Water aspirators, once a staple in many biology and chemistry labs, are becoming an increasingly uncommon sight. These devices connect to a lab faucet, and as water flows through a narrowing tube inside the aspirator, its velocity increases, creating a vacuum in the connected sidearm. Their historic popularity stemmed mainly from their low purchase price. But a closer look at the performance, environmental impact, and lifetime cost of a water aspirator may help convince lingering aspirator enthusiasts that it’s time to switch to a vacuum pump.
Water aspirators are capable of producing a moderate vacuum, in some cases reaching as low as 10 torr. While suitable for use in rotary evaporation or filtration systems using funnels or solid-phase extraction cartridges, water aspirators do not reach the deeplevel vacuum required for certain applications, such as evaporating high-boiling-point solvents, according to Jason Wagner, vice president of marketing in North America at BÜCHI Corporation (New Castle, DE). As Peter Coffey, vice president of marketing at VACUUBRAND (Essex, CT), explains, another drawback of water aspiration is that the end vacuum depends on the water pressure of the faucet and the water temperature. “A water aspirator that produces good vacuum when used alone may not produce adequate vacuum when used in a lab with other simultaneous users, as the water pressure may be sufficiently reduced to compromise vacuum generation,” says Coffey. “Also, water temperatures vary seasonally, so water that is naturally warmer in the summer than in the winter will produce less vacuum.” With an inconsistent vacuum, experiment replication becomes a challenge.
“Environmental impact is really where water aspirators fall short,” according to Roland Anderson, laboratory products manager at KNF Neuberger (Trenton, NJ). Intensive water use is a major concern with water aspiration, which requires a continuous flow of water from the tap. With moderate daily use of the device wasting an estimated 50,000 gallons of water per year, water aspiration is subject to increasing regulation. Anderson adds that water aspiration often leads to water contamination, as these devices can draw up volatile solvents, which then get carried through the device and down the drain. “So there’s a pretty significant environmental impact, both in terms of wasted drinking water and pollution,” he concludes. A recirculating water aspirator can help mitigate wastage. However, both Coffey and Anderson note that these devices still pose a contamination risk and require that the resulting water be treated as hazardous waste.
A simple aspirator can be purchased for as little as $50. But Anderson argues that the real cost lies in the cost of ownership—the copious use of running water and having to dispose of hazardous waste. Additionally, water aspirators run the risk of causing lab flooding if a sink drain gets blocked during use, which could result in an enormous cost.
Vacuum pumps solve many of the problems associated with water aspirators. An environmentally friendly alternative, vacuum pumps completely avoid the issues of water waste and contamination. And by eliminating the water use and treatment costs associated with an aspirator, the initial cost of a vacuum pump potentially can be recovered in a few years.
Where water aspirators fail to provide a deep enough vacuum for certain uses, vacuum pumps deliver. A simple dry lab pump can reach about 1 torr, which Coffey notes is deep enough to handle most lab applications. And an oil pump can achieve a substantially deeper vacuum; however, Wagner points out that oil pumps also require more maintenance and can become contaminated. Use of a vacuum pump provides the user with greater control over the vacuum, which leads to improvements in key lab applications; for example, a vacuum pump reduces bumping during evaporation.
“While the initial cost of a vacuum pump is greater than [that of] a water aspirator, the flexibility, performance, reliability, and environmental impact are strong arguments for adopting a well-established solution in the industry,” says Wagner.
For additional resources on vacuum pumps, invluding useful articles and a list of manufacturers, visit www.labmanager.com/vacuum-pumps