This is A MUST KNOW about TXVs!

The Thermal Expansion Valve (TXV) will automatically control the flow of liquid refrigerant. This valve has been around for decades due to its simplicity of operation, making it a popular design option even during the twenty-first century. Not many operators/technicians would elect themselves to manually adjust a Hand Expansion Valve (HEV) every time a heat load change occurs.

TXV components include the powerhead, capillary tube, sensing bulb, and adjustment stem.

TXV Operation Fundamentals are the pressures that open & close the valve automatically. There are three (3) pressures:

• Sensing Bulb is the only pressure that opens the valve.
• Spring Pressure is trying to close the valve (adjustment stem is tuning this spring pressure).
• Evaporator Pressure is trying to close the valve (this pressure can be applied either internally or externally, industrial applications are most likely an externally equalized TXV due to the large pressure drop).

When purging/pumping out equipment with a TXV, it is best to verify ammonia refrigerant pressure has been evacuated from both sides of the TXV. When the pipe that the sensing bulb is "sensing" has no refrigerant present, the TXV should be in the open position. But as an operator/technician you must never ASSUME! A possible scenario to consider, is that the capillary tube/sensing bulb may have been damaged and lost its charge. Remember, the only pressure that opens the TXV is the pressure from the refrigerant inside the capillary tube/sensing bulb. This refrigerant is a separate charge from the rest of the system.

When replacing a TXV used for ammonia applications, keep in mind that the capillary tube is charged with ammonia "NH3". Make sure to wear the proper PPE if you do cut into the capillary tube for removal because there is an ammonia charge inside the capillary tube/sensing bulb. If this refrigerant charge is lost in an uncontrolled manner, it could expose you to high concentrations of ammonia.

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