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故障现象 机组反应30分钟内左油箱油量比右油箱多140公斤。 排故思路 可能是交输活门关不严或者翼梁活门管路或封圈漏油。 记录左右油箱当前油量 。 1. 针对交输活门 交输活门关，放油活门开，1号油箱加油活门开，2号油箱油泵开，保持15分钟，检查左油箱是否油量有增加，有则说明交输活门关不 严。 2. 针对翼梁活门上游问题 打开2号油箱燃油泵，打开交输活门，保持15分钟，检查左油箱是否油量有增加。 3. 针对翼梁活门下游问题 打开2号油箱燃油泵，打开交输活门，打开左发翼梁活门，保持15分钟，检查左油箱是否油量有增加。 问题 针对1：按照1的操作，这不是手册中右主油箱向左主油箱倒油吗？左主油箱油量理应增加啊？ 针对2，3都不大理解。 希望大拿们一起分析分析。 先来看看油箱正常串油的原理  这是我之前画的一张原理图，点击图片查看大图。红色为燃油供油，蓝色为加油和抽油，箭头代表单向活门。 串油的基本原理： 油从红色走到蓝色：即油箱中的油先经过抽油活门到加油站，再通过油箱的加油活门进入对应油箱！ 油箱之间串油首先抽油活门和要串入油箱的加油活门肯定要打开，剩下就是泵的开关和交输活门的开关。 交输活门将燃油系统分成了左右部分，而加油站在交输活门右边。所以从右主油箱往左主油箱倒油，是不用经过交输活门的，也就是说交输活门打开与否都行。也就是说针对1的方案是错误的。 再比如，从中央油箱往左油箱串油，有两种方法： 方法一，关闭左油箱前后泵，打开交输活门和中央油箱左泵，打开抽油活门和左油箱加油活门。 方法二，关闭左油箱前后泵，打开中央油箱右泵，打开抽油活门和左油箱加油活门，不用打开交输活门。 类似的故障我们也遇到过： 最后确定是交输活门的原因 按AMM调节了一下，好了 最终趁C检更换掉了 下面分享我的排故思路 排故思路 比较双发燃油流量 译码或者询问机组都能得到发动机燃油流量，对比看看有没有大的差别，来判断是否是发动机性能上的差异。 比较发动机和油箱燃油消耗量 飞机上的燃油流量开关除了正常的看发动机燃油流量外，搬到USED位还能看到发动机已经消耗的燃油量。 对比发动机所消耗的油量和燃油箱所消耗的油量，来判断是否有外漏。 排除发动机和漏油原因后，就只能是燃油供油系统内漏或指示故障。 注意这里的内漏并不是说左右主油箱在串油，因为抽油活门和加油活门同时未关闭故障的可能性很低。 正常交输活门关闭，中央油箱泵关闭情况下，左发用左油箱的油，右发用右油箱的油。（如果中央油箱两个泵都打开，双发都用中央油箱的油） 原因分析 以本案例来说，左油箱消耗大，这里的内漏指的是本来左主油箱只给左发供油，但却同时又给右发供油了。（前面原理图中的红色部分） 而发生这一结果的唯一可能就是交输活门在关闭位未能关严，左、右主油箱的泵的压力又刚好会有轻微，发动机供油就会串油。 交输活门内漏判断方法 其实在AMM手册里就有： TASK 28-22-00-730-802 Crossfeed Valve - Functional Test
 故障处理 交输活门内漏 交输活门的指示位置在主轮舱就能到，特别值得注意的是，这里的位置是活门作动器的位置，活门本体在燃油总管上，我们无法看到。 活门作动器在关位，但是活门没关严，导致了内漏。通常是由于活门本体上作动活门的轴的花键磨损造成的。
而更换作动器无法解决问题。 737-SL-28-073-C Worn Splines (Crossfeed valve position) Boeing received several reports of fuel imbalance during flight on 737NG airplanes. Theseairplanes had accumulated between 22,928 and 27,390 hours when imbalance was reported. Thecrew was able to correct the imbalance using existing procedures. Subsequent troubleshootingidentified that the imbalance was caused by a leaking crossfeed valve. Boeing and ITT investigated the removed valves and concluded the wear was caused bymechanical contact between the aluminum disk and the CRES shaft caused by the fact that thespline end of the disk is supported by the spline alone. Valve body assy. P/N S343T003-67 (ITTP/N 125334D-2) has a bearing added to the spline end of the disk. This bearing supports the diskload and the spline transmits only torque to the disk to open and close the valve. Boeing has checked the free play in the valve system on several 737NG and 757 aircraft withmultiple operators, and reviewed all prior reports of fuel imbalances and engine shutdownevents. The accelerated wear in the spline is isolated to the 737NG crossfeed valve. Boeing has determined that this wear does not represent a safety issue, as the condition isindicated to the crew as a fuel imbalance before the valve performance degrades to the point thatthe crossfeed valve cannot be opened when required. SUGGESTED OPERATOR ACTION Since the crossfeed valve worn spline issue was found to not be a safety issue, Boeing leaves itto the operators to determine the action they would like to adopt. Some possible actions thatcould be taken are listed below: 1) Operators could decide to replace the crossfeed valve when the spar valve is changed per thereference SB737-28-1272. 2) Operators could decide to replace the crossfeed valve during a heavy check when the airplanehas accumulated approximately 20,000 hours. 3) Operators could decide to inspect the crossfeed valve wear using the procedure provided inthe attachment to this service letter, starting at 20,000 hours. This inspection could be repeatedat convenient maintenance intervals until the wear has progressed to 16-18 degrees at which timethe valve should be scheduled for replacement. The initial repeat inspection interval could bedetermined based on the operator’s maintenance program and reports of worn crossfeed valvesplines. The inspection interval could be adjusted based on wear observed during the periodicinspections. 4) Operators could decide to wait until an imbalance is reported by the flight crew. Uponconfirmation that the imbalance was caused by crossfeed valve spline wear, the crossfeed valvewould need to be replaced prior to next flight. 交输活门校准 由于活门更换起来不是很容易，建议先校准，后续安排停场时间更换。AMM手册有校准程序： TASK 28-22-21-820-801 Crossfeed Valve Alignment 校准程序也很简单 只是需要一个专用工具：B28009-1 当然对一些使用时间较长的旧活门 个人建议还是安排C检更换比较好 最后需要提醒的是 如果是燃油箱串油故障时，除了交输活门外，还得考虑油箱内部管接头漏油。由于左右主油箱增压泵及泵的吸油管都在中央油箱里，所以如果这些管接头漏油会造成主油箱油量减少而中央油箱油量增加，这样的故障在737NG飞机上也已经发生过多次了。
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磨损的花键
