How can you keep a small flow steady for hours when one syringe runs out in minutes? Many labs face this problem.
A continuous flow syringe pump is a pump that uses two syringes and a valve. One syringe fills up while the other pushes liquid out. This way, the flow never stops.
A normal syringe pump stops when its syringe is empty. This guide uses real data from DK Infusetek's continuous flow syringe pump range. You will learn how it works, the two models, the specs, and the main uses.
What Makes Syringe Flow Truly Continuous?
When the syringes switch, the flow continues, making it really continuous. There is just one syringe in a normal pump. The length it can run depends on the syringe size. The flow stops when the syringe is empty.
We can remedy this with a continuous syringe pump. Just like a microliter syringe pump, it is very precise, yet it never stops. This pump is marked as Constinfuse® by DK Infusetek. At a steady rate, it moves very tiny amounts of liquid.
Continuous Flow at a Glance
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Feature
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Detail
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Main parts
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Two pump units and a switching valve
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How it refills
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One syringe fills while the other pushes
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Liquid amounts
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Microliter-scale transfer and dispensing
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Brand name
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Constinfuse® by DK Infusetek
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How a Continuous Flow Syringe Pump Works
A continuous flow syringe pump works by using two syringes that take turns. A valve links the two. Liquid only flows out from the syringe that is pushing.
Two Syringes Working as One Steady Stream
The two pump units work in turns. Syringe A pushes liquid out. At the same time, syringe B fills up. Then they switch. This gives one smooth, steady flow.
Why the Reversing Valve Matters So Much
The reversing valve links each syringe to the inlet or the outlet. On the CFSP-I/CU-I, it is a 3-port 120° valve. The valve body is PCTFE, and the core is PTFE. Closed-loop control and overload protection keep the syringe safe.
A 2024 study found that check valves can upset smooth flow below about 100 μL/min. So in any low flow syringe pump task, the valve matters as much as the motor.
Dual Syringe Pump vs Standard Syringe Pump
A dual syringe pump keeps the liquid moving, even while it refills. A standard syringe pump must stop to refill. When DK Infusetek launched Constinfuse®, it pointed out the problems with other pumps:
Piston pumps pulse each time the piston moves.
Peristaltic pumps slow down as their tubes wear.
Early push-pull syringe pumps kept going, but their flow did not stay steady for long.
Pump Types Side by Side
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Factor
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Standard syringe pump
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Push-pull syringe pump
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Constinfuse® design
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Flow during refill
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Stops
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Runs, less steady
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Runs steadily
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Long runs
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Limited by syringe size
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Hard to keep steady
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Made for long runs
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Syringe setup
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One syringe
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Two, push and pull
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Two, with a switching valve
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Best use
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Short doses
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Basic transfer
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Long, small-volume feeds
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Can your work stop for refills? Then one syringe may be enough. If it cannot stop, a continuous flow syringe pump is the better choice.
Two Continuous Syringe Pump Designs Compared
DK Infusetek makes two models. The CFSP-I/CU-I comes with a separate controller. The CFCU-I has everything in one box. Both take the same syringe sizes, and both are just as accurate.
CFSP-I/CU-I: Pump Unit Plus Controller
The CFSP-I/CU-I controller-based pump has four modes: continuous transferring, fixed volume measurement, dispensing, and timing start/stop. Its pump units can also work "offline." So one controller can set each unit in a different way. The outer case is 304 stainless steel with a spray finish.
CFCU-I: Integrated Dual-Actuator Design
The CFCU-I dual-actuator pump has two drives in one unit. Its own software checks and adjusts the flow. So it works as a constant flow syringe pump with very little pulse. The body is stainless steel with a powder coat. Custom stepper motors help it run quietly.
CFSP-I/CU-I vs CFCU-I at a Glance
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Spec
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CFSP-I/CU-I
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CFCU-I
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Flow range
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0.06 μL/min to 70 mL/min
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0.07 μL/min to 70 mL/min
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Working modes
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4
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3 (Continuous Transfer, Volumetric Metering, Timed Metering)
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Control
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4.3-inch LCD, touch screen and keypad
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PC through RS232/RS485, plus switch signals
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Valve options
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3-port 120° valve (PCTFE body, PTFE core)
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Ceramic, PTFE or PEEK (3-way)
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Power
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Controller ≤10W, pump unit ≤60W
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≤60W
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Key Specs Every Precision Syringe Pump Needs
A precision syringe pump is judged by four main specs: flow range, dispensing volume, accuracy, and pressure limit. Both continuous flow syringe pump models have the same numbers here:
Dispensing volume: 0.1 μL to 25 mL
Accuracy: error of ±0.1% or less, when the stroke is at least 30% of the full stroke
Highest liquid pressure: 0.68 MPa
Tube fitting: 1/4-28UNF
Connection to other devices: RS232 and RS485, Modbus RTU
Where it can work: 15°C to 40°C, with humidity below 80%
Flow Range Across Each Syringe Size
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Syringe size
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Minimum flow
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Maximum flow
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50 μL
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0.0625 μL/min
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608.37 μL/min
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100 μL
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0.125 μL/min
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1.21 mL/min
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250 μL
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0.3125 μL/min
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3.04 mL/min
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500 μL
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0.625 μL/min
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6.08 mL/min
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1.0 mL
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1.25 μL/min
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12.16 mL/min
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2.5 mL
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3.125 μL/min
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30.41 mL/min
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5.0 mL
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6.25 μL/min
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60.83 mL/min
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10 mL
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12.5 μL/min
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70.00 mL/min
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25 mL
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31.25 μL/min
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55.00 mL/min
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Check the last two rows. The 10 mL syringe goes up to 70 mL/min. But the 25 mL syringe only goes up to 55 mL/min. So a bigger syringe is not always faster. These rates were tested with pure water. The inlet tube was shorter than 1 m, with a 1.6 mm inner diameter.
Microliter Syringe Pump Accuracy Explained
The ±0.1% accuracy only applies when each stroke uses at least 30% of the full stroke. For a 1.0 mL syringe, each stroke must be 0.3 mL or more.
With a microliter syringe pump, the syringe you choose changes how much liquid comes out. This post on what drives flow rate accuracy tells you why.
Where Does Uninterrupted Dosing Matter Most?
Nonstop dosing matters most in five fields: precision spraying, cell culture, drug delivery, chemical synthesis, and food additives. DK Infusetek says all five need an exact flow that does not stop.
Syringe Pump for Microfluidics Research
A syringe pump for microfluidics has to feed tiny chips at an even rate. If the flow stops, the drops in the chip can change size. A continuous flow syringe pump keeps the liquid moving, so there is no stop to refill.
Flow Chemistry Syringe Pump Applications
A flow chemistry syringe pump sends chemicals into a reactor at a set speed. When the flow stays steady, the mix stays the same. With RS485 and Modbus RTU, the pump can also connect to a bigger control system.
Coating, Spraying and Dispensing Lines
Coating and spraying lines use the dispensing mode to give out set amounts. Some liquids carry hard bits that wear out soft valves. For these, a strong ceramic valve lasts longer.
How to Pick a Constant Flow Syringe Pump
The right constant flow syringe pump matches your liquid in syringe size, pressure, and valve. It also fits the way you run your work. Go through these four checks in order.
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Match the flow to the syringe: For a low flow syringe pump, use a small syringe. A 50 μL syringe can go as low as 0.0625 μL/min.
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Check the pressure: The normal limit is 0.68 MPa. If you need more, ask DK Infusetek what it can offer.
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Pick the right valve: Hard bits like graphene or carbon powder wear down PTFE valves fast. DK Infusetek made its alumina 3-port ceramic valve to solve this. It fits the CFSP-I. But it only handles up to 0.4 MPa, which is less than the pump's 0.68 MPa.
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Plan how you will run and care for it: Both models can be started and stopped by outside 5–24V signals. This helps a flow chemistry syringe pump work with other machines. Built-in counters track how much the valve and syringe are used, so you know when to service them. For cold work, use low-temperature syringes.
Inside DK Infusetek's Micro-Fluid Focus
DK Infusetek designs, builds, and customizes syringe pumps. These pumps move very small amounts of liquid. The head office and R&D center are in Shanghai. The factory is in northern China.
Its website sells only syringe pumps and pump parts. Its own R&D team built its continuous flow syringe pump line. You can download spec sheets and watch a setup video on the product pages. When you ask for a price, also ask about delivery time and certificates. Learn more in DK Infusetek's company profile.
FAQs
Can the Pump Be Controlled From a PC?
Yes, you can run both models from a PC. They connect through RS232 or RS485 with Modbus RTU.
Outside 5–24V signals can start, pause, and stop the pump.
A signal output shows when liquid is flowing.
Which Syringes Fit a Continuous Syringe Pump?
The pump takes nine syringe sizes, from 50 μL to 25 mL. Each one has a borosilicate glass barrel, a stainless steel plunger rod, and a PTFE seal.
Pick the size that fits your flow rate.
For cold work, use low-temperature syringes.
How High Can Liquid Path Pressure Go?
The normal limit is 0.68 MPa on both models. If you need more, ask the maker.
CFSP-I/CU-I: contact DK Infusetek.
CFCU-I: an upgrade is available.
What Valve Materials Can You Choose?
The CFSP-I/CU-I valve is made of PCTFE and PTFE. The CFCU-I lets you choose ceramic, PTFE, or PEEK. Ceramic is best for liquids with hard bits in them.
The ceramic valve handles up to 0.4 MPa.
It works from 0°C to 100°C.
Conclusion
Choose the CFSP-I/CU-I if you want a touch screen controller for several pump units. Choose the CFCU-I if you want everything in one unit with more valve choices. Each one works well as a precision syringe pump for microfluidics, chemistry, or dosing.
Duko Industrial Technology (Shanghai) Co., Ltd., also called DK Infusetek, focuses on moving very small amounts of liquid. Do you need a continuous flow syringe pump for your work? Contact the DK Infusetek team. Tell them your liquid, flow range, and pressure.