What Is a Syringe Pump?
A syringe pump is made up of a precision linear drive for aspirating and dispensing discrete volumes of fluid or gas by actuating a syringe. In most cases, there is also a rotary valve driver that can actuate a valve to direct flow through specific ports for aspirate and dispense. The syringe pump is often integrated into a larger clinical or analytical instrument, as a critical component for metering and directing fluid.
Pros & Cons of Syringe Pumps
Advantages of Syringe Pumps
Syringe pumps are great for aspirating and dispensing discrete volumes of fluid. Because there are multiple syringe volumes and pump resolutions, there is a wide range of dispense volumes and dispense speeds available. This combination of precision syringes and syringe pumps provide very accurate and repeatable dispense volumes.
Disadvantages of Syringe Pumps
Syringe pumps are not good for continuous flow applications. Because a syringe has a maximum volume, it will have to refill to dispense any volumes greater than its maximum volume. Syringe pumps are typically large to accommodate a fully aspirated syringe plus the motors that drive the syringe and valve.
Types of Syringes
Gastight Syringes
Gastight syringes are capable of aspirating and dispensing liquids, as well as gasses. Gastight syringes are preferred when there is concern regarding carryover from one cycle to the next and/or cross-contamination. Gastight syringes limit the amount of carryover from one dispense to the next aspirate by using a dynamic seal that travels towards the zero end of the syringe as it dispenses. This configuration leaves minimal amount of fluid, known as carryover, between cycles. Carryover can further be reduced by using ZDV (Zero-Dead-Volume) gastight syringes.
Gastight syringes can be susceptible to damage by particulate in the fluid/media, which can result in shorter life when compared with positive displacement syringes.
Zero Dead Volume (ZDV) Syringes
Zero Dead Volume (ZDV) syringes are gastight syringes that reduce carryover volume between dispense and aspirate moves. ZDV syringes are gastight syringes with an extension on the plunger tip that protrudes into the end cap orifice when fully dispensed. There can be matching tapers between the plunger tip and end cap that aids in expelling air bubbles that would otherwise be trapped in the syringe. Also, the ZDV option reduces carryover volume between dispense and aspirate moves.
In applications that are sensitive to flow variation, when the plunger tip extension enters the end cap, the flow will be affected by the reduction in orifice.
Liquid Tight Syringes
Liquid tight syringes aspirate and dispense fluid but are not gas tight. They are syringes with stainless steel, glass, or ceramic plunger rods hand-fit to the glass barrel. These syringes will perform like displacement syringes but are not gas tight. They are best suited for manually dispensing small volumes where the fluid is compatible with the stainless-steel plunger.
Static Seal/Positive Displacement Syringes
Positive displacement syringes have a static seal near the aspirate end of the syringe and fluid is controlled by the volume displaced by the plunger rod actuation. Positive displacement syringes can offer better precision and accuracy over standard piston syringes. They are also better with media that contains particulate. This typically results in longer life because of a more robust seal configuration.
However, they typically have larger amount of carryover and higher chance of cross-contamination. They can also have higher drag force due to their robust seal configuration.
Low Temperature Syringes
Low temperature syringes perform as gas tight syringes in an environment that is colder than the standard operating environment. They are designed to meet standard performance requirements at lower temperatures. When a standard syringe is subjected to lower temperatures, it will typically leak or function at a reduced pressure because of material thermal properties.
Backfill Syringes
Backfill syringes, also known as backflush, have an orifice through the plunger assembly that allows the syringe to be filled from an external source without actuating the syringe piston. They can be rinsed with a buffer solution between dispense cycles. In order to direct flow through the end cap orifice or plunger assembly orifice, external valving is needed to control flow direction.
Applications Best Suited for Reinforced Syringe Plungers
Applications that require extremely small dispense volumes would benefit from reinforced syringe plungers. Because of their small volume, they have very small diameter plunger rods that may bend easily if not supported or reinforced.
Ready to get started? Find the best type of syringe for your application
Materials’ properties and their operational conditions contribute toward success or failure of a given application in its indented environment.
Leave a comment!