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How to Prevent Air Bubbles from Causing Piston Bounce

A Deep Dive into Piston Bounce Causes and Cures

10 December 2019

By Tom Muccino

Piston “bounce” is one of the most common issues that can affect your dispensing repeatability. This occurs when the piston separates from the fluid inside a syringe barrel.

The most common causes of piston bounce are:

    • improperly installed pistons
    • air bubbles in your fluid
    • frozen fluid that’s not thawed properly
    • high-speed dispensing of thick paste

    In this article, we will dive into each of these causes of piston bounce and explain how to prevent them.

    Proper Installation of Pistons

    As we mentioned in a previous article, How Pistons Improve Your Dispensing Process, pistons can be extremely useful in your manufacturing process. The key is to ensure that your setup is correct prior to dispensing.

    When installing your piston manually, you are going to feel some resistance or back pressure as you’re pushing the piston down into the syringe. This pressure is caused by air that’s trapped between the piston and fluid. An easy workaround is to gently squeeze the sides of the syringe so the air can escape and you can get the piston in the proper position.

    See more tips in this brief video.

    Note that if you’re bottom filling a syringe with most types of fluid, we recommend using our white SmoothFlow piston. Its design allows air bubbles to rise and escape, leaving you with an air-free syringe.

    Eliminating Air Bubbles

    Air bubbles are fairly common, even if you get your syringes pre-packaged, because changes in pressure and vibration during shipping can cause air bubbles to form. These bubbles will then expand and contract, forming even larger air pockets, which can result in piston bounce.

    One way to eliminate air bubbles is to degas medium- to high-viscosity fluids with a centrifuge. You can simply put your syringe inside the centrifuge and run it according to the instructions.

    Another way to get rid of air bubbles is to stand the barrels up tip end down and let the fluid settle for about 24 hours. Note that this method only works with low- to medium- viscosity fluids. After 24 hours, the air bubbles will have risen to the top and you can simply squeeze the sides of the barrels and gently push the piston down to meet the fluid line.

    Working with Frozen Fluids

    When working with frozen fluids, it’s important to remember that frozen fluid thaws at a different rate than frozen plastic packaging. There is no way to rush this process. You should carefully follow the manufacturers’ thawing instructions to avoid forming air bubbles, also known as freeze thaw voids (FTVs), when improper thawing methods are used.

    High-Speed Dispensing with Thick Paste

    Dispensing thick pastes from small dispense tips at high cycle rates can create the perfect environment for air to form under a piston. To avoid this, we recommend using our Optimum Clear Flex pistons, which are designed for this specific purpose.

    In conclusion, the best ways to prevent piston bounce are to install your piston properly, use a centrifuge or stand a syringe up and let it sit for 24 hours to get rid of air bubbles, thaw frozen materials based on manufacturers’ specifications, and use the right kind of piston when working with thick pastes at high cycle rates.

    Have a question about piston bounce? Don’t hesitate to request expert advice by contacting us at today!


    Tom MuccinoAbout Tom Muccino

    Tom Muccino is a Regional Sales Manager at Nordson EFD. He manages the sales team located in the Midwest to the West Coast of the U.S. and Canada. Tom has more than 30 years of fluid dispensing expertise. He joined Nordson EFD in 1987.

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