In biological research laboratories, filtration techniques are performed to sterilize and clarify culture media, fine particles in solvents and buffers, and separate and purify samples for processing. In most cases, filtration can be performed faster when a vacuum is applied.
The majority of filtration tasks require low to medium vacuum, often not more than 120 to 50 Torr (25 28Hg). A number of plastic labware and filter device manufacturers recommend a maximum vacuum of 50 Torr (28Hg). However, glass labware makers have recommended no higher than 120 Torr (25Hg). In these applications, vacuum is commonly supplied by a house vacuum system, water aspirator or different types of vacuum pumps.
House vacuum systems are unreliable in providing a consistent, repeatable vacuum. Their vacuum performance is often tied into the number of users on the system at any given time and the types of solvent vapors being handled. Mistakes or misuse by one user can lead to unexpected down time for everyone relying on the system.
While water aspirators appear inexpensive initially, they continuously consume drinking water and create contaminated waste. Their vacuum performance is tied to the water pressure and/or temperature at any given time. If a volatile solvent is present, condensing vapors will contaminate the water, which is either flushed down the drain or collected and disposed of as hazardous waste.
Dedicated vacuum pumps offer an advantage over house vacuums and water aspirators in that they do not require water utilities or drains and are unaffected by the actions of others. Rotary vane pumps require the use of lubricating oils for normal operation. These pumps require regular changes and disposal of contaminated pump oil to prevent downtime and expensive repairs. For most common applications in biological research, the rotary vane pumps provide significantly more vacuum than is required.
Low and medium vacuum is suitably provided with an oil-free, dry diaphragm pump. These pumps employ a simple operating principle: An elastomeric diaphragm is moved up and down by a rotating eccentric. During the descending stroke of the pump, it draws in the gas through the intake valve. In the ascending stroke, the diaphragm forces the gas through a discharge valve and out of the head. The diaphragm mechanism enables quiet, reliable oil-free performance with little or no maintenance required.
A brand of diaphragm pumps is the KNF LABOPORT filtration line. These pumps have been engineered specifically for the most common applications in biological research labs. KNF combines their over 50 years of experience and over 300 patents in diaphragm pump technology to create this small, quiet, reliable line of vacuum pumps.
The KNF LABOPORT Filtration Series is designed for most common lab applications, including bottle top, single-use or vacuum manifold filtration applications. With flow capacities from 5.5 to 35 liters per minute (L/m), the pumps can be employed in numerous tasks including sterile filtrations in microbiological labs, solvent filtration in HPLC labs and sample preparation in bacteriological experiments. A multi-port valve system design enables these pumps to withstand exposure to liquid condensate; in fact, vacuum performance is reliable even with the occasional intake of liquid. Corrosion-resistant parts are used within the pump head. KNF Filtration pumps may be equipped with vacuum gauges and bleeder valves to improve pressure control for sensitive vacuum adjustment.
KNF Neuberger offers a comprehensive line of diaphragm pumps for laboratories, complete with accessories and technical assistance for pump selection. The KNF web site includes actual testimonials from working chemists and scientists. Visit www.knf.com/labselection.htm for more information.