Oerlikon Leybold Vacuum bucked the dry pump trend by designing an entirely new lineup of rotary vane pumps for the general R&D market.
Developed from the TRIVAC A and B series, the new TRIVAC NT dual-stage rotary vane vacuum pumps are optimized to offer an improved thermal profile, a lower noise level, and fewer compoments. The NT5, shown at left, provides a pumping speed in excess of 5 m3/hr. The NT10 and NT16 provide higher speed options. Image: Oerlikon Leybold Vacuum
The rotary vane pump is an elegant, classic design. Incoming gas enters the compression section of the pump, where there is a rotor mounted eccentrically inside a cylinder. The rotor includes slots that contain the vanes. As the rotor rotates these vanes compress the gas into a very small volume. The gas pressure increases from vacuum to atmospheric pressure.
The pumping action is highly efficient because it doesn't depend on fancy gearing or any other complicated mechanical structures. However, this method generates an appreciable amount of heat from the compression of air. Dissipation of this heat is a critical requirement of a pump system, and requires a sophisticated combination of air and oil circulation—often working in tandem—to bring operating temperatures down to reasonable levels. The higher the gas temperature, the less efficient the pump will be. If a pump gets too hot, it can degrade the oil more rapidly, and possibly lead to vapor backstreaming
The rotary vane pump's inherent simplicity could have stifled development, but Oerlikon Leybold Vacuum has made a concerted effort in recent years to put a new pump line on the market that benefits from advances in design and materials.
"We are one of the leaders in the market for mechanical pumps and we wanted to make sure we were still out there in front," says Brett Rock, market support manager for Oerlikon Leybold Vacuum USA, Export, Pa. "It was time to bring something new to the market."
That something new is the TRIVAC NT line, which was ushered in late last year.
Wholesale replacement of the TRIVAC B line
Oerlikon Leybold Vacuum has been manufacturing rotary vane pumps for much of its 156-year history. Over the years, new applications have emerged and others have faded, but by and large, the scope of uses for rotary vane style pumps is extremely wide. The TRIVAC NT line is intended for analytical engineering, automotive production, bulb and lamp manufacturing, freeze drying, industrial coating, and medical and process instrumentation, but is equally suitable for any general laboratory R&D purpose.
The dual-stage rotary vane design itself, however, has been overshadowed a bit in recent years by the bells and whistles of the newest high-vacuum pumps, many of which feature sophisticated electronic controls. The move away from traditional oils has resulted in efforts to displace wet pumps, such as the TRIVAC, with dry pump.
Some of these attempts have been successful, but many of the design changes that benefit other pumps have translated into improvements to the rotary vane lineup as well. New thoughts on pump cooling and overall efficiency led Oerlikon Leybold to make the bold—and in the industry, unusual—decision to revamp its entire rotary vane pump lineup.
"If you are going to do the design from scratch, you already know that size is an issue, cost is an issue, oil is an issue. You try to go across the board and try to make everything a little bit better for the end user," says Rock.
As a result, the company cites numerous improvements of the previous TRIVAC A and B series designs.
"(The TRIVAC NT) is quieter, about 3 dba or less. It runs cooler. There's less oil vapor backstreaming. There's less oil mist coming out of the exhaust. We've offered more precise control of the gas ballast flow and it's easier to maintain," says Rock.
These are a few of the improvements, but the most noticeable difference is in size. By reducing the parts count by 15%, Oerlikon's engineers were able to achieve several aims, including a reduction of the footprint by about 20%. Fewer parts also simplified maintenance—the entire inner section of the pump can be swapped out in minutes without special tools. The o-rings are also reusable, and the oil drain is sediment-free.
Despite the size difference, the vane pump itself is almost the same size as its predecessors, which allows easy replacement for users who upgrade their equipment. The other major difference—cooling—will become apparent to users over time.
"In order to make it cooler we've directed a lot of cooling air onto the inlet area to bring down the oil temperature and to cut down on things like oil backstreaming. Also, we've paid a lot of attention to the overall oil bath temperatures so that we have a longer oil life. Basically, it's about controlling the cooling airflow around the pump body," says Rich Tremblay, technical support specialist at Oerlikon Leybold Vacuum.
Effective cooling has helped reduce a major cause for shorter oil lifetime in the pump. The former design showed a backstream rate of 0.360 mg/h over the course of 65 hours of operation at an end pressure of 60 Hz. The improved design dropped the backstream rate to 0.044 mg/h, effectively elevating maintenance intervals. Over time, this will result in less oil use as well.
The TRIVAC NT, available in three flow rates: five, 10, or 16 m3/hr, runs at a sustained 1,000 mbar, and has a high water vapor tolerance.
Wet vs dry: a battle of dollars
A clean-sheet rotary-vane pump design to meet the changing needs of its customers, the TRIVAC NT has a smaller footprint, uses fewer parts, and handles heat dissipation more effectively. Despite the changes, the pump remains compatible with installations that depended on Oerlikon Leybold Vacuum's predecessors. Image: Oerlikon Leybold Vacuum
The development of wet pump technology has, in general, stagnated in recent years. Despite the breadth and scale of the market, competing low-vacuum pump designs have emerged that some believe have potential to displace pumps that depend on oil.
Dry pumps, in particular, have been hailed as a forward-thinking, environmentally-friendly solution.
The growth of dry pumps has been driven in part by new manufacturing sectors. The semiconductor industry, which is heavily dependent on toxic gases that could quickly break wet pump seals during lithographic processes, is basically forced to use dry pumps. The same is true for the burgeoning solar cell industry, which tends to use similar processes with silicon.
"In semiconductor applications, they are dealing with a lot of very nasty gases and they tended to rip these (rotary vane) pumps to shreds from the inside out. They go through oil like there's no tomorrow," says Rock. Also, the oil grades are very expensive.
The commercial success of dry pumps have prompted pump manufacturers in recent years to attempt to go in reverse, bringing the dry pump technology to other sectors.
Unfortunately, dry pumps remain expensive when compared to the old dependable wet pumps. They also tend to be more difficult and expensive to repair.
"It's not clear whether there's a real cost advantage over time" for switching to dry pumps. Which is why, Rock says, wet pumps will remain a popular choice for years to come.
"Wet pump technology will always have a future. People are always going to want to have an inexpensive, reliable way to get a vacuum or pump a gas. Dry pump technology is out there, of course, but it's much more expensive, especially when it comes to servicing it," says Rock.
The TRIVAC NT is about as all-purpose as pumps get. Certain gases are to be avoided—ammonia is highly destructive to the seals of any similar pump—but pretty much it's a general, all-purpose pump. Very few applications require the gas to be fulminized.
"Also, we have developed versions with brake fluid for those markets, and some with POE-type oils for the refrigeration-type market," says Tremblay.
Competing in a fickle, green marketplace
Even in the pump world, where pumping speed and ultimate performance are the primary goals, environmental and energy-conservation factors come into play.
"There's a push, especially from the OEMs, to try and get you to be more green," say Rock. These companies prefer to source parts from low-cost zones in the world. Lower power usage also equals less operation cost.
There's also the question of diversification. The wide range of pumping means that Oerlikon is forced to supply many types of pumps.
"You still want as much pumping speed as you can and as small a size as you can, but there's physical limitations of what you can do with the size of the pump," says Rock. "You still have to have a range; you are not going to find one pump, one solution everywhere."
Rock says as long there's oil in the ground, the wet pump will remain an economical and viable choice. There are still ways to improve it.
"For us, coming out with this TRIVAC NT pump is way to tell everybody ‘Look, we're not abandoning you, we're not going to force you to go dry. If you want a wet pump, we've got a wet pump,'" Rock concludes.
—Paul Livingstone
Resources:
Oerlikon Leybold Vacuum USA, Export, PA., http://www.oerlikon.com
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