Syringe Pump Operating Modes Explained: Infuse, Withdraw & More

When a syringe pump doesn't behave the way you expect, remember to check the operating mode. Different operating modes are designed for specific types of protocols. Choosing the wrong one doesn't always trigger an error; but, it might produce wrong results.

We will provide some scenarios to help you match the modes to your experiment.

Scenario 1: You need continuous flow for hours, but your syringe runs out mid-experiment

Mode: Infuse

Standard infuse mode pushes fluid at a constant rate until the syringe is empty. For short runs, this is straightforward. For long-duration experiments, a single syringe creates an unavoidable interruption when it empties.

If your application requires continuous flow with minimal interruption, a dual-channel continuous pump is the right choice. One channel infuses while the other channel reloads, allowing the pump to switch between channels. Compared with a single-channel pump, which requires a refill pause during continuous operation, a dual-channel design significantly reduces flow interruption and provides smoother delivery.

Scenario 2: You need to withdraw liquid from a vessel at a controlled rate

Mode: Withdraw

Withdraw mode retracts the plunger to aspirate fluid from a connected source. It's the correct choice for any cases where you're pulling fluid in rather than pushing it out.

Watch for: loose tubing connections. Withdraw mode creates negative pressure at the inlet. Any leak will draw air into the syringe instead of sample. Before starting, verify every connection is airtight and check for bubbles during the first few seconds of operation.

Scenario 3: You need to deliver fluid and then withdraw it

Mode: Infuse-then-Withdraw

This mode completes a full infusion cycle and then automatically reverses to withdraw. It is designed for laboratory protocols that require sequential fluid delivery and retrieval, such as reagent transfer and recovery, flushing and rinsing cycles, or fluid transport experiments where liquid is first delivered and then withdrawn.

Watch for: If your experiment requires a waiting period between the infusion and withdrawal phases—for example, to allow sufficient reaction, mixing, or contact time—set the puase time at the transition point. The pump supports a programmable pause between the infuse and withdraw phases.

Scenario 4: You need to draw in fluid before dispensing it

Mode: Withdraw-then-Infuse

When the syringe is not pre-filled, Withdraw-then-Infuse allows the pump to first draw liquid from a source into the syringe and then automatically switch to infusion. This is useful for laboratory workflows that require controlled fluid loading followed by precise delivery, such as reagent handling, sample transfer, or automated liquid-handling experiments.

Watch for: air bubbles entering the syringe during the withdrawal phase. If the inlet tubing is not fully primed before the run starts, air may be drawn into the fluid path. Prime the tubing before the first cycle, or use a slow initial withdrawal to help remove trapped air before beginning the experiment.

Scenario 5: Your protocol requires rhythmic, back-and-forth flow

Mode: Cyclic

Cyclic mode alternates between infuse and withdraw repeatedly — either for a set number of cycles or indefinitely. 

Watch for: Each change in direction creates a brief transition as the pump switches between infusion and withdrawal. For applications that require highly stable or continuous flow, consider whether these flow transitions may affect your experimental conditions before using this mode for extended runs.

Scenario 6: You need to deliver the same volume repeatedly, with a rest period between each injection

Mode: Multiple Infusion (available on USS-SP00013 and USS-SP00018)

Multiple Infusion mode divides the total syringe volume into a series of equal injections, with a defined rest interval between each one. For example: a 10 mL syringe, 2 mL per injection, 5 injections total, with a 10-minute rest between each — the pump handles the entire sequence automatically.

Two details that matter:

• Interval Time is measured from the end of one injection to the start of the next — not from start to start. If you need a 10-minute gap between doses, set 10 minutes. Don't subtract the injection duration yourself; the pump does not do that automatically.
• Single injection volume × number of injections must not exceed the syringe capacity. If it does, the pump will display an error before starting. Size your protocol to fit within the loaded syringe volume.

This mode is available on the USS-SP00013 and USS-SP00018 models. If timed, repeated dosing is central to your protocol, these are the models to consider.

Finding the Right Model

Different protocols call for different mode availability, channel count, and accuracy. U.S. Solid's syringe pump lineup covers single-channel and multi-channel configurations, standard (≤±0.5%) and high-precision (≤±0.1%) accuracy, and models with Multiple Infusion mode for timed dosing protocols.

Browse the U.S. Solid syringe pump lineup to find the model matched to your application.