Proper Micropump Priming with The Bartels Pump | BP7

While the BP7 micropump is capable of self-priming in many situations, proper initial micropump priming, ensuring the pump and fluidic path are free of trapped air, is essential for achieving stable and efficient performance. Microfluidic systems are especially sensitive to the presence of air, and incomplete filling of the pump can severely limit functionality.

Why Proper Micropump Priming Matters

As discussed in the article The BP7 Micropump: A Practical Microfluidic Workhorse, residual air inside the pump can lead to:

• Disrupted flow or inconsistent output
• Poor sealing behavior of the internal flap valves
• Reduced stroke efficiency due to compressibility
• Unreliable dosing or delayed response times
• Potential long-term wear from cavitation or vibration stress

These issues are particularly noticeable at low flow rates or when working with viscous fluids, where micropump priming becomes even more challenging.

Is the BP7 Self-Priming?

Yes, but with limitations.

The BP7 can self-prime, meaning it is capable of drawing in fluid from a reservoir even when initially dry, provided:

• The inlet is not too far from the fluid source (i.e., minimal suction height)
• No major air blockages or bubbles are present in the tubing
• The system is properly sealed and leak-free

However, for optimal startup performance, especially in critical applications or sensitive systems, we strongly recommend actively priming the pump before operation.

Practical Micropump Priming Methods

1. Syringe Priming (Recommended Manual Method)

The syringe pull-through method is the preferred and recommended priming technique for first-time setup, laboratory use, and system integration.
It is fast, reliable, and requires no additional equipment beyond standard lab tools.

Required Initial Setup

Before priming, ensure that the pump is installed in a basic operating setup:

• The pump must be electrically connected and controllable
  (e.g. via the mp-Multiboard2 that is connected to a PC or tablet with Bartels FluidicStudio installed and opened, an appropriate pump driver, and the pump cable)
• A liquid source must be available and connected to the inlet side of the pump
• The outlet must be accessible and connected to tubing

The pump does not need to be actively driven during this priming step.

Step-by-Step Priming Procedure

1. Connect a liquid reservoir to the pump inlet
   Use a needle attched to the tubing and connect it to the inlet side of the micropump.
2. Connect a syringe to the pump outlet
   Attach the syringe to the tubing connected to the pump outlet using a suitable tubing connector to ensure an airtight seal.
3. Pull liquid through the pump
   Slowly draw the syringe plunger to pull liquid from the reservoir through:
   • the inlet tubing
   • the internal pump chamber
   • the outlet tubing
   This process removes trapped air from the pump and all connected fluidic paths.
4. Observe the flow
   Continue pulling until a steady, continuous, and bubble-free liquid stream is visible in the tubing and syringe.
5. Disconnect the syringe and finalize the setup
   Carefully remove the syringe while keeping the tubing filled with liquid.
   Attach the downstream components required for your specific application.

Advantages of This Micropump Priming Method

• Highly effective at removing air bubbles
• No pump actuation required
• Minimal equipment and setup time
• Ideal for initial priming and troubleshooting

For most use cases, this method provides the most consistent and predictable results and should always be attempted before alternative priming techniques.

Watch video instructions here:

2. Vacuum Priming (Production-Grade Method)

In our in-house production process, we fill the BP7 micropump with water by applying an external underpressure using a vacuum pump. This method:

• Evacuates all internal air
• Forces liquid into the pump chamber and through the internal channels
• Guarantees a bubble-free start for performance testing

This approach is highly reliable and can be easily replicated with lab vacuum setups.

3. Priming by Frequency Sweep (Active Method)

If manual priming isn’t an option, you can sometimes dislodge trapped air bubbles using the pump itself:

• Run the pump with a frequency sweep: vary the actuation frequency from low (~50 Hz) to high (~300 Hz)
• This alters the diaphragm dynamics and can help move or release stubborn air pockets
• Use this method when small bubbles remain even after pre-filling

Note: This technique may take longer and is less predictable than vacuum or syringe micropump priming.

General Recommendations for Priming Success

• Always check tubing and connectors for bubble traps or leaks before priming.
• If you’re switching media (e.g. water to alcohol), flush thoroughly to avoid degassing effects that can cause bubbles to form post-priming.
• For permanent setups, consider adding a priming port or bypass to simplify startup routines.

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Important note:

Even after successful micropump priming, it’s good practice to stay mindful of how the system evolves during operation.

• In rare cases, dissolved gases in the liquid may slowly come out of solution and form small air pockets, especially in low-pressure areas. If they accumulate, this can slightly affect flow stability over time.
• Similarly, if a small air bubble remains after an imperfect priming, it might shift or dissolve during operation, potentially leading to small changes in flowrate, either increases or decreases.

That said, in a properly degassed liquid system with good sealing, the BP7 typically delivers very stable flow over extended periods. A flow sensor can be a helpful addition to monitor and detect such variations if high precision is required, allowing early detection and correction without disrupting the process.

Proper micropump priming isn’t just a preparation step, it’s a vital part of ensuring that the BP7 performs as designed. With just a little attention at the start, users can avoid many of the pitfalls commonly encountered in microfluidic systems and get the most out of their pump from the very first cycle.