艉轴空气型密封装置简介与管理要点

船舶尾轴空气密封修船注意事项
1. 嘿，你知道吗，船舶尾轴空气密封修船的时候，一定要仔细检查密封件啊！就像你爱护自己的宝贝一样，可不能马虎！比如说，你总不会随便对待你心爱的手机吧？
2. 修船的时候，千万别忘了给尾轴来个全面的“体检”呀！这可关系到船舶的安全呢，就好比人的身体，一处小毛病都可能引发大问题，你说是不是？
3. 注意啦，在安装新的空气密封时，要像给公主穿新衣一样小心翼翼啊！你想想，要是不小心弄破了，那可就糟糕了，就像新衣服被扯坏了一样心疼。

4. 哎呀呀，修船师傅们可别粗心大意哦！对船舶尾轴空气密封的处理要格外用心，这可不是闹着玩的，好比建房子，根基不稳怎么行呢？
5. 大家在修船时，一定要确保密封安装到位啊！这就像给门安装锁一样，没安好可就不保险啦，你能放心吗？
6. 嘿，别忘了检查密封的周边环境呀！就像你出门要看看天气适不适合一样重要，要是有问题不及时处理，那后果不堪设想呢！
7. 修船的时候，对尾轴空气密封的每一个细节都不能放过啊！这就好像拼图，少一块都不行，你说对不对？
8. 注意哦，处理密封的时候动作要轻柔些呀！可别像个糙汉子似的，不然弄坏了可咋办，就像对待易碎的花瓶一样呀！
9. 哇塞，修船可真是个技术活呀！特别是船舶尾轴空气密封，一定要高度重视，这可关系到整艘船的命运呢，能不认真对待吗？
10. 最后啊，大家一定要牢记这些注意事项，把船舶尾轴空气密封修得妥妥当当的！让我们的船能安全航行，这多重要啊！
我的观点结论就是：船舶尾轴空气密封修船马虎不得，必须认真对待每一个细节，才能确保船舶的安全和正常运行。

KOBELCO空气式尾轴密封KOBELCO空气式尾轴密封大连远洋公司船技部富强【内容提要】此文介绍KOBELCO空气式尾轴密封形式的基本设计,工作原理和基本组成,并借助图纸介绍安装此设备时的检查注意事项和密封检查方法.l简单介绍为防止海水污染,KOBELCO公司设计制造了空气式尾轴密封装置.该密封装置的艏部(FWD)密封结构与以往KOBELCO紧凑密封的结构相同,艉部()空气式轴封的结构如图1所示(P4型).图1AFT轴封的结构(P4型)该轴封是通过在金属外壳凸缘上方的空气喷管把空气放出,排进海水里.空气喷管是"止回"式的,一旦空气停止放出,海水也不会从喷管侵入.利用放出的空气来检测船舶吃水的变化,然后根据吃水的变化产生的压力,以调整空气流量与油管的油压,从而防止海水侵入船内和润滑油流出船外.同时,各密封环所承受的压力也减小而能保持良好性能.其特长为:(1)各密封环所承受的负荷量明显减小,同时,海水侧,轴管侧都有两根密封环装置,提高了可靠性.一旦密封环破损,船尾管内的润滑油或海水会通过空气室被收回到船内,不会有油流出船外或海水侵人尾轴管内的可能性;(2)维修保养简单,在设定了空气流量和2#/3#密封环之间的空气压力之后,操作系统自动化工作,避免了根据吃水的变化来转换油柜的操作方式;(3)空气消耗量较小,基本设定在40～60L/min;(4)如遇空气压力控制单元发生故障,只要备有重力油柜,便能将空气密封转变成普通的防油密封环.2基本设计船尾管内的管道为4根(P4型),位于顶部的排气管和通往NO.2/3之间的供气管的材质是铜管;位于底部的来自NO.2/3之间的排油回收管和NO.3/3s之间的供油管可以是铜管,也可以是不锈钢管.供气装置到空气密封装置之间的管道基本用铜管将空气供到空气控制单元.S/T油罐的容量由船尾管内的容量决定,大致数值如下表,油罐的设置在高出尾轴中心线3m左右的高度.轴封尺寸(ram)S/I"油罐的容量(L)670以下10071O以下2oo在紧急情况发生时,为了能够简单转换为旧式轴封,在S/T出口管上安装分歧管.回流管的高度应比海水水压高出0.2～0.3kg/cm.3工作原理该密封系统主要由以下部分组成:空气压力控制单元:用于控制和调节的压缩空气进入该单元,该装置内置的控制机件和设置在厂家出厂前已经调节完毕, 使用中仅仅检查阀门的开,关状态即可;油压单元:一般有2台齿轮油泵,一台保持连续运转,对油柜施加压力;海水和油回收单元:用于回收油水,该单元一般位于船底;S/T油柜:管道配置系统如图2所示.从图2可以看出,这种结构通过排气检验船舶吃水的变化,根据吃水的变化对密封环的空间和船尾轴油管施加最为合适的压力,从防止海水进人船内和滑油漏出船外.各部位的压力条件如表1所示:表1各部位的压力条件结构海水NO.1NO.2NO.3NO.4尾管油流体海水(滑滑油)空气油油1.O1.O1.O1.31.3压力kg/emkg/emkg/emkg/cmkg/em控制空气气压空气压+空气压+方法油压油压管道无供气#油油入口油入口/出口NO.2/3之间:从凸缘环上排气检测出海水压力,以此施加与海水压力相同的空气压力.进入NO.2/3 之间的海水或油,通过排油回收管被回收到船内.N0.1/2之间:没有安装来自船内的管道.因此,NO.1/2之间的压力几乎与海水压力相同.在此空间通常为海水与空气的混合状态.船尾轴管内:在轴心约施加0.25kg/cm油压的地方安装重力柜.对这个重力柜施加与海水压力同样的空气压力.KOBEI』c0空气式尾轴密封——富强NO.3/3S问:由于使用泵对船尾管重力油柜的油进行循环,因此压力与船尾管相同.4安装检查在新造船和拉尾轴的修理时,都会涉及到安装检查问题.无论在什么情况下,管系和各个单元的安装已经完毕,主要检查各个装置与空气式轴封的连接是否正确,空气控制装置的接头都有编号,按照编号对照连接部位没有错误即可.因此,管理人员检查的重点是管系的清洁和密封情况.一般在安装轴封前,必须用压缩空气冲洗循环油管和空气管.此后,对各个部位密封试验认真检查.密封检查分两个主要部分:(1)空气管和循环油管的泄漏试验a)从船尾隔壁到船尾轮毂之问的管道试验方法,用塞子插在轮毂放气出口,即关闭此出口,然后向管内提供约3.0kg/cm的空气压力,在10分钟内不可有压力明显下降的现象,检查后,务必拔出塞子.b)空气管泄漏试验,来自空气控制装置的空气压力已经经过减压阀调整,从空气控制装置向管路供约3.0kg/cm的空气压力,检查以下各项:①排气管(仅限P4型)检查压力下降情况,进行10分钟左右.②关闭NO.2/3之间人口管路上的阀门,使用空气控制装置P5压力表进行检查,进行1O分钟左右.③在管道接头部位抹肥皂水,检查有无漏泄.C)循环油管泄漏试验,向尾轴管和NO.3/3s之间加油后,施加相当于应急时使用S/T重力柜的压力, 检察管道接头部位有无漏油..(2)船尾管和轴封装置的供油及密封试验a)船尾管的供油及NO.3s密封环的泄漏,给船尾管加油,然后转换到应急用S/T油柜的循环油管上(操作方法参阅使用说明书和管道系统图).注意先不要向NO.3/3s之间加油.取下船尾轴封装置NO.3/3s 之间的插塞,检查从NO.3s密封环处有无漏油.b)NO.3/3s之间的供油和NO.3密封环的漏泄图2试验,①插上船尾密封装置NO.3/3s之问底部的插塞,取下顶部的插塞.②打开No.3/3s之间管道上的阀门,向此空问加油,加到顶部时停止加油,然后检查NO.3密封环有无漏油.检查方法有两个,其一,从NO.3/3s之问的顶部插塞处检查NO.3/3s之问油空间的油面有无下降,试验结果1O分钟不下降为好.其二,插上N0.3/3s之问顶部的插塞,施加应急时用S/ T重力柜的油压.取下NO.2/3之问底部的插塞,检查NO.3密封环处有无漏油.c)前侧轴封的供油及漏泄试验,这与以往油封式轴封的检查相同.①向船尾管加油后,取下艏密封NO.4/5之问底部的插塞,检查从N0.4密封环处有无漏油.②检查NO.4密封环处没有漏油后,向No.4/5之间加油,加油后检查从NO.4密封环处有无向前侧漏油以及圆环处有无漏油.供油后到进水前以及进水后装机期间,注意千万不要从空气控制装置排气.5运转前的操作(1)按照说明书检查各个装置以及与其连接的管道上阀门的开关状态.(2)慢慢打开空气控制装置的空气总阀,开始供气.供气之前,必须将空气中的杂质排放掉.(3)后侧轴封装置的压力调整在设备厂家已经调整完毕.如发生与使用说明书所要求的压力条件不符时,应要求厂家进行调整.<航海技术)2004年第5期。

简述空气密封型艉轴密封装置的应用摘要：本文以ax型艉轴密封装置为例，简述空气密封型艉轴密封装置在现代船舶上的应用。

关键词：空气密封; ax型; 船舶abstract：this paper introduces the application of ax type air seal stern tube bearing system at modern ship. keywords：air seal；ax type；ship中图分类号：[o355] 文献标识码：a 文章编号：1 前言艉轴密封装置能保证艉轴在运转中有下沉、径向跳动及偏心转动、轴向窜动等情况时具有良好的密封性，有效隔离滑油和海水、泥沙，防止艉管滑油泄漏或是海水灌入机舱，所以艉轴密封装置工作性能的好坏，直接影响船舶能否正常营运。

目前新造的大中型舶船上广泛采用空气密封型艉轴密封装置，它是传统的“simplex”型艉轴密封装置的改进型，是目前比较先进的船舶艉轴密封装置。

本文以某新造远洋货轮为例，该轮设计吃水18.1米，船体基线至轴系中心线高度5米，安装了伊格尔工业株式会社-kemel公司生产的ax型艉轴密封装置，使用0.7mpa的压缩空气作为工作气源，冲洗水由船上的淡水压力柜供给。

结合实际情况，对ax型艉轴密封装置的结构特点、日常操作注意事项等进行介绍、分析。

2 ax型艉轴密封装置的特点和工作原理2.1 密封装置的特点ax型艉轴密封装置由前密封和后密封装置组成，具有其独特的优点，比如：1、可靠性和安全性高；2、结构紧凑并且易于操作；3、维护保养简便；4、空气消耗量少；5、带有防渔网功能，减少进坞维修费用；6、根据吃水自动调整压力，确保密封性能。

2.1.1 前密封装置图1所示，前密封装置的结构基本上与后密封装置相同，不同的是前密封装置只有#4、#5两道密封环。

密封环的作用是把滑油密封在艉管和轴承区域的油腔中，阻止滑油泄漏。

装置中的衬套通过螺栓上紧的夹紧环安装在艉轴上，随轴的旋转而转动。

船用艉轴密封
船用艉轴密封是一种用于船舶尾部轴承密封的装置，主要
用于防止海水进入船舶的机舱。

它通常由以下几个部分组成：
1. 艉轴密封壳体：密封壳体是安装在船舶艉部的一个金属
外壳，通常由高强度和耐腐蚀的材料制成，如不锈钢。

密
封壳体具有良好的密封性能，能够有效防止海水进入机舱。

2. 密封垫片：密封垫片是安装在密封壳体内部的一个重要
部件，通常由弹性材料制成，如橡胶。

密封垫片能够与轴
承紧密接触，并形成密封效果，防止海水渗入。

3. 密封油：密封油是填充在密封壳体内部的润滑油，通常
为高温、高压和耐腐蚀的润滑油。

密封油能够在轴承和密
封垫片之间形成一层润滑膜，减少摩擦和磨损，同时也能
起到密封作用。

4. 密封装置：密封装置包括密封环、密封垫、密封圈等，
用于确保密封的完整性和稳定性。

这些密封装置通常由耐
腐蚀和耐磨损的材料制成，如橡胶和金属。

船用艉轴密封的工作原理是，当轴承转动时，密封垫片与
轴承紧密接触，并形成一层密封效果。

同时，密封油在密
封壳体内形成一层润滑膜，减少摩擦和磨损。

当海水试图
进入机舱时，密封垫片和密封装置会阻止海水的渗入，保
持机舱的干燥和安全。

船用艉轴密封在船舶的设计和制造中起到了至关重要的作用，它能够有效保护船舶的机舱免受海水的侵蚀，提高船舶的安全性和可靠性。

同时，船用艉轴密封还能减少轴承的磨损和故障，延长轴承的使用寿命，降低维修和更换的成本。

船舶尾轴密封装置原理及漏泄处理一、引言船舶尾轴密封装置是船舶轴系的重要部件之一,其性能好坏直接影响到船舶的运行,同时对防止尾轴滑油污染海洋环境也起着十分重要的作用,因此对尾轴密封装置的研究是极其必要的。

笔者所在的船舶,大风浪天气航行时突发机舱尾轴密封油柜高位报警,后经检查发现,是尾轴密封不良导致海水漏泄至密封油腔里,引起密封油柜高位且乳化。

船舶尾轴密封油漏泄有两种情况常见:一是大风浪天气,船舶尾吃水小,由于船体剧烈震动,就会引起密封装置密封不好;二是船舶长时间锚泊,主机启动时有时会引起尾轴密封不好,从而导致漏泄。

尾轴密封不好导致漏泄一般分为:海水进入油腔造成密封油柜油乳化,最终导致尾轴腐蚀,或者密封油柜的油漏泄至船舷外,导致油污染水域。

无论哪种情况,都会造成不良的后果。

因此,必须重视船舶尾轴密封情况,一旦发生漏泄,就要及时采取正确措施。

二、船舶尾轴密封装置1.现代尾轴密封的特点目前海船的尾轴承绝大部分以油润滑的白合金轴承替代铁犁木等传统的水润滑轴承,其油膜承载能力大,油的润滑性能好,尤其是其密封装置能有效地密封,使海水和泥沙不易进入尾轴管,所以磨损很小,主机和轴系的工作相对平稳、可靠。

2.尾轴密封的结构尾轴密封装置分前密封装置(SC2Z)和后密封装置(SC2B)。

前密封装置位于机舱一端,其作用是防止尾轴管内的润滑油泄漏到机舱;后密封装置位于螺旋桨一端,其作用是既防止尾轴管内滑油泄漏到舷外污染海面,又防止海水进入尾轴管内乳化润滑油。

后密封装置一般有三道密封环(1号、2号和3号),后面两道密封环(1号、2号)的作用是防止海水进入尾轴管内,第三道密封环(3号) 的作用是防止尾轴管内滑油泄漏(见图1)。

前密封装置的结构与后密封装置的结构基本相同,不同的是前密封装置只有两道密封环(V1、V2)(见图2)。

密封环是由丁晴橡胶图2前密封装置的两道密封环(NBR)或氟橡胶(VITON)制成的,可根据不同的使用条件选择使用。

Advanced Technology of Propeller Shaft Stern Tube SealSeiji Yamajo , Dr. Eng.Iwao Matsuoka_____________________________________1Technical Director, KOBELCO MARINE ENGINEERING2-3-1, Shinhama Arai-cho, Takasago, 676-8670, Japan2KOBELCO MARINE ENGINEERING2-3-1, Shinhama Arai-cho, Takasago, 676-8670, JapanABSTRACTThe paper outlines the details concerning historical perspective and recent developments to meet a requirement that lube oil and seawater leakage must be prevented under any circumstances. Using a compressed air chamber, the lube oil in the stern tube is completely separated from seawater by providing a controlled “buffer zone” between lip type sealing rings. A constant quantity of compressed air supplied from within the ship, passes through the air chamber and is spouted into the sea. An air control unit automatically detects any change of draft level and adjusts the pressures to maintain the optimum pressure on each sealing ring. The key mechanism to detect the draft change correctly and to adjust the pressure balance is explained. Specific design and project applications for the stern tube air seal on ocean going and other marine vessels using line shaft propulsion and pod propulsion are explained.INTRODUCTIONIn most mid and large size merchant ships, an oil lubricated stern tube bearing system is applied. There are various kinds of seal systems used, such as lip type or mechanical type for oil lubricated stern tubes. The basic function is to prevent oil leakage from and seawater penetration into the stern tube. The most popular oil lubricated seal is a lip type seal and an example is shown in Fig. 1. The oil pressure in the stern tube is 0.03 Mpa (0.3 bar) higher than seawater pressure and oil pressure in the #2/3 chamber is designed to be lower than seawater pressure. One of the reasons to provide a piping line to the #2/3 seal chamber is to drain both leaking oil and penetrated seawater from #2/3 seal chamber.In the traditional seal system, stern tube oil is separated from seawater by plural sealing rings and some quantity of oil and seawater leakage through the sealing rings is inevitable.Many kinds of air seals were developed to solve this problem (Rawland,B.) (Shiomi et. al.) (Kuwabara et. al.). In this paper we define the air seal. There is an air chamber in the aft stern tube seal and the stern tube oil is separated from seawater by this air chamber. We will introduce various legacy designs of air seals. Then the mechanism of air seal, which is classified as “constant air flow type”, is explained in detail. We will also show an example application of the air seal to the pod propulsion.Fig.1 Structure of lip type stern tube sealHISTORY OF AIR SEALSeparation of Oil and SeawaterAccording to our definition of an air seal, the first air seal is the [Coastguard Sternseal System] ®, shown in Fig. 2(Catalogue, Japan Marine Technologies Ltd.) which was developed in 1970. A mechanical face seal is provided to prevent seawater ingress combined with a lip seal, which is provided to prevent oil leakage. In case of seawater ingress through the face seal, it can be drained to a drain tank through a drainage pipe connected to the air chamber. The air pressure in the air chamber is 0 Mpa (0 bar) because it is connected to the ambient air in the engine room.Fig. 2 [Coastguard Sternseal System] ®Constant Air Pressure Type[Stern Dry Seal EVS-1] ® was developed in 1983 and the schematic piping is shown in Fig. 3 (Catalogue, Eagle Industry Co., Ltd.). Compressed air is supplied into an air chamber between two segment mechanical seals and the air pressure is maintained constantly to be 0.03 Mpa (0.3 bar) higher than seawater pressure. Additional air must be supplied to maintain the above constant air pressure when air leakage increases through the segment seals and the air pressure between the seals decreases. The key concept of this seal is to keep the air pressure constant and that is why it is classified as a constant air pressure type. The leaking oil and seawater can be drained inboard through a drain pipe.Fig. 3 [Stern Dry Seal EVS-1] ®The next types of air seals were developed around 1990, after the two air seals mentioned above. We classify [Airspace Seal 1] ® shown in Fig. 4 (Catalogue, Blohm + Voss) is a constant air pressure type. There is a constant air pressure in the space II which is set at 0.01 Mpa (0.1 bar) below the ballast seawater pressure so that no air flows into the seawater. In order to drain leaking oil and seawater, which has accumulated in the air chamber, to the bilge, a solenoid valve is opened at certain intervals, with the pressure condition in the air chamber remaining unchanged.The main difference between the above two types of constant air pressure seals is that the air pressure in the air chamber is higher or lower than seawater pressure.Fig 4 [Airspace Seal 1] ®Constant Air Flow TypeAs an improvement to the aforementioned designs, the constant flow type of seal was designed. An example is shown in Fig. 5. A constant quantity of air supplied from the air source, which then passes through the #2/3 seal chamber and is then spouted into sea. The air pressure is always maintained about 0.01 Mpa (0.1 bar) greater than the seawater pressure so to slightly exceed the tightening force of the #1 and #2 sealing rings. The air pressure is added to stern tube oil tank, which is installed at 3m (0.03 Mpa) above a shaft center. The stern tube oil pressure becomes “air pressure in the #2/3 chamber + 0.03 Mpa (0.3 bar)” and it also follows the draft change. Any draft change can be automatically detected and both the air pressure in the #2/3 chamber and the stern tube oil pressure follow the draft change instantly. Accordingly all pressure differences on the aft sealing rings are always negligible. Leaking oil and seawater can be drained from the #2/3 chamber. In order to drain any leaking liquid smoothly, a small quantity of air is always blown through a flow controller on the drain tank. There are two advantages of the constant air flow system. One is that seawater rarely comes into the #2/3 chamber because the air pressure is always greater than seawater pressure. The other is that the life of sealing rings, especially the #1 and #2 rings, increases because of the small pressure difference maintained.Fig. 5 [KOBELCO Air Seal] ®THEORY OF CONSTANT AIR FLOW TYPE Structures of Air regulator and Flow controller It is shown in detail why the air pressure in the #2/3 seal chamber can follow changes in seawater pressure well with the constant air flow type. There are two important points in the system.The air pressure in the #2/3 seal chamber must be higher than seawater pressure. The air pressure from the air source is usually 0.7 Mpa (7 bar). It is reduced by an air regulator to 0.3~0.4 Mpa (3~4 bar) against seawater pressure of 0.05~0.2 Mpa (0.5~2 bar) to easily control the air flow. The function of the air regulator is to reduce the source air pressure and to keep it constant. For example, at 0.3 Mpa. The regulator structure is shown in Fig. 6 (Catalogue, SMC). Adjusting a spring below the diaphragm can reduce the source air pressure.Fig. 6 Air regulatorThe air flow rate of 40 Nl/min. (20~60 Nl/min.) which we recommend is a value determined after extensive experiments and field service. The air pressure in the #2/3 seal chamber becomes “seawater pressure + tightening force of sealing rings” with the recommended air flow condition and seawater pressure can be correctly detected. The air pressure in the #2/3 seal chamber becomes greater than the above “seawater pressure + tightening force of sealing rings” in case thequantity of air flow is much greater, such as 100 Nl/min. However, we cannot ignore the large quantity of air consumption from an economic viewpoint. In the case that the air flow is less than 10 Nl/min., seawater ingress into the #2/3 seal chamber may occur if the #1 and #2 sealing rings are damaged. It would eliminate a key advantage of the air seal. The structure of Flow controller is shown in Fig. 7(Catalogue, SMC).Fig. 7 Flow controllerThe air flow is controlled by changing the clearance between “body” and “needle” after the air pressure is reduced to 0.3~0.4 Mpa. The quantity of air flow is noted to be constant in this paper however practically is not constant in a strict sense. The quantity of air flow depends on a pressure difference between In side and Out side pressures in Fig. 7. The exact quantity is expressed by equation (1).When P1 is set to be 0.3 Mpa and P0 , which is almost the same as seawater pressure, is 0.1 Mpa (draft of 10m) the original air flow is adjusted to be Q = 40 Nl/min. The air flow changes between 45 Nl/min. and 35 Nl/min., when the draft changes from 5m to 15m. This air flow change is negligibly small considering the performance of the air seal and we therefore classify it a constant air flow type.Why Air Pressure in #2/3 Chamber Follows Seawater PressureWhen seawater pressure is constant, the air pressure in the #2/3 seal chamber is always higher than the seawater pressure. It becomes “seawater pressure + tightening force of #2 sealing ring”. Refer to Fig. 8-1.When the seawater pressure increases, the air flow from the #2/3 seal chamber to the sea stops momentarily. The air pressure in the #2/3 chamber increases because compressed air is continuously supplied to the #2/3 chamber. Then the air starts to flow again from the #2/3 seal chamber to the seawater by lifting the #2 sealing ring. The time interval when the air flow stops is momentary. For example about 0.4 sec. when the draft changes from 5m to 8m. Refer to Fig. 8-2.Equation (1)Q = k v∆PWhere Q : Quantity of air flow∆P = Pressure difference ∆P = P1 – P0P1 = Air pressure of In sideP0 = Air pressure of Out sidek = coefficientWhen the seawater pressure decreases, the air pressure in the #2/3 seal chamber decreases at the same time. Because in this case, the air pressure in the #2/3 seal chamber becomes greater that the “seawater pressure + the tightening force of the sealing rings” due to the decrease of the seawater pressure. More air flows from the #2/3 seal chamber to the sea by lifting the #1 and #2 sealing rings and the air pressure in the #2/3 seal chamber completely follows the decrease of seawater pressure. Refer to Fig. 8-3.The practical maximum wave condition where ocean going merchant ships can be operated without serious problems is of amplitude ±3m and frequency of 20 sec. The time delay of 0.4 sec. (as shown in Fig. 8-2) is negligible compared with the above wave condition. Consequently the air pressure in #2/3 chamber can follow wave induced seawater pressure change well. Refer to Fig. 8-4.Fig. 8 Mechanism by which air pressure in the #2/3 chamber follows seawater pressurePressure In Stern TubeThe air pipe to the #2/3 seal chamber is connected to a closed stern tube gravity oil tank of which volume is about 100 liter and the air pressure in the #2/3 seal chamber is added to the gravity tank. The oil pressure in the stern tube gravity tank completely follows the seawater pressure. There are no time lags in each pressure change due to wave conditions as shown in Fig. 9.Fig.9 Pressure curve due to wave change in ideal conditionPractically, the stern tube oil is usually circulated through long pipes and oil grooves in the stern bush. Thus a time lag would be expected between changes in the oil pressures near #3S ring and in the gravity tank when the draft changes by a wave. Actually waves cause a difference of pressure between the air pressure in the #2/3 seal chamber and the stern tube oil pressure near the #3S ring. Actual results depend on each ship respectively. A test was carried out on size 670 test equipment shown in Fig. 10 with a piping diagram as in Fig. 5. It was very important to imitate the structure of a practical stern tube. The volume of stern tube oil is designed to be about 600 liters in the test equipment. Fig. 11 shows one of the test results. The stern tube oil pressure becomes slightly out of the air pressure curve in the #2/3 seal chamber under the tested wave condition (Amp. = ±3m, T = 20sec.). However, the condition that the stern tube oil pressure must always be higher than the air pressure in the #2/3 seal chamber, to avoid continuous air leakage into stern tube is maintained. This proved that there are no technical problems in the practical operation.In the practical design, it is necessary to give a careful consideration to the installation of oil pumps and designing of oil pipes to avoid imbalance of the stern tube oil pressure.Fig. 10 Size 670 test equipmentFig. 11 Pressure curve due to wave in a practical conditionAir RelayA stern tube oil tank is provided at 3m above the shaft center and the stern tube oil pressure is designed to be 0.03 Mpa (0.3 bar) higher than the air pressure in #2/3 seal chamber. In case it is difficult to provide an oil tank at 3m above the shaft center in a practical ship, the oil tank can be installed at any convenient place by including an air relay in the air control unit. In the above case, in order to keep an adequate pressure difference on the #3 sealing ring, which is positioned between air and oil, the air pressure in #2/3 seal chamber should not be added to the stern tube oil tank directly. It is necessary to adjust the air pressure in #2/3 seal chamber and the adjusted air pressure should be added to the oil tank. The Air relay is a device to adjust the air pressure and an example isshown in Fig. 12(Instruction Manual, Fairchild). The air pressure in the #2/3 seal chamber is sent to the air relay as a pressure signal. Then the pressure signal is revised properly by setting an adjusting valve. The adjustable range is –0.12~+0.07 Mpa on the air relay. The revised pressure signal isadded to the stern tube oil tank and the air pressure in the oil tank can be controlled to be “air pressure in #2/3 seal chamber + revised pressure”. Compressed air is supplied to the oil tank when the signal pressure rises up and air is discharged from the oil tank when it goes down.Fig. 12 Air relayCONVERSION INTO AIR SEAL ON EXISTING CONTAINER SHIPThe main characteristics of KOBELCO Air Seal ® are to make the life of sealing rings longer and to prevent seawater coming into the #2/3 seal chamber. In addition to these characteristics, it has excellent performance against shaft vibration and the practical example is introduced. A container ship of which the specification is shown in Table 1 was built in 1998. A conventional oil seal (Seal size is 1060mm) was adopted on the ship and the piping diagram is shown in Fig. 13. Large axial shaft vibration was found at the sea trial and pressure fluctuation was caused in the aft stern tube recess because the oil in the recess was compressed by the axial movement of liner as shown in Fig. 14. This pressure fluctuation was propagated to the #2/3 seal chamber through the movement of the #3 and #3S sealing rings. (Miyashita) (Yamajo). Consequently the oil pressure in the #2/3 seal chamber momentarily becomes higher than the stern tube oil pressure as shown in Fig. 15. The oil in the #2/3 chamber leaks into stern tube by lifting the #3 sealing ring.Table 1 Specifications of a Container ShipFig. 13 Piping diagram of conventional oil seal (Size 1060)Fig. 14 Mechanism of pressure fluctuation caused by axial shaft vibrationFig. 15 Pressure curve caused by large axial shaft vibrationThe conventional oil seal was converted into an air seal to solve the above problem when the ship was docked in 2002. There were four pipes installed in the stern tube of container ship as shown in Fig. 12. It was not absolutely necessary to install an additional pipe for the conversion. An Air control unit, L.O. tank unit and Drain tank unit were provided to the existing system. It was confirmed at the sea trial, that after the conversion, the oil leakage could be stopped completely. We can note two reasons why the oil leakage problem could be solved by the conversion to the air seal. (1)The #2/3 chamber is filled with air in the air seal and there are no pressure fluctuations. (2)When the air pressure in #2/3 chamber becomes higher than the stern tube oil pressure, small quantity of air leaks into the stern tube. The air in stern tube reduces the pressure fluctuation in stern tube. The air is circulated in the stern tube and returns into #2/3 chamber through the stern tube L.O. tank. APPLICATION TO POD TYPEPROPULSIONRecently electric type pod propulsion has been developed and applied to many ships as well as the conventional mechanical type propulsion. There are different kinds of issues when the constant air flow type air seal is applied to the pod propulsion. The design concept is the same as with conventional stern tube air seal in that compressed air is spouted from the #2/3 seal chamber and the air pressure in #2/3 seal chamber is added to an oil tank. However, there is no stern tube in podpropulsion and some changes have been made to apply the air seal for the pod propulsions. ABB’sAzipod ® is an electric type pod propulsion and was provided for two ice breaking tankers “TEMPERA” and “MASTERA” which have been in service from 2002. Fig. 16 shows the piping schematic of the constant air flow type seal installed on the Azipod. A drain tank was provided below the shaft center in the pod and a gravity oil tank was provided at 3m above the shaft center. An oilchamber between #3 and #4 sealing rings is equivalent to the stern tube of merchant ships.Fig. 16 Schematic piping of seal for Azipod ®In case there is insufficient space to install a drain tank at the bottom part, one solution is to provide a solenoid valve in the drain line instead of the drain tank as shown in Fig. 17. Any oil and seawater that penetrates the #2/3 seal chamber can be drained by periodically opening the solenoid valve. This idea, however, is available only when the seawater draft from shaft center is less than 5m. Any oil and seawater that penetrates can be drained sufficiently when the opening time of solenoid valve is long enough. On the other hand, if the valve is opened too long, the air pressure in #2/3 seal chamber goes down and large pressure differences are put on #2 and #3 sealing rings. According to our test results, it is recommended to open the solenoid valve for 3~10 seconds. The operation is done a few times a day.Fig. 17 Solenoid valve instead of drain tankCONCLUSIONThe application of air seal will increase in future from a viewpoint of pollution free seal system. We have already supplied the constant air flow type seal to more than 150 ships and obtained excellent service results on all ships. The application of the air seal has been limited to stern tube seals of merchant ships until now. The subject air seal, however, has proved to be very effective to the electric pod propulsions. The application to the other types of propulsion would be expected to increase from now on.REFERENCESRawland,B. "The Evolution of a Pollution-Free Stern Sealing System for Ships", 44th Society of Tribologists and Lubrication Engineers, May 1989. Shiomi, S., Suzuki,T., Kudo,Y., Ikeda,M., Yazawa,H. and Hirabayashi,M. "Sealing Status of Newly Developed Stern Tube Seals in Practical Application to Ships", 42nd Society of Tribologists and Lubrication Engineers, May 1987. Kuwabara,T., Miyazaki,J., Takayasu, M., and Nishino,M. "Stern Tube Air Seal - Air Guard 4AS", Journal of Marine Engineering Society in Japan (in Japanese), Vol. 25, No. 6, 1990.Catalogue, Japan Marine Technologies Ltd.Catalogue, Eagle Industry Co., Ltd. E09-103B/86.03Catalogue, Blohm + Voss AG. HamburgCatalogue, SMC, Best Pneumatico 3Instruction Manual, Fairchild, Pneumatic and electro pneumatic applicationsY. Miyashita, "Recent Development with Stern Tube Sealing System on Large Ships", IME/SPE Joint Meeting in New York on April 9, 1975.S. Yamajo, "Study on Stern Tube Sealing System", Journal of Marine Engineering Society in Japan, March 1977.。

船舶尾轴密封知识学习船舶尾轴密封的发展展望第一章绪论在采用螺旋桨推进的船舶中，尾轴和尾轴承之间要按一定的规定留有间隙，尾轴又处于水面以下，工作时需要润滑和冷却，因此为了防止海水沿螺旋桨轴流入船内及润滑油泄漏，在尾轴管中必须设置密封装置。

尾轴密封装置的工作环境和条件极其恶劣，其在工作时不仅受到由轴系转动带来的磨损外，轴系自然下沉产生产生的不均匀作用力的影响，主机正倒车时尾轴还会产生一定的横向和轴向震动，这些都会对尾轴密封装置造成不良影响。

尾轴密封装置是船舶轴系的重要部件之一，其性能的好坏直接影响到船舶的正常营运和经济型，同时对防止尾轴滑油污染海洋环境起着十分重要的作用，因此国内外造船界和航运部门对其可靠性和可维修性等提出了更高的要求，所以对尾轴密封装置的研究是及其必要的。

下面笔者就对尾轴密封的发展及其展望做一个粗浅的分析。

第二章船舶尾轴密封的类型、原理及其发展2.1填料函型首密封装置“填料函型密封”俗称“盘根密封”，这种装置是最早出现的尾轴密封形式，多用于铁梨木尾轴承。

2.1.1填料函型首密封装置的工作原理图1为填料函型首密封装置的工作原理简图，此种密封装置主要是靠填料5来阻止舷外水流入机舱，填料5在压盖3的预紧力作用下与螺旋桨轴紧密接触，达到密封的目的。

尾轴承下沉时，可径向调节填料函本体4使与尾轴同心，以保持良好的密封效果。

该密封装置一般都设有进水管1，引入具有压力的舷外水，冷却和冲走积存在填料内的泥沙。

图1填料函型首密封装置的工作原理简图2.1.2填料函型首密封装置的特点填料函型首密封装置具有以下特点：（1）结构简单，易维护管理，当发现密封处漏水过多时，稍加压紧压盖即可；更换填料也很方便。

但由于盘根比较容易磨损，定时的对密封进行调整和填料（盘根）的更换，增加了轮机人员的劳动量，同时也增加了调整的随意性和不安全因素。

（2）造价低廉，使用可靠，现在该种密封装置一般都采用橡胶轴承。

相对来说橡胶轴承价格低廉，且使用可靠。