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.