the thermostatic assembly is inoperable. Corrective maintenance   of   the   regulating   valve   consists   of inspecting the valve for leaks and for freedom of stem movement,  adjusting  the  set  point  at  which  the  valve regulates, renewing the thermostatic assembly, and cleaning and restoring valve parts. Any time that you remove a valve, you should center punch a dot code on each piece to ensure that the valve and piping are installed  in  the  original  configuration.  The  three-way valve can be turned around, and the problem could go unnoticed  until  you  try  to  align  the  temperature regulation  of  the  cooling  system.  There  are  individual manuals for the temperature-regulating valves and they should be closely followed. For example, if you remove the top of the thermostatic assembly without chilling the temperature probe, the bellows will expand and rupture, making  the  unit  worthless.  To  verify  that  the thermostatic  assembly  has  failed,  close  valves  upstream and downstream of the thermostatic bulb, drain the unit below the location of the bulb, and remove the bulb from its well. Place the bulb in a suitable vessel and observe the valve stroke while the bulb is alternately heated with hot  water  and  cooled  with  cold  water.  If  the  valve thermostatic assembly does not respond, it has lost its thermostatic charge, and a new unit must be installed. FLOW  REGULATORS You will encounter many different types and sizes of flow regulating devices used in both the primary and secondary  cooling  systems.  They  are  used  to  reduce  the pressure or the flow of coolant through a cooling system. The orifice plate is found primarily in the seawater cooling system. It is the simplest design of a flow regulating device, consisting of a steel plate with a hole in it. With constant known seawater pressure and with a given hole size, the volume of water through the device can be determined. The use of an orifice plate is limited to where the input water pressure is essential y constant, such as the ship’s firemain. The orifice plate is normally installed  between  two  pieces  of  flanged  pipes  upstream from the heat exchanger as shown in figures 1-6 and 1-7. This will reduce the ship’s firemain pressure below the pressure  in  the  secondary  cooling  system.  As  we  have indicated earlier, should one of the heat exchanger tubes fail,  the  seawater  pressure  is  lower  than  the  distilled water  pressure;  therefore,  it  would  not  contaminate  the secondary  cooling  system.  The  secondary  cooling system would force distilled water into the primary cooling system. A ruptured heat exchanger tube or a bad single tube sheet in a heat exchanger would give no visual indication of water loss except for the indication on the expansion tank sight glass. To stabilize the flow of  seawater  and  to  prevent  jet  erosion  of  the  heat exchanger and associated piping, the orifice plate should be installed with at least 15 pipe diameters of straight pipe upstream from the heat exchanger. When there is a drop in the heat exchanger primary input pressure and the seawater supply pressure has not changed, you should  first  check  the  duplex  strainer  differential pressure gauge to ensure that the duplex strainer is clean. Then the orifice plate should be inspected for deposits or  particles  that  could  restrict  the  seawater  flow.  You should  also  inspect  the  orifice  plate  for  erosion  damage of  the  hole  diameter. The  orifice  plate  should  be replaced when there is an increased flow of seawater to the point that it could damage the heat exchanger. Never use the seawater valves to throttle (partially closed) the flow of seawater in the primary cooling system, because the seawater will erode the internal parts of the valve. The damage to the valve would require extensive repair or replacement, because the valve would no longer close properly. When  used  with  the  chilled-water  system,  the constant flow regulator (variable orifice, fig. 1-17) is installed downstream from the heat exchanger. This restricts the flow from the heat exchanger and keeps the heat  exchanger  fully  submerged  for  greater  efficiency (heat transfer). This type of flow regulator is not used in the seawater system because the internal parts would easily become fouled with marine growth and deposits. The operation is dependent on the movement of the orifice plugs (neoprene) to regulate the flow of water. Another type of flow-regulator valve (equipment flow)  used  primarily  with  electronic  equipment  to regulate  the  flow  of  distilled  water  through  the Figure 1-17.-Constant flow regulator. 1-15