An externally equalized TXV is required whenever the pressure drop in the evaporator exceeds 3 psig (a/c applications); 2 psig (commercial refrigeration applications); or 1 psig (low-temp applications).

What is the purpose of an external equalizer on a TXV?

The purpose of the external equalizer is to sense the pressure in the suction line at the bulb location and transmit it to the TEV diaphragm. This usually means installing the external equalizer immediately downstream from the bulb. This ensures the correct pressure is signaled to the TEV.

What is the difference between an internally and externally equalized TXV?

An internally equalized TXV uses evaporator inlet pressure to create the 'closing' force on the valve. An externally equalized valve uses the evaporator outlet pressure, thereby compensating for any pressure drop through the evaporator. ... The only way this can be accomplished is through the use of a 'bleed' type TXV.