The thermostaic expansion valve (TXV) is one of the four major components of any RSW system. Its function is to meter refrigerant into the evaporator or coils. In the correct amount... The basic valve consists of an inlet, outlet, bellows and a super heat adjustment. Stem. It works this way. Cool liquid refrigerant enters the valve through a needle port. The needle is mounted on one end of a hollow cadge with a spring inserted in it.. This spring buts up on the other end to a plate with an adjustment screw on the other side. It mounts in the valve with external leak proof cap. This is the superheat adjustment stem. The bellows is filled with the same refrigerant used in the system. With system off for some time the tempiture and pressures in the bellows and the valve are equal. When the compressor is started it reduces the pressure in the valve and the bellows with its higher pressure pushes on two tiny push rods through the valve onto the outside edge of the cadge that forces the needle valve open. Refrigerant starts flowing through the valve into the evaporator (coils). The bellows bulb is firmly attaché to the out let of the evaporator (coils) once the raw refrigerant reaches the bulb it decreases the pressure in the bellows and the valve stars to close via the spring pressure on the cadge.
Getting the correct superheat setting is very important, best covered in the next post
Troubleshooting, repair, and how-to's related to marine systems.
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