Metering Devices: TEV Charts and Screens

 TXV Identification:

• Label Codes and Meanings:

  • S: Valve body style
  • V: Type of refrigerant
  • C: Indicates if the valve is color-coded for specific refrigerants

• Commercial Refrigeration TXVs:

  • Some valves can be used with multiple refrigerants if they have similar pressure-temperature relationships.
  • Example: A valve compatible with R502, R404a, R402a, and R507.

• Additional Information on Valve Labels:

  • F: Body style indicator
  • S: Refrigerant type (e.g., R404a)
  • E: Externally equalized
  • 1: Capacity (e.g., 1 ton or 12,000 BTUs)
  • Z: Low-temperature valve (for freezer applications)
  • P: Pressure-limiting or Maximum Operating Pressure (MOP) valve

System Effects on TXV Performance:

• High Pressure Drop: Increases the capacity of the TXV.
• High Liquid Temperature: Decreases the capacity of the TXV.
• Overall Impact: The effects of high pressure drop and high liquid temperature tend to offset each other, resulting in approximately 12% of the original capacity.

Correction Factor Table for Valve Capacities:

• High Pressure Drop: Correction factor of 1.40.
• High Liquid Temperature: Correction factor of 0.80.
• Net Correction Factor: 1.12 or 12% increase in capacity.

Valve Selection Charts:

• Selection Criteria:
  • Refrigerant type
  • Tonnage or capacity
  • Application (e.g., air conditioning, commercial freezer, ice machine)
• Valve Designations:
  • C: Medium temperature
  • Z: Low temperature (e.g., freezer applications)
  • ZP40: Low-temperature valve with a Maximum Operating Pressure (MOP) of 40 psig

Low-Temperature Valve Capacity:

• Nominal ratings may not apply in low-temperature applications.
• Example: A 3-ton valve may not provide sufficient capacity at a -20°F evaporator temperature and may only offer 2.1 tons. A 4-ton valve might be needed for proper operation.

TXV Screens:

• Location: On the inlet where the liquid line enters the valve.
• Function: To catch dirt, debris, and particulate matter.
• Serviceability:
  • Sweat Valves: Strainer is located at the top; some are removable for inspection and cleaning.
  • Flare Valves: Strainer is accessible at the inlet; can be removed and cleaned after pumping down or recovering the refrigerant.