Piston Fillers

Acasi Machinery Piston Fillers - Discover the mechanics and versatility of volumetric piston filling machines, ideal for a wide range of product types and container sizes.

What is a Piston Filler and How Does it Work?

Volumetric piston fillers are filling machines that pull products from a bulk supply tank or vessel into a specific cylinder size and then discharge that amount into the container. The piston and cylinder are like a syringe that is used in the medical field. Piston fillers are simple machines that are composed of an open cylinder with a piston and valves on the other end. The valves work in opposite directions to allow the product to move in only one direction depending on the movement of the piston within the cylinder. The product moves into the cylinder with the draw stroke while the discharge stroke pushes the product out.

The total amount of product that can be filled in a single cycle is determined by the diameter of the cylinder and the stroke of the piston inside it. The amount of product that the cylinder dispenses is adjustable by changing the stroke length, a longer stroke for more product and less with a shorter stroke. Stroke length is adjustable by mechanical or control panel changes while cylinder diameter is only changed by swapping to another size. Valving for the cylinder will vary depending on the range of products the machine is designed for. Any thicker, very thick, products with particles or pieces will use rotary valves that can open wide to allow these to pass freely. Lower viscosity or thinner products can use check valves that have smaller openings that do not require separate activation to operate.

Piston Filling Product types

Piston filling machines are designed to work with a very wide range of liquids from low to high viscosity including soft particles or pieces up to ¾” or 19mm in diameter. The range they excel within is the middle to higher thickness range. If your product range is only those that are thinner, other machines have a lower investment requirement. Examples of the mid to high range are edible oils, sauces, creams, gels, or any product that does not pour quickly out of a bottle or has particles or pieces in it.

Hot-filled products can also be challenging due to the swelling of the cylinder and piston components from the heat. A machine designed for high-heat products will have a tougher time running a thinner product at room temperature due to the design of the machine for swelling.

Piston Filler - Operating speeds

Piston filling machines can run very fast. The speed will vary depending on what the product is like and the size of the fill. Larger fill sizes and thicker products will usually run slower. Typical speeds of piston filling machines are 10 containers per minute per head on the machine. So, a 4-head filler can typically run at 40 per minute depending on the amount filled and how the product handles. Piston fillers are available in single-head semi-automatic machines and automatic machines from 2 to 14 heads depending on the size of the fill and machine platform.

Different piston filling drive systems can also have an effect on the speed as well as the accuracy of the dispensed amount. The different drive systems are pneumatic (air), air over oil, and servo (electric). Air-based systems are more economical and have a limited range of control for their intake and discharge speeds. They are also dependent on the amount of compressed air available to them within the plant where they are installed. Large machines of this type can require large amounts of compressed air which can mean upgrades or replacements for the compressed air system in the facility. Air over oil systems also use large amounts of compressed air though they run much more consistent with the smoothing effect of the oil to reduce the changes that happen in the air supply.

Servo piston filling systems are certainly the best choice as they have an almost unlimited ability to control all speed ranges for the intake and discharge of products as well as less need for compressed air. The accuracy of servo operation surpasses that of pretty much every air system and provides quick volume changes from the control panel instead of time-consuming mechanical stroke adjustments.

Piston Filling Machine - Container Sizes

Piston filling machines are designed to work within a fill size range for a specific set of piston and cylinder combinations. The range for a specific set is usually 10:1 for the general rule though some very cheap imported equipment is limited to 8:1 due to less rigid manufacturing standards. So, if you have a set of 1-liter (34 oz.) pistons and cylinders, the lower end of the fill size range is 100ml (3.4 oz.). The actual amount varies depending on product properties.

The upper end of the fill size range for a specific set of pistons and cylinders can also be changed by using multiple strokes of the piston to get a larger fill. Great care must be used with this operation to prevent “stacking error” from slight differences that add up in the fill volume during set-up that results in an over or under-fill situation. The accuracy of the servo system helps prevent this issue by helping the operators set up more easily.

Cleaning Piston Fillers

Whether you are running a food product or something that does not have the same level of sanitary requirements, cleaning the fluid path is the biggest challenge for a piston filling machine. The only way to do this well is to take the fluid path apart and clean it out by hand. Having a machine that allows for this task to be completed with as little disassembly as possible is the best choice to prevent lost or mixed-up parts that create obstacles to your next production run. Using parts that are well suited to cleaning such as stainless steel, Teflon, and other FDA-approved materials also aids the process.