the expansion valve/regulator is a more complex piec of equiment which meter the flow of refrigerant from the high-pressure to the low pree side of te system.
this may be of the thermostatic type,as show in 9.8
the bulb senses the temperature of the refrigerant at the outlet from the evaporator and open or closes the valve accordingly.
the design of the valve is critical and is related to the pressure difference between the delivery and expansion sid.
there fore it is essential that the delivery pressure is maintained at or near the maximum design pressure.
thus if the vessel is operating in cold sea water temperatures it is necessary to re-circulate the cooling water to maintain the correct delivery pressure from the condenser.
if this is not done, the valve will hunt and refrigerant liquid may be returned to the compressor suction