低溫閥是一種在低溫介質(zhì)中工作的閥門(mén)。隨著現(xiàn)代科技的發(fā)展，低溫工程制品的生產(chǎn)規(guī)模不斷擴(kuò)大，液氧、液氮以及液化石油氣等得到廣泛的應(yīng)用。尤其是液化天然氣越來(lái)越受到世界各國(guó)的重視。液化氨的溫度-269℃，液氫的溫度-254 ℃，液化氦的溫度-196 ℃，液氧的溫度-183 ℃，液化天然氣的溫度-162 ℃，以上物質(zhì)的液化分餾，運(yùn)輸和儲(chǔ)存都需要使用大量的低溫閥門(mén)。低溫閥門(mén)的用途越來(lái)越廣，需求越來(lái)越大，對(duì)低溫閥的技術(shù)性能和工作特性的要求也在不斷提高。

　　Low temperature valve is a type of valve that operates in low-temperature media. With the development of modern technology, the production scale of low-temperature engineering products continues to expand, and liquid oxygen, liquid nitrogen, and liquefied petroleum gas are widely used. Especially liquefied natural gas is receiving increasing attention from countries around the world. The temperature of liquefied ammonia is -269 ℃, the temperature of liquid hydrogen is -254 ℃, the temperature of liquefied helium is -196 ℃, the temperature of liquid oxygen is -183 ℃, and the temperature of liquefied natural gas is -162 ℃. A large number of low-temperature valves are required for the liquefaction, distillation, transportation, and storage of these substances. The application of low-temperature valves is becoming more and more extensive, and the demand is increasing. The requirements for the technical performance and working characteristics of low-temperature valves are also constantly improving.

　　低溫閥門(mén)主要有閘閥、截止閥、球閥、蝶閥、止回閥等，其主要結(jié)構(gòu)與常用大致相同；但其有自身的特殊性

　　Low temperature valves mainly include gate valves, globe valves, ball valves, butterfly valves, check valves, etc., and their main structures are roughly the same as commonly used ones; But it has its own particularity

　　低溫閥的溫度等級(jí)：國(guó)外根據(jù)各種不同氣體在常壓下的液化溫度一般分為六種溫度級(jí)。一級(jí)二級(jí)三級(jí)四級(jí)五級(jí)六級(jí)0~-46℃-47~-60℃-61~-70 ℃-70~-101 ℃-102~-196℃-253 ℃以下

　　The temperature level of low-temperature valves: In foreign countries, there are generally six temperature levels based on the liquefaction temperature of various gases under normal pressure. Level 1, Level 2, Level 3, Level 4, Level 5, Level 6: 0~-46 ℃ -47~-60 ℃ -61~-70 ℃ -70~-101 ℃ -102~-196 ℃ -253 ℃ or below

　　一.低溫閥門(mén)的特殊結(jié)構(gòu)

　　One Special structure of low-temperature valve

　　1.閥體?閥體應(yīng)能充分承受溫度變化而引起的膨脹、收縮，且閥座部位的結(jié)構(gòu)不會(huì)因溫度變化而產(chǎn)生永久變形。

　　1. Valve body? The valve body should be able to fully withstand the expansion and contraction caused by temperature changes, and the structure of the valve seat should not undergo permanent deformation due to temperature changes.

　　2.閥蓋：采用長(zhǎng)頸閥蓋結(jié)構(gòu)，其目的在于能起保護(hù)填料函的功能，因?yàn)樘盍虾拿芊庑允堑蜏亻y的關(guān)鍵之一，該處有泄漏點(diǎn)。這是因?yàn)樵诘蜏貭顟B(tài)下隨著溫度的降低，填料彈性逐漸消失，防漏性能隨之下降，由于介質(zhì)滲漏造成填料與閥桿處結(jié)冰，影響閥桿正常操作，同時(shí)也會(huì)因閥桿上下移動(dòng)而將填料傷，引起嚴(yán)重泄露。長(zhǎng)頸閥蓋結(jié)構(gòu)還便于纏繞保冷材料。

　　2. Valve cover: Adopting a long neck valve cover structure, its purpose is to protect the packing box, because the sealing of the packing box is one of the key factors for low-temperature valves, and there are leakage points at this location. This is because at low temperatures, as the temperature decreases, the elasticity of the packing gradually disappears, and the leak proof performance decreases. Due to medium leakage, the packing and valve stem freeze, affecting the normal operation of the valve stem. At the same time, the packing may be damaged due to the up and down movement of the valve stem, causing serious leakage. The long neck valve cover structure is also convenient for wrapping cold insulation materials.

　　3.閥瓣（閘板）：閘閥采用撓性閘板或開(kāi)式閘板；截止閥的平閥座及針形閥，采用塞子形閥瓣。這些結(jié)構(gòu)形式不論溫度如何變化，均能保持可靠的密封。

　　3. Valve disc (gate): The gate valve adopts flexible gate or open gate; The flat seat and needle valve of the globe valve adopt a plug shaped valve disc. These structural forms can maintain reliable sealing regardless of temperature changes.

　　4.閥桿：閥桿需鍍鉻、鍍鎳磷或經(jīng)氮化處理，以提高閥桿表面硬度，防止閥桿與填料、填料壓套相互咬死，損壞密封填料，造成填料函泄露。

　　4. Valve stem: The valve stem needs to be chrome plated, nickel phosphorus plated or nitrided to improve the surface hardness of the valve stem, prevent the valve stem from biting against the packing and packing sleeve, damage the sealing packing, and cause leakage of the packing box.

　　5.墊片：墊片選用應(yīng)考慮材料的低溫性能，如壓縮回彈性、予緊力、緊固壓力分布以及應(yīng)力松弛特性等。

　　5. Gasket: The selection of gaskets should consider the low-temperature performance of the material, such as compression resilience, preload force, tightening pressure distribution, and stress relaxation characteristics.

　　6.填料函及填料：填料函不能與低溫段直接接觸，而設(shè)在長(zhǎng)頸閥蓋頂端，使填料函處于離低溫區(qū)較遠(yuǎn)的位置，在0℃以上的溫度環(huán)境下工作，提高填料函的密封效果。填料函多采用帶有中間金屬隔離環(huán)的二段填料結(jié)構(gòu)，可以從填料函中間加入潤(rùn)滑脂形成油封層，降低填料函壓差。

　　6. Packing box and packing: The packing box should not be in direct contact with the low-temperature section, but should be placed at the top of the long neck valve cover, so that the packing box is located far away from the low-temperature area and works in a temperature environment above 0 ℃ to improve the sealing effect of the packing box. The stuffing box often adopts a two-stage stuffing structure with a middle metal isolation ring, which can add lubricating grease from the middle of the stuffing box to form an oil seal layer and reduce the pressure difference in the stuffing box.

　　7.上密封：低溫閥都設(shè)有上密封結(jié)構(gòu)，上密封要堆焊鈷鉻鎢硬質(zhì)合金，精加工后研磨。

　　7. Upper seal: Low temperature valves are equipped with an upper seal structure, which is welded with cobalt chromium tungsten hard alloy and polished after precision machining.

　　8.閥座、閥瓣、（閘板）密封面：低溫閥的關(guān)閉件采用鈷鉻鎢硬質(zhì)合金堆焊機(jī)構(gòu)。軟密封結(jié)構(gòu)由于聚四氟乙烯膨脹系數(shù)大，低溫下變脆，所以?xún)H使用溫度高于-70℃的低溫閥，但聚三氟乙烯可用于-162℃的低溫閥。

　　8. Valve seat, valve disc, (gate) sealing surface: The closing parts of low-temperature valves use cobalt chromium tungsten hard alloy welding mechanism. Due to the high expansion coefficient of polytetrafluoroethylene, the soft sealing structure becomes brittle at low temperatures, so only low-temperature valves with temperatures above -70 ℃ are used. However, polytetrafluoroethylene can be used for low-temperature valves with temperatures above -162 ℃.

　　9.中法蘭螺栓：

　　9. Middle flange bolts:

　　1）：螺栓應(yīng)有足夠的強(qiáng)度，因?yàn)槁菟ㄔ诜磸?fù)載荷下工作，常會(huì)因疲勞而產(chǎn)生斷裂。?? ? ? ? ? ? ? ? ? ? ? ? ? ? ??

　　1) Bolts should have sufficient strength because they often break due to fatigue when working under repeated loads.??  ? ?  ? ?  ? ?  ? ?  ? ?  ? ?  ? ??

　　2）：因螺栓在螺紋根部易引起應(yīng)力集中，所以最好采用全螺紋結(jié)構(gòu)的螺栓。10.保冷：又稱(chēng)隔溫板，是一塊焊在填料函下部長(zhǎng)頸部分的圓形板。提高保溫效果。

　　2) Because bolts at the root of the thread are prone to stress concentration, it is best to use bolts with a full thread structure. 10. Cold insulation: also known as insulation plate, is a circular plate welded to the long neck of the lower part of the packing box. Improve insulation effect.

　　11. 預(yù)防異常升壓的措施：?發(fā)生異常升壓現(xiàn)象時(shí)，會(huì)使閘板緊壓在閥座上，導(dǎo)致閘板不能開(kāi)啟。高壓會(huì)將中法蘭墊片沖出或沖壞填料；也可引起閥體、閥蓋變形，使閥座密封性能顯著下降。為防止異常升壓現(xiàn)象發(fā)生，一般低溫閥門(mén)在結(jié)構(gòu)上采用以下措施：

　　11. Measures to prevent abnormal voltage rise:? When abnormal pressure rise occurs, it will cause the gate to press tightly against the valve seat, resulting in the gate not being able to open. High pressure may cause the flange gasket to be flushed out or damage the packing; It can also cause deformation of the valve body and valve cover, significantly reducing the sealing performance of the valve seat. To prevent abnormal pressure rise, the following measures are generally adopted in the structure of low-temperature valves:

　　1） 設(shè)置泄壓孔，又稱(chēng)壓力平衡孔或排氣孔。

　　1) Set up pressure relief holes, also known as pressure balance holes or exhaust holes.

　　2）在閥門(mén)上設(shè)置引出管或安裝安全閥以排出異常高壓。

　　2) Install an outlet pipe or safety valve on the valve to discharge abnormal high pressure.

　　二.深冷處理

　　II cryogenic treatment

　　深冷處理：將零件浸入低溫液氮箱中保溫一定時(shí)間，以減少其由于溫差和金相組織改變而產(chǎn)生的變形，從而提高閥門(mén)在低溫時(shí)的密封性能的一種處理方法。

　　Cryogenic treatment: a treatment method that immerses parts in a low-temperature liquid nitrogen tank for a certain period of time to reduce deformation caused by temperature differences and changes in metallographic structure, thereby improving the sealing performance of valves at low temperatures.

　　1.在閥瓣和閥座的密封面上堆焊硬質(zhì)合金應(yīng)符合JB/T 6438的規(guī)定。使用溫度低于-100℃時(shí)，堆焊后要進(jìn)行深冷處理，即在研磨前浸在-196℃的液氮中保冷2-6h后取出自然處理，然后研磨裝配。

　　1. Welding hard alloy on the sealing surface of the valve disc and seat shall comply with the provisions of JB/T 6438. When the operating temperature is below -100 ℃, deep cooling treatment should be carried out after welding, that is, soaking in liquid nitrogen at -196 ℃ for 2-6 hours before grinding, then taking it out for natural treatment, and then grinding and assembling.

　　2.用于-100℃以下的低溫閥門(mén)，其閥體、閥蓋、閥瓣、閥座、閥桿等零件在精加工前應(yīng)進(jìn)行深冷處理，即將零件浸放在液氮箱中進(jìn)行冷卻，當(dāng)零件溫度達(dá)到-196℃時(shí)，開(kāi)始保溫1-2h，然后取出箱外處理到常溫，重復(fù)循環(huán)2次。

　　2. For low-temperature valves below -100 ℃, the valve body, valve cover, valve disc, valve seat, valve stem and other parts should undergo cryogenic treatment before precision machining. That is, the parts should be immersed in a liquid nitrogen box for cooling. When the temperature of the parts reaches -196 ℃, insulation should be started for 1-2 hours, and then the parts should be taken out of the box and treated at room temperature, repeating the cycle twice.

　　三.低溫閥門(mén)的試驗(yàn)方法

　　III Test methods for low-temperature valves

　　1、常溫試驗(yàn)：常溫試驗(yàn)應(yīng)符合GB/T13927、JB/T9092、API598及API

　　1. Room temperature test: The room temperature test should comply with GB/T13927, JB/T9092, API598, and API

　　6D的規(guī)定。

　　6D regulations.

　　2、低溫試驗(yàn)：低溫閥門(mén)的低溫試驗(yàn)在常溫試驗(yàn)合格后進(jìn)行。試驗(yàn)前應(yīng)清除閥體中的水和油脂，用符合試驗(yàn)要求的熱電偶與閥門(mén)連接，試驗(yàn)過(guò)程中監(jiān)測(cè)閥體、閥蓋的溫度。低溫試驗(yàn)冷卻介質(zhì)為液氮與酒精的混合液或液氮，試驗(yàn)介質(zhì)為氦氣。

　　2. Low temperature test: The low-temperature test of low-temperature valves shall be conducted after passing the normal temperature test. Before the test, the water and grease in the valve body should be removed, and a thermocouple that meets the test requirements should be connected to the valve. During the test, the temperature of the valve body and valve cover should be monitored. The cooling medium for low-temperature testing is a mixture of liquid nitrogen and alcohol or liquid nitrogen, and the testing medium is helium gas.

　　四.低溫閥門(mén)技術(shù)分解

　　4 Decomposition of Low Temperature Valve Technology

　　4.1　低溫閘閥

　　4.1 Low temperature gate valve

　　閘閥是指由一個(gè)滑動(dòng)的閥瓣或閘板通過(guò)閥桿由傳動(dòng)裝置驅(qū)動(dòng)，沿垂直于介質(zhì)流向運(yùn)動(dòng)的閥門(mén)。閘閥具有雙向密封、密封性能好、全開(kāi)狀態(tài)壓降小、適用的口徑及壓力范圍較寬等特點(diǎn)，在管道上主要用于切斷介質(zhì)，是工程中應(yīng)用最廣的閥門(mén)。低溫閘閥的典型結(jié)構(gòu)如圖1所示。

　　A gate valve refers to a valve that is driven by a transmission device through a sliding valve disc or gate through a valve stem, and moves along a direction perpendicular to the flow of the medium. Gate valves have the characteristics of bidirectional sealing, good sealing performance, low pressure drop in fully open state, wide applicable diameter and pressure range, etc. They are mainly used in pipelines to cut off media and are the most widely used valves in engineering. The typical structure of a low-temperature gate valve is shown in Figure 1.

　　低溫閘閥具有雙閥座，閥門(mén)關(guān)閉時(shí)閥腔內(nèi)會(huì)形成密閉的空間，為避免低溫閘閥出現(xiàn)閥腔超壓的問(wèn)題，通常采用在閘板上開(kāi)泄壓孔的方式來(lái)實(shí)現(xiàn)閥腔泄壓的功能，泄壓方向在開(kāi)泄壓孔的那一側(cè)；由于在閘板上開(kāi)了泄壓孔，低溫閘閥無(wú)法滿(mǎn)足雙向密封要求，只能實(shí)現(xiàn)單向密封，閥門(mén)關(guān)閉時(shí)，閥門(mén)的承壓（密封）方向與泄壓方向相反，因此低溫閘閥要根據(jù)關(guān)閉時(shí)的承壓方向確定安裝方向。另外，低溫閘閥具有延長(zhǎng)閥蓋結(jié)構(gòu)，并設(shè)置滴水盤(pán)。

　　Low temperature gate valves have dual valve seats, and when the valve is closed, a closed space is formed inside the valve chamber. To avoid the problem of overpressure in the valve chamber of low-temperature gate valves, a pressure relief hole is usually opened on the gate plate to achieve the function of pressure relief in the valve chamber, and the pressure relief direction is on the side where the pressure relief hole is opened; Due to the opening of pressure relief holes on the gate, low-temperature gate valves cannot meet the requirements of bidirectional sealing and can only achieve unidirectional sealing. When the valve is closed, the pressure bearing (sealing) direction of the valve is opposite to the pressure relief direction. Therefore, the installation direction of low-temperature gate valves should be determined based on the pressure bearing direction when closed. In addition, the low-temperature gate valve has an extended valve cover structure and is equipped with a drip tray.

　　4.2　低溫截止閥

　　4.2 Low temperature shut-off valve

　　截止閥是指啟閉件（閥瓣）由閥桿帶動(dòng)，沿閥座（密封面）軸線作升降運(yùn)動(dòng)的閥門(mén)。截止閥的閥桿開(kāi)啟或關(guān)閉行程相對(duì)較短，而且具有可靠的切斷功能，因此，非常適合作為切斷使用，也適合作為調(diào)節(jié)或節(jié)流使用。截止閥屬于閥瓣強(qiáng)制密封，開(kāi)啟和關(guān)閉時(shí)所需力較大，因此，對(duì)于大口徑和高壓管道一般不采用截止閥。低溫截止閥的典型結(jié)構(gòu)如圖2所示。

　　Globe valve refers to a valve whose opening and closing components (valve disc) are driven by the valve stem and move up and down along the axis of the valve seat (sealing surface). The stem of a globe valve has a relatively short opening or closing stroke and reliable shut-off function, making it very suitable for use as a shut-off valve, as well as for regulating or throttling. Globe valves belong to valve disc forced sealing, and require a large amount of force to open and close. Therefore, globe valves are generally not used for large-diameter and high-pressure pipelines. The typical structure of a low-temperature shut-off valve is shown in Figure 2.

　　低溫截止閥屬于單閥座密封，閥門(mén)關(guān)閉時(shí)閥腔內(nèi)不會(huì)形成密閉的空間，因此不需要設(shè)置泄壓裝置。低溫截止閥關(guān)閉時(shí)，閥門(mén)的承壓（密封）方向與常溫截止閥相同，沒(méi)有特殊安裝要求。低溫截止閥具有延長(zhǎng)閥蓋結(jié)構(gòu)，并設(shè)置滴水盤(pán)。

　　Low temperature globe valves belong to single seat sealing, and when the valve is closed, there will be no sealed space in the valve chamber, so there is no need to install a pressure relief device. When the low-temperature shut-off valve is closed, the pressure bearing (sealing) direction of the valve is the same as that of the normal temperature shut-off valve, and there are no special installation requirements. The low-temperature shut-off valve has an extended valve cover structure and is equipped with a drip tray.

　　4.3　低溫球閥

　　4.3 Low temperature ball valve

　　球閥的啟閉件是一個(gè)球體，利用球體繞閥桿的軸線旋轉(zhuǎn)90°實(shí)現(xiàn)開(kāi)啟和關(guān)閉的目的。球閥具有雙向密封、密封性能好、低流阻、結(jié)構(gòu)緊湊、操作方便等特點(diǎn)。管道上主要用于切斷、分配和改變介質(zhì)流動(dòng)方向，設(shè)計(jì)成“V”形開(kāi)口的球閥還具有良好的流量調(diào)節(jié)功能。低溫球閥的典型結(jié)構(gòu)如圖3所示。

　　The opening and closing component of a ball valve is a sphere that rotates 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing. Ball valves have the characteristics of bidirectional sealing, good sealing performance, low flow resistance, compact structure, and easy operation. The pipeline is mainly used to cut off, distribute, and change the direction of medium flow. The ball valve designed with a "V" opening also has good flow regulation function. The typical structure of a low-temperature ball valve is shown in Figure 3.

　　低溫球閥具有雙閥座，閥門(mén)關(guān)閉時(shí)閥腔內(nèi)會(huì)形成密閉的空間，為避免低溫球閥出現(xiàn)閥腔超壓的問(wèn)題，通常采用以下2種方式來(lái)實(shí)現(xiàn)閥腔泄壓功能：①在球體上開(kāi)泄壓孔的方式，泄壓方向在開(kāi)泄壓孔的那一側(cè)；②通過(guò)設(shè)計(jì)泄壓閥座來(lái)實(shí)現(xiàn)閥腔泄壓，泄壓方向可以是上游閥座方向，也可以是下游閥座方向。對(duì)于在球體上開(kāi)泄壓孔的低溫球閥，無(wú)法滿(mǎn)足雙向密封的要求，只能實(shí)現(xiàn)單向密封，閥門(mén)關(guān)閉時(shí)，閥門(mén)的承壓（密封）方向與泄壓方向相反，因此低溫球閥要根據(jù)關(guān)閉時(shí)的承壓方向來(lái)確定安裝方向。另外，低溫球閥具有延長(zhǎng)閥蓋結(jié)構(gòu)，并設(shè)置滴水盤(pán)。

　　Low temperature ball valves have dual seats, and when the valve is closed, a closed space is formed inside the valve chamber. To avoid the problem of overpressure in the valve chamber of low-temperature ball valves, the following two methods are usually used to achieve the pressure relief function of the valve chamber: ① opening a pressure relief hole on the ball, and the pressure relief direction is on the side where the pressure relief hole is opened; ② By designing a pressure relief valve seat to achieve valve chamber pressure relief, the pressure relief direction can be either the upstream valve seat direction or the downstream valve seat direction. For low-temperature ball valves with pressure relief holes on the sphere, the requirement for bidirectional sealing cannot be met, and only unidirectional sealing can be achieved. When the valve is closed, the pressure bearing (sealing) direction of the valve is opposite to the pressure relief direction. Therefore, the installation direction of low-temperature ball valves should be determined based on the pressure bearing direction when closed. In addition, the low-temperature ball valve has an extended valve cover structure and is equipped with a drip tray.

　　4.4　低溫蝶閥蝶閥的啟閉件是一個(gè)圓盤(pán)形的蝶板，在閥體內(nèi)繞其自身的軸線旋轉(zhuǎn)，從而達(dá)到啟閉或調(diào)節(jié)。蝶閥具有結(jié)構(gòu)簡(jiǎn)單、流阻小、啟閉迅速、啟閉力矩小、體積小、質(zhì)量輕等特點(diǎn)，但密封性能相對(duì)于閘閥較差，常用于密封要求不是很高的大口徑管道上。低溫蝶閥的典型結(jié)構(gòu)如圖4所示。

　　The opening and closing component of a low-temperature butterfly valve is a disc-shaped butterfly plate that rotates around its own axis inside the valve body to achieve opening, closing, or adjustment. Butterfly valves have the characteristics of simple structure, low flow resistance, rapid opening and closing, small opening and closing torque, small volume, and light weight. However, their sealing performance is relatively poor compared to gate valves, and they are commonly used in large-diameter pipelines with low sealing requirements. The typical structure of a low-temperature butterfly valve is shown in Figure 4.

　　低溫蝶閥關(guān)閉時(shí)閥腔內(nèi)不會(huì)形成密閉的空間，因此不需要設(shè)置泄壓裝置。低溫蝶閥關(guān)閉時(shí)，閥門(mén)的承壓（密封）方向與常溫蝶閥相同，沒(méi)有特殊安裝要求。低溫蝶閥具有延長(zhǎng)閥蓋結(jié)構(gòu)，并設(shè)置滴水盤(pán)。

　　When the low-temperature butterfly valve is closed, no sealed space will be formed inside the valve chamber, so there is no need to install a pressure relief device. When the low-temperature butterfly valve is closed, the pressure bearing (sealing) direction of the valve is the same as that of the normal temperature butterfly valve, and there are no special installation requirements. The low-temperature butterfly valve has an extended valve cover structure and is equipped with a drip tray.

　　低溫閘閥、截止閥、球閥及蝶閥具有延長(zhǎng)閥蓋、滴水盤(pán)等結(jié)構(gòu)特點(diǎn)，其中對(duì)于具有密閉閥腔的閘閥、球閥等閥門(mén)，需要在閥門(mén)上設(shè)置泄壓裝置。對(duì)于有延長(zhǎng)閥蓋的低溫閥門(mén)宜安裝在水平管道上，或應(yīng)在水平面上與水平面成不小于45°的方向操作閥桿。對(duì)于低溫截止閥、蝶閥其安裝流向與常規(guī)的閥門(mén)一樣；低溫閘閥、球閥具有泄壓裝置，閥門(mén)安裝后的泄壓箭頭應(yīng)指向閥門(mén)關(guān)閉狀態(tài)下壓力高的一側(cè)。針對(duì)石油化工裝置管道低溫閥門(mén)容易發(fā)生流向安裝錯(cuò)誤的問(wèn)題，建議從工藝和管道設(shè)計(jì)、閥門(mén)制造、安裝施工、運(yùn)行管理等環(huán)節(jié)入手，確保低溫閥門(mén)的正確安裝。

　　Low temperature gate valves, globe valves, ball valves, and butterfly valves have structural characteristics such as extended valve covers and drip trays. For gate valves, ball valves, and other valves with closed valve chambers, pressure relief devices need to be installed on the valves. For low-temperature valves with extended valve covers, they should be installed on horizontal pipelines, or the valve stem should be operated in a direction not less than 45 degrees from the horizontal plane. For low-temperature globe valves and butterfly valves, their installation flow direction is the same as that of conventional valves; Low temperature gate valves and ball valves have pressure relief devices, and the pressure relief arrow after valve installation should point to the side with higher pressure when the valve is closed. It is recommended to start with process and pipeline design, valve manufacturing, installation and construction, and operation management to ensure the correct installation of low-temperature valves in petrochemical equipment pipelines, which are prone to flow direction installation errors.

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