line  or  coil  and  is  drawn  back  into  the  compressor intermittently in slugs, there is danger of injury to the moving  parts  of  the  compressor. I n    g e n e r a l , t h e    e x p a n s i o n    v a l v e s    f o r air-conditioning a n d    w a t e r - c o o l i n g    p l a n t s (high-temperature  installations)  normally  are  adjusted for higher superheat than the expansion valves for cold storage  refrigeration  and  ship’s  service  store  equipment (low-temperature installations). You may not be able to adjust expansion valves to the  desired  settings,  or  you  may  suspect  that  the expansion  valve  assembly  is  defective  and  requires replacement.  In  either  case,  you  should  make appropriate tests. First you should be sure that the liquid strainers   are   clean,   that   the   solenoid   valves   are operative,  and  that  the  system  is  sufficiently  charged with  refrigerant. The  major  pieces  of  equipment  required  for expansion valve tests is as follows: l   A service drum of R-12 or a supply of clean, dry air at 70 to 100 psig. The service drum is used to supply gas under pressure. The gas does not have to be the same as that used in the thermal element of the valve being tested. l  A  high-pressure  and  a  low-pressure  gauge.  The low-pressure  gauge  should  be  accurate  and  in good condition so that the pointer does not have any appreciable lost motion. The high-pressure gauge,  while  not  absolutely  necessary,  will  be useful in showing the pressure on the inlet side of  the  valve.  Refrigeration  plants  are  provided with  suitable  replacement  and  test  pressure gauges. The procedure for testing is as follows: 1. Connect the valve inlet to the gas supply with the  high-pressure  gauge  attached  to  indicate  the  gas pressure to the valve. Connect the low-pressure gauge loosely  to  the  expansion  valve  outlet.  The  reason  the low-pressure gauge is connected loosely is to allow a small amount of leakage through the connection. 2.   Insert the expansion valve thermal element in a bath of crushed ice. Do NOT attempt to perform this test with a container full of water in which a small amount of crushed ice is floating. 3.   Open the valve on either the service drum or in the air supply line. Make certain that the gas supply is sufficient to build up the pressure to at least 70 psi on the  high-pressure  gauge  connected  in  the  line  to  the valve inlet. 4.   The expansion valve can now be adjusted. If you want to adjust for 10°F superheat, the pressure on the outlet gauge should be 22.5 psig. This is equivalent to an R-12 evaporating temperature of 22°F. Since the ice maintains the bulb at 32°F. the valve adjustment is for 10°F superheat (difference between 32 and 22). For a 5°F superheat adjustment, the valve should be adjusted to  give  a  pressure  of  approximately  26.1  psig.  There must   be   a   small   amount   of   leakage   through   the low-pressure  gauge  connection  while  this  adjustment  is being  made. 5.   To determine if the valve operates smoothly, tap the  valve  body  lightly  with  a  small  weight.  The low-pressure gauge needle should not jump more than 1 psi. 6.   Now  tighten  the  low-pressure  gauge  connection to  stop  the  leakage  at  the  joint  and  determine  if  the expansion  valve  seats  tightly.  If  the  valve  is  in  good condition, the pressure will increase a few pounds and then  either  stop  or  build  up  very  slowly.  But  with  a leaking valve, the pressure will build up rapidly until it equals  the  inlet  pressure.  With  externally  equalized valves,  the  equalizer  line  must  be  connected  to  the piping from the valve outlet to the test gauge to obtain an accurate superheat setting. 7.   Again loosen the gauge to permit leakage at the gauge  connection.  Remove  the  thermal  element,  or control bulb, from the crushed ice. Warm it with your hands or place it in water that is at room temperature. When this is done, the pressure should increase rapidly, showing that the power element has not lost its charge. If there is no increase in pressure, the power element is dead. 8.  With  high  pressure  readings  showing  on  both gauges, the valve can be tested to determine if the body joints or the bellows leak This can be done by using a halide leak detector. When you perform this test, it is important that the body of the valve have a fairly high pressure applied to it. In addition, the gauges and other fittings  should  be  made  up  tightly  at  the  joints  to eliminate  leakage  at  these  points. Replacement  of  Valves If  the  expansion  valve  is  defective,  it  must  be replaced.  Most  valves  used  on  naval  ships  have replaceable  assemblies.  Sometimes  it  is  possible  to replace a faulty power element or some other part of the 5-8