Air Conditioners / Refrigeration

Having the Right Valves in the Van

August 20, 2012
Trans

Thermostatic expansion valves (TXVs) are critical components that control refrigerant flow in refrigeration and cooling system evaporator coils. HVACR contractors who replace TXV valves during servicing are always seeking ways to carry the variety of valves they need in their vans or trucks.

One new approach comes from Danfoss with its Maximizer and Minimizer kits, which package multiple TXV combinations in one place.

Time is money for commercial refrigeration and HVAC contractors like Eric Dorris, principal of EDCO Environmental Services in Crown Point, Ind. EDCO handles a wide range of customers, from restaurants and food stores to commercial buildings and residences. So when a service call comes in, EDCO service techs need to be prepared for any situation.

“We have a sizeable service area covering the northwest part of the state into Chicagoland,” said Dorris. “So it is really inconvenient if a service tech doesn’t have the proper TXV valve on the truck. He has to drive to the wholesaler to get the part and then drive back to install it. That takes time and gas that gets added to the customer’s bill without providing much value.”

To prevent run-arounds, Dorris makes sure each of his trucks has a Danfoss Maximizer Kit for refrigeration and a Minimizer Kit for air conditioning. “By packing multiple TXV combinations in one place, the kit saves us a lot of time. The tech always has the right valve on the truck, which gets our customers up and running fast and lets us service more customers in a day. And if the service call is in the middle of the night, it’s great to have a TXV valve handy to install then and there. The more customers we can make happy, the better it is for our business.”

According to Danfoss, its TXV valves are designed to maintain the optimal evaporator superheat regardless of changing conditions. “We use them on systems with high dynamic evaporators, such as air conditioning systems and refrigeration systems with plate heat exchangers that have high heat transfer rates,” Dorris said.

It was noted that the valves utilize a stainless steel power head that is integrated into the body, so there is one less leak point.

Dorris said that the TUA valves found in some of the refrigeration kits are easy to install. “These bimetal valves have a no-wrap feature. That means during brazing you don’t have the hassle of wrapping a damp rag around the power element and copper capillary tube to keep it cool. That’s because the bi-steel-copper design dissipates heat better than copper alone.”

Another aspect that Dorris favors is the superheating for each valve being set at the factory. Proper superheat temperature ensures the refrigerant leaving the evaporator has turned from liquid to gas before it reaches the compressor.

Dorris said the superheat setting of the TUA is good. “I don’t have to adjust superheat in practically 95 percent of applications. The valves are preset to about 9°F. The kit makes it easy to size the valve and the orifice correctly to ensure proper refrigerant flow into the evaporator. Superheat rarely needs to be adjusted.”

Danfoss produces several TXV kits. For a/c and heat pump applications, TR6 Minimizer kits are available for both R-410A and R-22 for systems ranging in capacity from 1½ to 6 tons, depending on the refrigerant. Each TR6 valve includes both flare and sweat fittings.

For refrigeration, Danfoss offers three additional kits. The Maximizer Kit includes six sweat and six flare valves, along with orifices ranging in capacity from 1/10 to 4½ tons for a total of 102 combinations. Minimizer Kits are also available with only sweat or flare valves. All refrigeration kits include valves for R-134a, R-22, and R-404, in both internally and externally equalized configurations.

It’s important to Dorris that his service techs have a combination that fits the application. A misapplied TXV valve can cause a number of problems. Oversized TXVs can cause the system to hunt between rising and falling superheat temperatures — a consequence of injecting too much refrigerant into the evaporator. A valve that is too small will not inject enough refrigerant, starving the coil and resulting in possible compressor overheating.

“About 80 percent of our applications are commercial and the rest are residential,” said Dorris. “We cover walk-in coolers and freezers, display cases, and ice machines all the way to rooftop packaged cooling systems to split systems. It’s great to have a TXV valve combination on the truck that’s right for all of these systems.” The valve components are stored in a fitted case that comes with a sizing and selection chart and an adjustment wrench. The component bins are numbered for replenishing the kit when technicians visit their stocking wholesaler; in the case of Dorris’ technicians, Johnstone Supply.

Because food refrigeration is a critical application, EDCO operates its service business 24 hours a day, 365 days a year.

And that, said Dorris, is a prime reason for the need to stock enough TXVs.

“We strive to have everything our customers need in stock at all times,” said Dorris. “We don’t want to be driving around to get parts while our customer’s dairy case is sweating. Our mission is to offer the quickest turnaround time in the industry.”

Publication date: 8/20/2012

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