General information on back pressure in a syringe

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Discussion Overview

The discussion centers on the concept of "back pressure" in syringes, particularly focusing on the behavior of a syringe filled with air when the plunger is depressed and then released. Participants seek to understand the underlying principles and seek resources for further reading.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant inquires about the difference in behavior between syringes filled with air versus those filled with water.
  • Another participant describes a scenario involving a syringe filled with air connected to an empty syringe, seeking resources to understand the phenomenon without needing a solution.
  • A participant explains that air is compressible, noting that when pressure is increased, the volume decreases, which causes the air to exert back pressure. They reference Boyle's law as a relevant principle.
  • Another participant suggests looking into the concept of "hysteresis" and points out the importance of specifying the seal type in the syringe.

Areas of Agreement / Disagreement

Participants express varying inquiries and perspectives regarding back pressure, but there is no consensus on a singular explanation or resource. Multiple viewpoints and questions remain unresolved.

Contextual Notes

The discussion does not clarify the assumptions regarding the types of syringes or the specific conditions under which the observations are made. There is also a lack of detail on the seal types mentioned.

Who May Find This Useful

Individuals interested in fluid dynamics, syringe mechanics, or those seeking foundational knowledge in physics related to pressure and volume relationships may find this discussion relevant.

Petra de Ruyter
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Hi all

I'm looking for general information on "back pressure" specially in a syringe. So when you put your finger over the top of a syringe and depress the plunger then release the pressure on the plunger and the plunger moves back slightly. I'm struggling to find some specific information that will help me explain this scenario? So any reading that you think would be good please provide a link.

Cheers
 
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Hello Petra,

Did you notice a difference between syringes filled with air as opposed to syringes filled with water ?
 
This syringe is filled with air only and connected to another syringe that is empty. I'm looking for a text reading that will help me understand what is happening, I don't necessary need anything solved just need a good resource that I can refer to.
 
Air is compressible: when you increase the pressure (push down the syringe) the volume decreases. The air in the reduced volume presses back.
When all this is done at approximately the same temperature, the product of air volume (in the two syringes combined) and pressure is constant (Boyle-Gay Lussac law). Google or look it up in an introductory physics textbook.
 
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Also, Google "hysteresis." You haven't identified/specified seal type.
 
Many thanks to all that have posted.
 

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