Industrial Refrigeration Control Valve Lightens Up

October 28, 2004
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Industrial refrigeration technicians face a four-horned challenge when it comes to control valves. First, traditional beefed-up industrial valves are big. And the darn things can be downright heavy since they are typically made of cast iron.

Then, the way they are put together - with flanged connections and a service port on the bottom - results in a leak potential that anybody would avoid if they could. And just like every other sector of HVACR, industrial refrigeration has a refrigerant situation that is constantly in a state of flux.

What if a manufacturer could come up with a new valve that is comparatively lightweight, reduces leak potential to a minimum with only one gasket instead of four, and is able to work with a range of refrigerants, from HFCs to ammonia to CO2?

Danfoss has announced it is offering a new valve that promises to achieve all of these goals, plus the company says the valve is easier to install and service. Its industrial control valve platform (ICV) is based on a modular concept that includes both mechanical pilot operated (ICS) and digitally actuated (ICM) configurations using the same valve body. According to Danfoss, ICV valves have a 750-psi working pressure, direct weld connections, optimized flow geometry, and reduced size and weight.

Reducing Valve Weight, Dealing With Leaks

Brian Davis, vice president of Industrial Refrigeration at the Danfoss Air Conditioning & Refrigeration Division in Baltimore, told The News that by building the ICV valve from steel, Danfoss was able to reduce the industrial valve's weight by two-thirds.

Niels Vestergaard of Danfoss' Business Research Department said that tolerance for leaks is lower than ever before, regardless of the refrigerant used. He said that industrial refrigeration system owners have to prove that their systems are tight.

"We wanted to remove as much as possible the risk of leakage and that is what we have done," he said. "Instead of four possible places for leaks on each valve, with the ICV there is now just one."

The modular ICV design has three parts: the valve body, a function module, and a top cover. All of the valve's refrigerant-handling functionality is built into a unitary changeable module. All service is accomplished by removing the top cover and changing function modules.

Vestergaard said a great deal of research went into making the ICV concept a reality. "We put a group together, with people from all regions of the world, and asked them to help us design control valves for the future.

"Then we took that input and came up with something that is vastly different from what people had been used to for the past 30 years. We knew we had to make an argument that was going to be able to stand and be convincing enough that users would say, ‘Yes, this is a different direction, and clearly a better direction.' They would appreciate that ICV is a generation ahead."

Servo and magnetically coupled digital motorized valves are lightweight and compact, less likely to leak, and service friendly, according to the company. The industrial control valve platform (ICV) is based on a modular concept that includes both mechanical pilot operated (ICS) and digitally actuated (ICM) configurations on the same valve body. The ICM is shown above, and the ICS version is shown below.

Flexibility, Modularity

Davis explained, "We looked at the mechanical or servo control valve that typically serves as a pressure regulating valve or solenoid valve. Then we considered a motorized valve as being a second side of the offering.

"Although we are changing the foundation of the mechanical valve, its housing, our pilots - those devices we screw into the top cover that define the functionality of the valve - are the same time-tested and proven ones that we have supplied for years. There is no reason to change them except to be able to address a 750-psi requirement for CO2. But most of the other pilots are perfectly the same as they have been.

"On the motorized side, we have a program that still functions with the same black boxes, the controllers that we've been using on the existing product line with maybe some minor software changes. So we didn't change the interface there either. But we did make changes.

"If you look at the Danfoss valve itself, you see that it is similar to the existing program in that there is a top cover designed for single function, or a top cover designed for three functions. But what you notice right away is that it is a direct weld body, not a flanged body.

"And being direct weld, it allowed Danfoss to change to low temperature steel. That change, in turn, makes possible a much higher design working pressure and allows a substantial reduction in the valve's weight and size.

"Our motorized valve is an open motor design. The motor is removable from the valve housing. Generally speaking, if there is going to be a problem with a motorized valve, it is likely to be in the motor, maybe a motor burnout. So our design philosophy is that we want to be able to separate the motor from the valve housing."

Vestergaard noted that Danfoss looked at a new design to see how to maintain the philosophy of an open motor and improve on it by eliminating a wearable seal. This was accomplished through the use of a magnetic coupling. "With the new valve, you get a visual indication of the valve position, something you can't have if the valve is hermetically sealed to the motor," he said.

Vestergaard looked at the concept as a road map for the future. "When we start to look at the world of the future as having more and more electronics, there is a tendency to ask, ‘Why not just come out with an electronic valve?' In principle, you can take the ICV and make whatever you like. It is just a question of putting a new program into the controller.

"On the other hand, there are simple refrigeration systems where you do not need electronics. Why should we then introduce electronics? That is when we realized what the market really needed, and it's why we have both the servo and motorized versions on the same platform."

Higher Pressures

Davis said, "We have seen the pressure requirements for control valves increasing, and we have been able to upgrade our (cast iron) products to a higher pressure rating, but we have reached the material's practical limit.

"One challenge with large-scale or industrial refrigeration systems is that you can experience liquid hammering that subjects a valve to huge impacts. Casting steel is more complex and that requires another technique. So we use an advanced type of casting. It's more difficult to manufacture with low-temperature steel than with gray cast iron, but we were able to find a solution where we end up with a stronger valve housing."

Both Danfoss officials said the new line of valves will be competitively priced with other valves currently on the market.

The Refrigerant Issue

"As our industry is continually faced with changing refrigerant regulations, and looks at alternative refrigerants," Vestergaard said, "Danfoss continues to pioneer solutions," including those in response to the growing interest in CO2.

"In Europe," he said, "CO2 is a growing market, so we had to meet its higher pressure requirements when designing the ICV."

The valve's pressure rating is 750 psi, but another thing is that the differential pressure this valve has to work with. For hot gas defrost, differential pressure can be 450 psi, and that is a tough one for a control valve. A differential that big requires special design considerations and that is why we have a piston and also a special V-cone for regulation, to meet those high demands. So we have a single valve platform, which is universal for ammonia, CO2, and R-410A."

Ease Of Use

Davis touched on the use of a welded instead of a flanged body.

"The biggest reason for the flanged body is what's inside the pilot-operated solenoid valve. There are a whole lot of parts. There are pistons, seats, springs, retainer clips, etc.

"So what happens when technicians are trying to troubleshoot and fix the valve is that, more often than not, they'll take the bolts off both sides, remove the valve, put it on the bench, take it apart and rebuild it. And before they do that, they have to know in advance what repair kit they need.

"So if we are going to have a welded configuration, then we have to make it extremely easy to service in place, without re-moving it from the system. Consequently, what we have is a three-piece design: a top cover that is either single pilot or three pilot and a function module; a single piece that contains the only wear item in the valve; and a housing.

"This housing is the same whether you are using it for the mechanical valve or for the motorized valve. So the platform has a common housing, one of two function modules - motorized or mechanical - and the top cover. If there is any question as to whether the valve is functioning properly or not, the tech simply removes four bolts, takes off the top cover, and changes out the function module.

"When you replace the single-piece function module, you have completely renewed and rebuilt the valve, because there are no wear surfaces inside the housing. The seat itself is inside the function module.

"One of the things we have done for the piston in the function module is to recognize that it has to be robust. It has to be resilient. So it has been designed with a piston ring that is spring loaded. The piston ring will expand as its Teflon wears, and so it maintains a tight seal against the inside of the cylinder wall.

"We also have V-ports inside the seat, so we are able to control over a much broader pressure range, and control, even at low capacities, is better than we can accomplish with current technology. The ICV is designed for a wide range of temperatures, pressures, and flows.

Vestergaard looked at the ICV concept as "a modular system where we have designed a universal valve housing. But the housing itself cannot do anything. So in adding functionality to the valve, you select different function modules, which give different capacities, in either pilot-operated or digital motorized version. So it is a modular system where you can combine in anyway and shift around if you like."

In the motorized version, Davis noted, "The motor drives the valve with a magnetic coupling. We have a three-piece design with a function module that encompasses the bonnet itself. We have a magnet inside that rotates and opens and closes the valve. Rotary motion is translated into linear motion. The motor sits protected on top and is sealed. The valve housing is also sealed, and there's a magnetic coupling - the outer magnet turning the inner magnet to modulate the valve.

"The advantage is that you have an open motor that gives you the flexibility to have complete programmability right on top of the motor housing."

The modular valve design is comprised of three elements: a valve body, a function module, and a top cover. The industrial control valve platform (ICV) is available in both servo (ICS) and magnetically coupled digital motorized (ICM) versions.

Programming

"The motor is a digital stepper motor, and you need a driver to control it," Vestergaard stated. "We built that in. It is not just a driver, but an intelligent driver that gives the valve great flexibility of function."

Davis commented, "When we look at current designs for motorized valves, they move at only one speed, and so the valves are perfectly alright for liquid makeup and they're OK as suction pressure regulators. But for dry expansion, where you have to have very good reactivity, or for liquid injection in a screw compressor where you have to react very, very quickly, you need to be able to have a motor that allows you to set the operating speed.

"The ICV lets you set the speed at which it opens or closes. Because you have a digital stepper motor, you can actually program it to move at the appropriate times at the appropriate speed, so it can address the specific application.

"We can cover the size range of valves we are offering - which is up to 2-1/2 inches - with only two motors. So there are a minimal number of parts. One of the first things you have to do when commissioning the valve is to tell the valve motor what size valve it is sitting on. You do this with the keypad on the valve motor. This way, the customer can keep a minimal stock if he is going to have an extra motor on hand.

"So, once again, just as with the mechanical valve, we have a three-part system. And the beauty of this design is realized, for example, when a tech is called into a job where a mechanical pressure regulating valve, let's say on the suction side, is not able to hold evaporator pressure where it needs to be because of wide variation in the load profile, variation in the refrigerated space temperature, or swings in head pressure.

"So, the customer wants to upgrade to a motorized valve which is going to be more intelligent. Traditionally that involved cutting out the mechanical valve, rewelding and doing some serious work to upgrade to a motorized valve. But because this new valve is designed for the same body whether mechanical or motorized, if you want to upgrade a mechanical servo valve to a motorized valve, the work is very easy. All you do is remove the four bolts, pull off the top cover, and take out the function module.

"From a parts perspective, other, more traditional valves can have up to 20 different kits to support valve repair. But with the ICV program, you have just three kits: a small, a medium, and a large function module, based on the valve port size. That's a minimal investment in spare parts.

"The technician doesn't have to remove up to 16 bolts. He has to remove only four, and he can get in there, swap modules, and be off the jobsite."

Davis summarized by saying that the Danfoss ICV platform offers a flexible solution, which combines a high degree of reliability and fewer installation and service costs, compared with a standard valve.

Publication date: 11/01/2004

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