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SAMPLE TAKING
Description - 14020_179

Aviation Structural Mechanic E2 - How airplanes are built and how to maintain them
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inch in diameter, attached directly to the tank drain outlet, or trailer fill-drain outlet, is recommended by current directives. All flare fittings must be perfect—without dents, scratches, or toolmarks. Do not use any antiseize compound on threads or any cleaning compounds on sampler parts. Contamination will result. A sampler received without residual pressure probably leaks. Such samplers should be rejected and returned. Just before sampling, remove the cap from the sampler valve; open the valve to release shipping gas pressure, then reclose. Next, remove the valve by disconnecting the adapter from the nipple, and place the cylinder upright in a holder. Attach the separator and line assembly to the tank drain or fill-drain outlet. Using a trailer pressure of 10 to 20 psi, let the LOX flow into an open container, such as the receiving vessel shown in figure 5-10, for at least 30 seconds to purge the line. Adjust the pressure to obtain a quiet, uniform, full flow from the separator outlet tube. Wipe the frost from the separator outlet tube, and immediately insert the outlet into the sampler tube and fill it. The filling will take approximately 1 minute. When liquid splashes in droplets over the top, the tube assembly is full. The sampling tube holds about 180 milliliters (6. 12 oz) of LOX, which produces a maximum pressure of 300 psi when vaporized in the closed sampler. NOTE: During the filling operation, the operator should wear a face shield, hat, gloves, and other protective equipment as excessive pressure will violently throw LOX from the tube assembly. As soon as the sampler tube is filled, remove the separator from the sampler assembly and install the adapter to the cylinder. Close it tightly with end wrenches, making sure that the valve is fully closed. Turn sampler upside down for a few minutes to allow liquid to flow from the sampler tube into the cylinder. Immerse the valve of the cylinder in water to check for leaks. PURGING Purging and other maintenance of LOX trailers is performed by the AS rating. Purging is the cleansing of impurities from oxygen systems and containers. There are two ways to purge oxygen containers, LOX wash and gas purging. 5-14 The LOX wash method is used on large containers, such as storage tanks and LOX trailers, to lower the contamination to acceptable levels by replacing the contaminated LOX with LOX known to be uncontaminated. To do this, drain the container using the buildup coil. Do NOT open the vent during this operation. Partially fill the container with un- contaminated LOX and allow the container to stabilize. Build up pressure to 30 to 40 psi and then vent the pressure to 0 psi. Repeat this opera- tion for a total of three cycles. Take a sample and forward it to a designated site for analysis. If the sample is acceptable, the container may be put into service. If the sample is not acceptable, the container must be gas purged using hot water pumped nitrogen. If allowed to run dry or if odor is detected in the system, aircraft LOX converters must be gas purged before being put into service. Gas purg- ing of aircraft LOX systems must be done if any maintenance is performed on the system that opens it to the atmosphere. To gas purge a LOX converter, first drain the converter of LOX. If possible, allow the converter to warm to ambient temperature. This saves vast amounts of nitrogen. Attach a purging device to Figure 5-11.—Purging unit ready for use.







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