Metering Devices: Balanced Port TEV

 Balanced Port TXVs Overview:

• Purpose: Balanced port TXVs are used in commercial refrigeration and heat pump applications.
• Functionality: They are designed to handle varying inlet pressures that occur due to large swings in outdoor ambient temperature, which directly affect the liquid line pressure entering the valve. This variability can cause a standard TXV to overfeed or underfeed the evaporator.
• Operation: Balanced port TXVs balance the bulb pressure with the inlet pressure, providing more consistent operation and metering. This prevents underfeeding during low liquid line pressures and overfeeding during high liquid line conditions.

Comparison of Standard and Balanced Port TXVs:

• Standard TXVs:

  • Low Ambient Conditions: Reduced liquid line pressure can cause the valve to starve the evaporator slightly.
  • High Ambient Conditions: Increased liquid line pressure can cause the valve to overfeed the evaporator, leading to flooding.

• Balanced Port TXVs:

  • In both low and high ambient conditions, the balanced port design applies liquid line pressure equally as an opening and closing force. This cancels out the effects of liquid line pressure fluctuations, ensuring the valve feeds the evaporator properly.

Balanced Port TXV Selection:

• Capacity Designation: The capacity of a balanced port TXV is designated by a letter (not a number), and tonnage is given as a range of capacities. One valve size can cover a broad range of BTU capacities.
• Example of Selection Chart:
  • B: Indicates a balanced port valve.
  • F: Valve body style (e.g., flare connection).
  • VI: Refrigerant type.
  • E: Externally equalized valve.
  • Port Size: Designated by letters (e.g., AAA or DA), governing the valve's capacity or tonnage range (e.g., 1/8 ton through 1/3 ton).

Thermostatic Bulb Charges:

• Balanced port TXVs are available with different thermostatic bulb charges depending on the application:
  • CA: Commercial medium temperature valve.
  • Z: Low temperature valve (freezer application).
  • ZP 40: Maximum operating pressure valve that limits evaporator pressure to 40 psig.

Summary:

• B: Balanced port valve.
• F: Valve body type (e.g., flare).
• V: Refrigerant type (e.g., R22).
• E: Externally equalized valve.
• Letter Designation (e.g., AAA): Port size and capacity range.