As we introduced our Parker Sporlan webinar series we realized that we couldn't possibly answer all the questions in that short amount of time. We decided to create Climate Control blogs to answer some of the more pressing questions. This is the second of three blogs answering questions from our Supermarket Seminar Series: Metering Devices, TEVs.
Q: In my experience, balanced port valves can operate at a much lower pressure drop than a standard valve. Is this correct? And why do they work much better at a lower head pressure in the winter?
A: Balanced port valves are typically utilized to neutralize the opening force on a TEV that could be contributed by high side pressure. This comes into consideration with high-pressure refrigerants, like R-410A, and large capacity systems. The Balanced Port does allow the valve to modulate down to approximately 25% of rated valve capacity vs. 30% for a non-balanced or conventional valve. Customers have selected oversized balanced port valves for some applications. This selection technique contributes to the valve's ability to adequately function in winter conditions in the absence of head pressure controls.
Q: What applications require balanced port valves versus internally or externally equalized valves?
A: Balanced port valves are used in many applications ranging from small refrigeration units to large air conditioning systems. Please refer to the previous Question and Answer for more details regarding balanced port valves. Internally equalized valves sample evaporator pressure at the valve's outlet fitting and are suitable for use on systems with low-pressure drop across the evaporator coil. Externally equalized valves sample evaporator pressure at the installation point of the equalizer line. This is typically downstream from the sensing bulb of the Thermostatic Expansion Valve. An externally equalized valve is required if the pressure drop across the evaporator is high or a distributor is fitted in the system.
Q: Are balanced port valves available as either internally or externally equalized? And do they come in larger tonnage for HVAC?
A: Yes, balanced port valves are available as internally equalized and externally equalized versions. Balanced port valves are available in small, fractional tonnage capacities and are available up to 70 tons and more depending upon the refrigerant and the application.
Q: What is the part number of that superheat adjustment tool? This information would be handy for our technicians.
A: The superheat adjustment tool is only available through the Sporlan Store. Please contact your Sporlan Field Sales Engineer for assistance.
Q: Packing nut versus adjustment nut, is this the same item?
A: No, these two items are not the same. Some TEVs are manufactured with a packing nut. The packing nut is used to loosen or tighten the adjustment stem packing material around the adjustment stem. The adjusting stem is used to change the superheat setting of the TEV, and it may be accessed once the seal cap has been removed. If the TEV has a packing nut, it must first be loosened in order to allow the adjustment stem to be easily turned to set superheat. The packing nut must then be retightened to reduce leakage around the adjustment stem. Finally, the seal cap must be reinstalled as the final protective measure against leaks.
Q: Have you had issues with turning the adjustment too far and turning the disc to where it will not allow you to adjust the valve anymore?
A: It is possible to damage the adjustment mechanism on a TEV through abuse by using a wrench that is too large, etc. While this is not common, it can happen. If it does, either replace the valve or replace the adjustable bottom cap assembly.
Q: When is it recommended to use a ZP thermostatic charge?
A: Use the ZP thermostatic charge for low-temperature refrigeration systems, with evaporator temperatures ranging from 0ᵒF down to -40ᵒF, and when it is necessary to limit evaporator pressure during pulldown.
Q: What is the difference between Z and ZP thermostatic charge?
A: The Z and ZP thermostatic charges have the same low temperature operating range. Use both for evaporators with temperatures ranging from 0ᵒF down to -40ᵒF. However, the ZP has the maximum operating pressure feature built into the thermostatic charge and can limit evaporator pressure during pulldown. The Z thermostatic charge does not include this feature. The Z and ZP thermostatic charges are not intended as replacements, and each serves its own unique purpose.
Article contributed by Jim Jansen, senior application engineer, Sporlan Division of Parker Hannifin
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