also deficiencies. The soft sealing gate valve relies on the compression seal of the rubber seat. It is not good to judge whether it is closed.

2.2 status and development of butterfly valves

Guelong valve remember the 1930s, the United States invented the butterfly valve, the 1970s introduced into China, development and use. Currently, butterfly valves generally over DN300mm have gradually replaced gate valves in the world. Compared with gate valve, butterfly valve has the characteristics of short opening and closing time, small operating torque, small mounting space and light weight. In the case of DN1000, butterfly valve is about 2T while gate valve is about 3.5t. Moreover, butterfly valve is easy to be combined with various driving devices and has good durability and reliability.

The disadvantage of rubber sealing butterfly valve is that when it is used for throttling, air corrosion will be produced due to improper use, which will result in spalling and damage of rubber seat. Therefore, in the 1970s and 1980s, metal sealing butterfly valve was developed internationally, which is resistant to gas corrosion and has a long life. In recent years, metal sealing butterfly valve has been developed in China, but attention should be paid to valve body, seat and valve plate. When the seat material is not combined, there is a risk of hot bite between the seats, which cannot be opened or closed. Also developed in the foreign air corrosion, low vibration, low noise comb - tooth butterfly valve. Due to the improvement of casting technology, cast iron valve body, valve plate and stainless steel seat can be cast together, resulting in the simple structure of the seat part, lead does not accumulate, durability, reliability greatly improved. Under normal circumstances, the life of general seal seat, rubber more than 15 years, stainless steel metal about 80 years, comprehensive more different. But how to choose correctly depends on the working condition. The relation between the opening of butterfly valve and flow rate basically shows linear proportional change. If the valve is in a state of greater throttling, the backside of the valve plate is prone to cavitation, which may damage the valve and is generally used beyond 15 degrees. Negative pressure will be generated under the throttling side valve, and rubber seals will often come off. The operating torque of butterfly valve is different due to different opening degree and valve opening and closing direction. Horizontal butterfly valve, especially large diameter valve, also cannot be ignored due to water depth. In addition, when the elbow of valve inlet side device forms a bias current, the torque will be increased.

2.3 exhaust valve

Due to small exhaust capacity and other reasons, the old double-hole exhaust valve is gradually replaced by a new high-speed intake and exhaust valve. In addition to the general requirements for the valve, it is of great importance to determine the performance of the exhaust valve:

(1) the large orifice is closed under most pressure differences.

(2) whether the medium in the pipe -- water will press the floating ball when rushing up, and the orifice cannot be closed.

(3) at low pressure (0.02MPa) whether the seal is still watertight.

Careful selection of exhaust valve caliber should be made. When negative pressure is generated in the pipe, it should be replenished so that the negative pressure in the pipe does not exceed 0.35 KGF /cm2. Otherwise, the pipe will be destabilized and damaged.

Stop pump water hammer protection special valve problem

3.1 types of water hammer

Water hammer can be divided into four types from different angles. According to the relationship between the valve closing time and the water hammer, it can be divided into direct water hammer and indirect water hammer. According to the cause of formation of water hammer, the external conditions can be divided into starting water hammer, closing valve water hammer and stopping pump water hammer. According to the hydraulic characteristics of water hammer, it can be divided into two kinds: rigid water hammer theory and elastic water hammer theory. According to the fluctuation of water hammer, there are two kinds of water hammer phenomena: water column continuous phenomenon and water column separated water hammer phenomenon.

According to the survey statistics, in the urban water supply valve and the pump station of industrial enterprises, most of the water hammer accidents belong to the stopping pump hammer accidents. Water hammer accidents can be dangerous, causing sudden explosions of pipes and equipment. The paper only deals with the protection of water hammer, so the theory of water hammer is discussed. The common pipe end shutoff valve water hammer is the first high pressure, then low pressure. Stop pump water hammer in pumping station is the characteristics of high pressure in the aftermath of the low pressure, and as the water pump motor moment of inertia of rotating parts have, instead of immediately stop after a power outage speed gradually reduced, is still in the water pump working condition, only the head and water were gradually decline, when the head fell to with external pipeline pressure, flow becomes zero after the water began to flow back, when the pump is still in turn is back in the water, and the speed decreases quickly, at this stage for the braking phase, further when the pump speed to 0 after the flow back, pushing back water pump, and began to enter the turbine working state, then the pressure rises gradually. The duration of water hammer wave at the whole low pressure (or negative pressure) is greater than that of normal water hammer wave. Low pressure (or negative pressure) wave time, generally from 4, 5 seconds to 7, 8 seconds. When there is no check valve at the outlet of the pump, the water after stopping the pump can discharge water by a large number of backflow through the pump, so that the pressure of positive pressure water hammer can be effectively reduced. Therefore, the water hammer can be eliminated under certain circumstances to prevent water hammer accidents, but the water hammer that pulls the water column cannot be eliminated. When export pump equipped with check valve or pump outlet valve closed early, after the water flow back water impact quickly close check valve, so as to produce a large valve water hammer, especially when the tensile spout water hammer occurs, reflux met shut valve, check valve on the water column will have a huge water hammer pressure, this is our main object of protection. The special valve for stopping the pump water hammer protection should adapt to the characteristics of this process, and the loss of head should be small in normal operation, safe and reliable. If the pipe is assumed to be rigid, water hammer pressure

G -- gravity acceleration m/s;

A -- water hammer wave propagation speed, approximately 1000m/s;

V -- velocity m/s;

L -- pipe length m.

The direct water hammer often occurs when the pipe is long and the closing speed is fast, so the control of the closing time T is very important and should be satisfied

3.2 cavitation problem of valve

What type of valve structure H1 -- post-valve (outlet) pressure m is selected as the threshold value of cavitation coefficient to control the flow rate;

H2 -- difference of saturated vapor pressure between atmospheric pressure and temperature m;

Δ P - before and after the valve differential pressure m;

The rest of the signs are the same.

Valves are constructed differently, so the allowable cavitation coefficients vary. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, it indicates that cavitation can be used and will not occur. If the allowable cavitation coefficient of the butterfly valve is 2.5, then:

Cavitation will not occur if raw material is 2.5.5.

Slight cavitation will occur when 2.5 > is inserted into > 1.5.

When is less than 1.5, vibration is generated.

Valve and downstream piping may be damaged if continued in conditions<0.5.

3.3 sanitary requirements of valve

The sanitation and epidemic prevention requirements of water pipes and valves are very important, which have not received due attention in production, construction and application at present. The management of various medicines and food has been strengthened. However, the water that people are exposed to most every day is rarely received. GB5749 "drinking water health standards" and GB/T17219 ShuPeiShui life drinking water equipment and protective materials safety evaluation standards should strictly carry out, must have a health and anti-epidemic departments at or above the provincial level certificate, immersion test regulations of 21 and other three projects, coating should be 21 and five other projects of health requirements should be tested. Raw materials reach the food grade.

3.4 valve protection

It is believed that to extend the service life of the valve and ensure the sanitary requirements of the valve, the metal surface of the valve must be painted, the coating thickness should be guaranteed, and the coating process must be well done before coating, reaching the level (near white level), and hot spraying is recommended. Outdoor installation of the valve surface should be re - coated with uv - resistant acrylic paint.

Not only needs to solve the above problem, but also to optimize the flow coefficient and lower head loss coefficient, to study and improve the wide range of voltage regulation, basins (energy dissipation) special valve manufacturing technology, such as: porous valve, needle valve, piston valve, ring preventer (fixed cone valve), water guaranteed diversion preventive device, etc., and the further development of very large butterfly valve (DN3000 above), and so on.

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