A new breed of vacuum pump claims to improve significantly on traditional diaphragm designs, offering benefits in performance, reliability and longevity of operation
The developments are a derivative of the Wob-L piston pump invented and patented by Arthur Droege and Richard Bell of Welch's parent company Thomas.
The Wob-L principle is based around a small, high speed, direct connected motor compressor which has a unitary piston and piston rod whereby the piston wobbles in the cylinder as the crankshaft rotates.
The wobbling piston is sealed to the cylinder by a flanged disk cup, which forms both a seal and mechanical guide for the piston and which runs without lubrication in contact with a low friction, surface coated cylinder of high heat conductivity.
Simplicity is the key to the economical design.
As the piston wobbles, air resistance on the upward stroke expands the disk's seal on the piston to increase its efficiency, while compensating for the wobble action.
And as a piston pump, an inherent characteristic of the design is that the failure mode is a gradual wear-out, rather than the catastrophic failure mode that is a characteristic of many other designs.
Taking its name from its principle of operation, the Wob-L piston compressor was radically different from any other design on the market at that time, and was a signification innovation for Thomas.
It provided a design that would meet the demands of the most challenging of environments. In particular, its oil-free operation also made it extremely popular in the medical, automotive and beverage industries. Ongoing development of the product saw the introduction of new materials for key components.
For example, a PTFE sintered cup was introduced, extending lifespan to some 25,000 hours in some environments.
Now Welch has pushed development forward again, with a range of Wob-L pumps designed specifically to address the requirements of the laboratory market.
Designed and built to operate at the pressures and vacuum levels required in laboratory applications, the pumps eliminate the problems of unreliability and frequent breakdowns that beset oil-sealed rotary pumps.
At the same time, the pressure against flow rate and vacuum against flow rate curves for Wob-L pump designs are superior to those of membrane pumps, giving far higher flows at any given pressure or vacuum to ensure a more consistent operation and giving longer life operation, or allowing a physically smaller pump to be used to perform any given task.
Oil free, the pumps run without the possibility of contaminating the process with oil mist.
The design is also extremely reliable compared to membrane pumps, as demonstrated by the documented examples of Wob-L pumps employed in applications in the medical sector giving lifespan in excess of 25,000 hours continuous running.
Laboratory-specific Wob-L pumps are being introduced to cover applications across the whole spread of laboratory applications.
A good example is the Model 2522, which has been developed to replace water aspirators, or for use in standard duty applications such as vacuum filtration. This dry vacuum pump combines performance with affordability and incorporates user features such as vacuum and pressure regulators, and catch pots to prevent accidental ingestion of liquids and to prevent damage to the pump in an accident.
The pump provides pressures to 100psi and vacuums to 78mbar, with free air flow rates of 45l/min.
Another example is the Model 2510 dry vacuum/pressure station - a model in which Welch has defined a new format of laboratory pumps.
Compact, light and highly portable, the economical station is designed general duty laboratory applications where only a rough vacuum or moderate pressure required.
While providing all the operating advantages of the Wob-L design principle and an ergonomically designed, aesthetically pleasing housing, the 2510 also breaks the important £200 price barrier to provide an extremely cost effective solution.
The station is used in applications such as filtering, drying, aerating and gas sampling, and is an ideal replacement for water recirculation pumps or water aspirators. The station is easy to connect to laboratory apparatus via the hose connection point on the face of the unit.
It provides free flow rates of 11l/min, vacuum to 292mbar and pressure to 2.3bar. Smart and attractive, the 2510 has been designed from the outset as a lightweight, compact portable unit, with the pump housed in a tough injection moulded housing with an integral carrying handle.
Volume manufacture has been the key to producing such a high performance, visually pleasing unit at such a cost-effective price.
For analytical instruments and techniques including mass spectrometers, electron microscopes, gas analysers and backing compound or hybrid turbomolecular pumps, Welch has also developed a very compact 100l/min Wob-L pump that has an ultimate pressure of 4mbar and with very high flow rates in the critical 10mbar to 30mbar region.
Such a pump again confirms the advantages of this Wob-L design.
