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Self-Drying Vacuum Pumps... the solution for applications producing condensation

by Erwin Hauser, Chief Engineer, KNF Neuberger, GmbH.

Where gases with high moisture content must be evacuated during vacuum drying operations, condensate may collect in the vacuum pump head. Consequently, the pump may not perform properly and may take more time to evacuate the designated volume. New, self-drying pumps clear moisture from the pump head during the evacuation process and thus dramatically increase pump efficiency.

Vacuum is an integral part of the laboratory. While vacuum in the past was produced using central house systems, rotary vane or by water jet pumps, diaphragm pumps have recently become the standard. Diaphragm pumps use no oil and do not contaminate media. They are universally resistant to chemicals, require little maintenance, are gas tight and versatile. They also provide the optimum condition from an economic and environmental standpoint.

It is only in applications where larger amounts of condensate are produced that conventional diaphragm pumps run into difficulty when some condensate collects in the pump head. The results are a poorer vacuum and much longer evacuation times.

Automatic Drying
To solve this problem, KNF Neuberger has developed a series of PowerDry vacuum pumps based on a diaphragm principle that include a sophisticated self-drying system (patent pending). These new pumps blow the fluid out of the pump heads at high speed during the evacuation process. As part of the process, the pump heads are ventilated using a solenoid valve while the vacuum remains constant in the process. After the pump heads are dried, the pumps produce a much better vacuum and evacuates faster. Practical experiments using a vacuum drying oven revealed a measurable efficiency increase thanks to the PowerDry system.

The self-drying vacuum pump makes the system mo re flexible. It runs independent of the pump and can be switched on as needed. If the system is turned off, the pump operates in the usual way. The versatility of the system is demonstrated further by the ability to adjust PowerDry to specific process requirements.

The control system differentiates between three variables:

t1: the amount of time between switching on the drying system and the first ventilation cycle of the pump head,

t2: the amount of time for ventilating,

t3: the amount of time between the ventilation cycles.

Although the values for t1, t2 and t3 are set at the factory, they can be modified at any time when the drying system is powered down. Operators have a choice of 10 values for each setting.

Self-Drying Pumps Powerful and Reliable
KNF vacuum pumps equipped with the PowerDry system are based on both simple and strong technologies. Diaphragm pumps are sturdy and reliable, in part because of 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 to be delivered through the intake valve. In the ascending stroke, the diaphragm compresses the gas through a discharge valve and out of the head. Several stages may be utilized.

The valves of the diaphragm pump are automatically controlled and utilized for the drying system. During the intake process, the discharge valve (elastomer disk) is sealed closed and compressed by the pressure ratio while the intake valve opens. During discharge, the process is reversed.

As one of the worlds leading pump manufacturers, KNF Neuberger has applied the principle of diaphragm pumps successfully to application-oriented and high-performance products for over 50 years. On e example of the companys innovative developments is the structured diaphragm used in self-drying pumps. This patented diaphragm increases pneumatic performance and results in longer service life than that provided by conventional flat diaphragms. The structured diaphragm also allows for the manufacture of smaller sized pumps. And, thanks to the smooth diaphragm surface, it has good chemical stability and gastightness compared to flat membranes still in wide use today that employ clamping disks.

Sophisticated System
Uncomplicated and yet ingenious, sturdy and reliable all words appropriate to describe the new PowerDry system. It is based on the pressure differential between pumping chamber and the atmosphere: when the solenoid valve in the drying system opens, air at atmospheric pressure and at a high flow rate streams into the pump head while under vacuum. Due to the pressure ratios, the intake valve on the suction side of the pump automatically seals off the suction port so that the vessel vacuum is maintained. The intake valve functions as a kind of automatic non-return valve. In contrast, the discharge valve of the pump opens because of a sudden increase in pressure. It produces a continuous, directed flow of air that forces the condensate through the second head and out the pump.

Once the solenoid valve of the drying system closes again, the pumps intake valve opens automatically and evacuation of the vessel resumes. Evacuation continues until time for a new drying cycle. Electronically controlled, the entire drying cycle lasts only two seconds.

By introducing PowerDry vacuum pumps, KNF Neuberger opens the door to new opportunities for laboratory users. Evaporative processes which develop large amounts of condensate finish faster and more effective with the PowerDry system. A welcome result is a reduction in noise, since pumps burdened with unwanted fluids exhibit increased diaphragm and valve noises.

Self-drying pumps are ideal for all processes that deliver gases with a very high percentage of moisture. For that reason, the vacuum drying oven application is a typical example.

Model N842.3FT.40P (left) & N860.3FT.40P shown.

The new product line consists of four products with the following performance range:

delivery rate: between 20 and 60 L/min (air at 20C under atmospheric conditions),

ultimate vacuum: between 3 and 7 Torr.

A Summary of Facts & Features

Diaphragm vacuum pumps with on/off control of the PowerDry system,

The PowerDry system is deployed whenever gases with a very high percentage of moisture are delivered (e.g., drying ovens),

The PowerDry system ventilates the pumps heads so that the condensate is blown out of the pump during the evacuation process; the pump thus evacuates faster and more efficiently,

While the pump heads are ventilated, the vacuum in the evacuated chamber is maintained.

The ventilation process can be adapted to individual requirements by setting time and duration of ventilation on the controls.

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