Thermal Expansion Valves - Why The Spiral?

So I know the general function of a TXV, but why does the capillary tube have to be spiraled like that?

It reminds me of the coil from a copper still, but that doesn’t seem to have a similar purpose.

What happens in the spiral?

“A TXV type expansion device has a sensing bulb that’s filled with a liquid whose thermodynamic properties are similar to those of the refrigerant. This bulb is thermally connected to the output of the evaporator so that the temperature of the refrigerant that leaves the evaporator can be sensed. The gas pressure in the sensing bulb provides the force to open the TXV, therefore dynamically adjusting the flow of refrigerant inside the evaporator and, as a result, the superheat that’s acquired by the refrigerant that exits the evaporator.[[1]]”(Thermal expansion valve - Wikipedia)
The picture you posted shows a TXV as it is packaged. During installation the capillary tube is unwound so that the sensing bulb can be inserted in the evaporator fins.


Ah ha, thank you sir! That was my hunch, but I commonly see them installed and still spiraled up so I wasn’t sure.