Vacuum pump

Describes a technical device, which produces a vacuum or a high under-pressure.

CNC-machining centres in wood processing usually require vacuum pumps to tightly clamp the workpieces on the machine table using under-pressure. There are various designs, but in wood processing almost only 2 systems are used.

Rotary vane pumps

The most commonly used type of vacuum pumps in wood processing are rotary vane pumps. Here, a vane with variable wing length rotates eccentrically in a tube. The wings create separate chambers within the tube. Due to the eccentric shape and the variable wing length the chambers permanently change their volume. In this way, the rotary vane pump can also be used as a pressure generator, depending on the configuration of inlet and outlet.

  • Advantages: inexpensive, technically simple solution
  • Disadvantages: high wear of the impellers, relatively high noise level, maximum vacuum limited

Water ring pumps

Rarely used are water ring pumps for vacuum generation. Here an impeller with steady wing lengths is eccentrically rotating in a chamber. Instead of variable valve, liquid is located in the chamber. When rotating the impeller, the liquid is pressed to the walls of the chamber by the centrifugal force and thus forms a uniform ring. Because of the eccentric configuration, chambers between the liquid ring and the impeller are created, which constantly change their volume. By the appropriate arrangement of suction and pressure openings under- or over-pressure can now be generated.

This system works isothermal, so the air is not heated. Since the process heat must be dissipated to the liquid, a cooling is necessary.

  • Advantages: no wear on the impeller, no heating of the air, lower noise level, insensitive to small solids such as wood dust, therefore, very reliable working principle, liquid cooling can be simultaneously used as spindle cooling for the machine.
  • Disadvantages: more costly construction, fluid necessary, cooling circuit necessary, when leaks in the cooling system occur, the pump may fail and if a spindle is connected it might also fail; maximum under-pressure is limited, risk of corrosion, risk of deposits, air can saturate with liquid.

Centrifugal pump

Centrifugal pumps work with two identical spindles that rotate in up-cut direction like cog wheels. Simple centrifugal pumps create a wave shape that is similar to the shape of an eight, but there are pumps with more than two wings. Due to the non-contact running of the pistons they are working with dry running. The sucked in air thus is conveyed to the outlet via the outer sides of the chamber.

  • Advantages: insensitive to impurities in the sucked air

Vacuum pumps

In the woodworking industry these vacuum pumps have a minor role. In this category of pumps two spindles with pawls work in counter rotation synchronously in one housing. In- and outlet are arranged at the front face and are controlled by the corresponding osmission in the pawl spindle. To conduct a whole working cycle both spindles has to run a full rotation. During the first rotation the air is sucked in. During the secons the air is compressed and emitted at the end. This pump type is available in one-level or multi-level design.

  • Advantages: Dry runners that work without touching and thus has almost no wear, no need for additional media like liquid ring pumps, low noise
  • Disadvantages: no very high flow rates achievable

Screw pump

In screw pumps, two screw-shaped spindles move laterally into one another. To achieve a conveying feed effect the spindle has the coiling direction right and the other spindle left. Because of the geometric shape multiple chambers are created that continously convey the air at the housing wall from inlet to the outlet side.

  • Advantages: low noise level, continous conveying action (low pulsation)
  • Disadvantages: more expensive in the construction and the acquisition due to complicated design of the screw

Images

Vakuumpumpe, Kapazität 120 m³/h
Wasserringpumpe
Funktionsprinzip Wasserringpumpe
Funktionsprinzip Drehkolben
Klauenpumpe (Rovak)
Schraubenpumpe (Rovak)