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How to Select the Right Piston for Your Fluid

A Helpful Guide on Selecting the Best Syringe Barrel Piston for the Fluid You’re Dispensing

28 June 2019

By Tom Muccino

Whether you’re dispensing a standard grease, stringy RTV, particle-filled solder paste, or thin cyanoacrylate, knowing which type of syringe barrel piston is best for your fluid can eliminate a lot of headaches later in production.

At Nordson EFD, we offer six types of Optimum® syringe barrel pistons, each with unique features to deliver the best possible dispensing results for your fluid and application requirements. Here’s more information about how each style can improve your manufacturing process.

General Purpose Pistons

Our white SmoothFlow pistons are used for most dispensing applications because they work exceptionally well with the widest range of fluids.

This piston is designed to provide the perfect interference fit between the outer diameter of its double wiping edges and the inner diameter of the syringe barrel. As you dispense, its precision wiping edges sweep along the inside diameter of the barrel, wiping the walls clean and eliminating fluid waste.

3 Options to Prevent Piston Bounce

When air gets trapped below the piston causing it to separate from the fluid it is known as piston bounce. This can lead to oozing and drooling after the dispense cycle.

Choosing the right piston can help prevent piston bounce. EFD provides three options.

  1. Orange Flatwall pistons work best for thick, stringy fluids like RTVs. They are designed to have a negative interference fit where the walls of the piston do not contact the inside walls of the syringe. Having more room between the piston and barrel wall prevents air from getting trapped under the piston.

  2. Beige SmoothFlow pistons are an alternative to orange pistons when the fluid you’re working with is very expensive. These have a slightly tighter fit than the orange pistons and have a double wiper design similar to our white SmoothFlow pistons. The wipers reduce the amount of waste in a syringe, which reduces costs when working with expensive assembly fluids.

  3. Clear Flex pistons work best when dispensing very thick or particle-filled materials at extremely high pressures and high cycle rates. Since these materials require numerous air pressure pulses to dispense small amounts, this can cause air entrapment. Engineered to flex with each deposit to create a tighter seal as air pulses, the Clear Flex piston prevents air from getting pushed past the wipers. The leading wiper blocks air, acting like a secondary seal for accurate, consistent deposits every time. Watch video.

Barrier Pistons for Thin Fluids and CAs

Our blue LV Barrier pistons are the perfect solution for watery fluids and low-viscosity cyanoacrylates (CAs). This is our tightest fitting piston. It stays in place instead of traveling down the barrel while you’re dispensing. This prevents instant adhesives from bonding to the syringe. A small hole in the piston allows air to pass through and pressurize the fluid to make a deposit. Watch video.

Pistons for Mechanical Dispensing

Red SmoothFlow pistons are designed for use with manual or mechanical dispensers. Designed with a positive interference fit, this tight-fitting piston can accommodate the force of mechanical dispensers.

Overall, choosing the right piston for your application improves process control. It helps reduce costs by reducing material waste, and prevents downtime caused by rework and rejects associated with inconsistent dispensing.

Need more info about dispensing best practices? Don’t hesitate to contact us at info@nordsonefd.com. For details about EFD’s Optimum dispensing component systems, download this guide.

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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