Vacuum Pump Technologies

   In this section, we list the typical vacuum technologies found on a medical vacuum system

Rotary Vane:

      There are (2) styles, or types, of rotary vane vacuum pumps. The 1st is a lubricated rotary vane pump and the 2nd is a dry rotary vane pump. The principles of operation of the two are very similar. The operating principle is this: a rotor, connected to the motor shaft, is turned inside of a housing. The rotor is not in the center of the housing but offset so that there is more space on one side of the housing than the other. Cut into the rotor are slots (the number of slots will vary with pump hp and manufacturer) that vanes "slide" into. As the rotor turns, the vanes are free to "slide" in and out of the rotor slots. As the rotor turns, the vanes get pushed out and up against the pump housing. There is a pocket of air that is trapped in the space between each of the pumps vanes. As the rotor spins, this space is first increased (the suction side of the pump) and then decreased (discharge side of the pump). As the air is compressed, it is then pushed out of the pumps discharge. 

• Lubricated rotary vane pumps use oil to "lubricate" or create the seal between the tip of the vanes and the pump housing. Typical maintenance of this type of pump is: oil changes, oil filter changes and exhaust filter changes.

• Dry rotary vane pumps do not have any oil in them. The tip of the vanes come in direct contact with the pump housing. The vanes are typically made out of a carbon based material. Typical maintenance of this type of pump is: vane changes.

Liquid Ring:

      As the name implies, liquid ring vacuum pumps require a liquid to create a seal inside the pump. For medical applications, liquid ring pumps are sealed with either water or oil. The operating principles of the two are the same: an impeller, which is offset so the impeller is not in the center of the pump housing, rotates and traps pockets of air in the space between the impeller fins. The impeller is typically made of brass and has fixed fins. As the impeller turns, there is a pocket of air that is trapped in the space between each of the fins. This space is first increased (the suction side of the pump) and then decreased (discharge side of the pump). As the air is compressed, it is then pushed out of the pumps discharge.

      A liquid is required to create a tight seal between the tip of the impeller blades and the pump housing. There are (3) different ways a liquid ring pump utilizes the sealing fluid.

          1.) a "once thru re-circulating" system (can only be operated using water as the sealing fluid - not oil): sealing water is introduced into the pump, discharged, and sent directly down the drain. This type of system is very simple in design but  does require copius amounts of water to operate.

           2.) a "partial re-circulating" system (can only be operated using water as the sealing fluid - not oil): sealing water is introduced into the pump and discharged. Some of the discharged water is re-circulated and used again to seal the pump. This type of system is relatively simple in design and, since some of the water is re-used, it does not require as much water as the "once thru" to operate.

           3.) a "total re-circulating" system (can be operated using water or oil as the sealing fluid): sealing fluid (water or oil) is introduced into the pump and discharged. The discharged fluid (water or oil) is cooled via an air to liquid or liquid to liquid heat exchanger. The cooled sealing fluid is then used again to seal the pump. This type of system requires some type of heat exchanger system to cool the discharged sealing liquid before it can be introduced into the pump again. If water is used as the sealing fluid, only a small amount of fresh water is needed... this is due to any water that may evaporate*. If oil is used as the sealing fluid, very little oil is "consumed"... the only oil that is lost is oil that does not get reclaimed via the discharge oil filters.

     * there is a unique liquid ring total re-circulating pump design (offered in the medical market) that may actually "make" water. Depending on the moisture level, temperature, and pressure, the water vapor in the incoming air stream may condense and actually add water to the system. Call or email us for more detailed information on this type of liquid ring pump.

Dry Non-Contacting Claw:

      This type of pump has a completely dry vacuum chamber (no water or oil in the vacuum chamber). Two "claws" rotate in opposite directions pulling in air, compressing the air, and finally pushing it out the pumps exhaust.  The tolerances are close, but the (2) claws do not come in contact with each other or the pump housing. A small amount of oil is needed to lubricate (2) synchronizing gears at the end of the claws shafts. This oil never enters the vacuum chamber.

Regenerative Blower:

      This type if pump uses an impeller fan with curved "blades" that rotate in a circle via the motor shaft. The impeller never touches the pump housing. In addition, it does not require any water or oil to operate - it's a completely dry type of vacuum pump. To get a deeper vacuum level more "stages" or impellers are installed by the manufacturer. A regenerative blower with (1) impeller may reach a vacuum level of approximately 7" Hg gauge while a pump with (3) impellers may achieve 25" Hg gauge.

Screw:

       A screw vacuum pump utilizes (2) shafts that are cut similar to a screw you'd use to hold a piece of wood down. The grooves of each shaft overlap and they get closer and closer to each other near the discharge end. Vacuum is created by pulling air into the spinning grooved sections. The air is squeezed into a smaller and smaller space until it is finally discharged to atmosphere.

© 2006, Medical Gas Info. All Rights Reserved