through the servicing hose. This chemical drier is provided to remove any moisture in the oxygen supply. The oxygen flows into the bottom of the drier, passes up through the drying agent, and out through the servicing hose. SERVICING  HOSE  AND  LINE  VALVE. The servicing hose is a high-pressure, nonkinking, metallic flexible hose. The line servicing valve is attached  to  the  servicing  hose  and  is  used  to control the flow of oxygen to the system being charged. OPERATION The  six  supply  cylinders  are  connected  by means   of   flexible   hoses   to   their   respective control valves (fig. 5-14). The six control valves are attached to the upper manifold. A pressure gauge is screwed into each control valve at a point below the seat. This allows each cylinder pressure to be easily read. The oxygen flows from the upper manifold through either of two pressure regulators via two shutoff  valves. The oxygen is collected in the lower manifold where a gauge registers the pressure of the delivery side  of  the  system.  The  lower  manifold  is connected by flexible hose to a drier, which filters and dries the oxygen. The servicing hose connects directly to the drier and has a line servicing valve on the terminal end. The line servicing valve is fitted with a standard oxygen cylinder connection. Loading Cylinders The servicing trailer is capable of having its cylinders recharged without removal. However, many  operating  activities  replace  the  empty cylinders  with  full  cylinders. NOTE: NEVER completely expend the supply of oxygen from a cylinder. Always leave a residual pressure in excess of 50 psi. REMOVAL  OF  EMPTY  CYLINDERS.— When  the  trailer  has  been  in  use  and  cylinder pressure  is  low,  the  cylinders  are  removed  as described  below. 1. Close all lever valves on the manifold prior to removing any cylinders. 2. Close the cylinder shutoff valves. 3.  Disconnect  the  flexible  hose  that  connects the cylinder to the manifold. 4. 5. 6. Loosen  the  clamping  arrangement  that holds the cylinders to the trailer. Install the cylinder safety caps. Remove  the  empty  cylinders. CAUTION Do not attempt to remove empty cylinders while  charging. INSTALLATION  OF  FULL  CYLIN- DERS.—  The  trailer  should  be  loaded  with cylinders while fastened to a towing vehicle. If a towing  vehicle  is  not  available,  the  rear  stand should be let down and hand brakes applied so the weight of the cylinders will not cause the trailer to tilt backwards. The retractable swivel wheel should be down if the trailer is not hooked to a towing vehicle. (When the trailer is hooked to the towing  vehicle,  the  swivel  wheel  should  be retracted.) Cylinders should be loaded from the rear and should be handled with safety caps in place. Standing cylinders should be brought to within 4 feet of the rear end of the trailer. If the cylinders are lying down, the safety cap end of the cylinder should be just below the rear of the trailer. The safety cap end of the cylinder should be lifted or lowered and placed in the appropriate channel. The bottom of the cylinder should be raised and the cylinder worked into place. Ensure that the cylinder is in its forward-most position and firmly seated against the forward cylinder stop. Remove the cylinder safety cap. Position the cylinder so that the cylinder valve outlet may be easily connected to the flexible hose without causing undue strain on the hose. Prior to connecting the hose to the cylinder, open the cylinder.  valve  slightly  to  blow  any  foreign matter from the outlet of the valve; then close the valve. Connect the flexible hose nut to the power cylinder valve. As soon as the cylinders are in place  and  the  hoses  connected,  the  clamping arrangement should be tightened. The bottom four cylinders are clamped in pairs by a wheel, and the top cylinders are tightened by a single strap for each one. After  tightening  the  coupling  nuts  on  the hoses, the hoses should be free of twisting strain. This strain can be prevented by gripping the hose with one hand and twisting slightly in a clockwise direction while tightening the coupling nut. When the  nut  becomes  tight,  the  hose  will  twist (counterclockwise) slightly as it seats, and will stop approximately at its neutral position. 5-18