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 first of three blogs answering questions from our Supermarket Seminar Series: Metering Devices, TEVs.
Q: What if you can only mount the sensing bulb on a vertical suction line?
A: There are times when no other option is available. When one of those times happens, go ahead and install the bulb on the vertical suction line; however, this is a compromise. But how about installing an appropriate length of horizontal tubing at the evaporator outlet and before entering the trap for the riser? Now there is adequate room on a free-draining, horizontal length of tubing to install the bulb.
Q: If you must place the bulb on a vertical line, does it matter how it is oriented, tail up or tail down?
A: Keep in mind, the vertical line is not the preferred location; however, there are times when no other option is available. If the thermostatic charge is a liquid type, the position of the capillary tube makes little to no difference concerning the bulb. If it is the MOP style charge, it might make a difference. If that is the case, it would be best to install the bulb with the capillary tube pointing toward the sky or "tail up" as you have suggested. Then, route the capillary tube so that it is physically above the bulb location and even insulate it as a final precaution.
Q: Should the sensing bulbs or the thermistors, in the case of electrically actuated-electronically controlled expansion valves (EEVs), be insulated on the pipe?
A: Yes, insulating the bulb or thermistor is good practice. This helps reduce external influences on the bulb or thermistor. It also helps to manage condensation.
Q: Do we need to apply thermal mastic between the sensing bulb and the pipe?
A: If you follow Sporlan's recommended installation practices, thermal mastic should not be required.
Q: What is the max evaporator pressure drop before you need an external equalizer?
A: The pressure drop is rather small, in the range of 1 to 3 psid depending upon the refrigerant. Keep in mind, an externally equalized valve is necessary any time a refrigerant distributor is present in the system. One could substitute an externally equalized valve as a replacement for an internally equalized valve in just about any application. You simply need to install the equalizer line appropriately. The reciprocal is not true. If an externally equalized valve is required, an internally equalized version of the valve will not suffice.
Q: Why is the equalizing line connected downstream of the sensing bulb?
A: However unlikely, it is possible for an internal leak to develop in some thermostatic expansion valves (TEVs). In the event of a pushrod seal leak, refrigerant could be introduced into the low side of the system by way of the external equalizer line. This possible leak could influence the operation of the TEV by inadvertently cooling the sensing bulb and thus telling the valve to modulate to a more closed position. Positioning this connection downstream of the sensing bulb minimizes any interaction with the sensing bulb in the event an internal leak does occur in the TEV.
Q: Is the pressure tube typically connected after the distributor and before the coil?
A: If by "pressure tube," you mean the equalizer line, no, it must be installed and connected downstream of the evaporator. And better yet, it should be connected to the suction line downstream of the TEV sensing bulb. The distributor is on the inlet side of the evaporator between the TEV and the evaporator
Q: I've never seen an externally equalized valve with the second tube leaving the TEV. Are they uncommon?
A: No, externally equalized valves are not uncommon at all. In fact, most of the valves that Sporlan manufactures are externally equalized.
Q: Typically, I use an externally equalized valve for 4,000 BTU and up. Is that a correct approach?
A: It is a safe bet to utilize the externally equalized valve for almost any application. If the pressure drop across the evaporator coil is greater than 1 to 3 psid depending upon the system refrigerant, an externally equalized TEV is required. If there is a distributor in the system, an externally equalized valve is required.
Article contributed by Jim Jansen, senior application engineer, Sporlan Division of Parker Hannifin
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