Physical Basics: Pumps

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Active Priming

In some applications, the hydraulic setup doesn’t allow for customization, which can hamper passive priming. In these cases, priming needs to be obtained actively with a third-party suction device.

The suction device can be for example:

  • A syringe (common practice in small scale bio-processes)
  • A positive displacement pump, such as
    • peristaltic pump, common in bio-processing
    • air operated diaphragm pump, in semiconductor industry
  • An Venturi nozzle aspirator, commonly used in Semi industry.

Other than using a suction device, in certain cases it is also possible to obtain priming by directly filling the pump head with fluid, or by pressurizing the upstream tank.

Active Priming by Suction Device in Bio-Processing

In lab-scale bio-processes, it is common practice to use small bio-reactors with ports on the head plate only and no bottom outlet (in Figure 1 an example of such reactor).

With this kind of bio-reactor, the fluid will not passively flow into the pump.

Figure 1: example of bio-reactor for laboratory scale cell culture (source: Thermo Fischer Scientific)

When this problem occurs, priming can be addressed by installing a suction device in series with the pump, to evacuate the air from the suction line (see schematic in Figure 2).

Figure 2: Schematic of the installation of a suction device to remove the air from the suction line and prime the pump

Such suction device can be either a positive displacement pump (e.g. a peristaltic pump), a syringe, or an aspirator. After priming is completed, the suction device can simply be removed or bypassed. The video below shows how actively prime a Levitronix pump using a peristaltic pump.

Filling the Pump Head with Fluid

In the application cases where sterility or cleanliness are not a top priority (e.g. during the evaluation phase of a newly designed tool), it might possible to pour fluid into the suction line and pump head directly. As a result the pump will be primed and it can be started. Such procedure might require some adaptions in the hydraulic loop (i.e. using pinch valves) in such way that the pump doesn’t empty immediately after having it filled.

// FILLER WITH A PICTURE?

Tank Pressurization

In addition, the upstream tank can also be pressurized. As a result some fluid will be pushed into the pump, and the existing bubbles will be compressed to a smaller volume. Once the bubbles are small enough, they can be easily flushed away by the flow rate.

Figure 3: pressurizing the tank will push fluid into the pump and compress the air bubbles. When the bubbles are small enough, they are easy to flush away.
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