The Precision Power of Bent-Axis Filling Pumps

Sometimes you need to precisely dispense or fill liquids in extremely small quantities. Fill volumes can range from a few milliliters down to a few dozen microliters. The typical piston filler is difficult to control precisely at these volumes.

Bent-axis pumps convert the rotary motion of a servomotor to reciprocating linear motion without using a crank. They get their name because the axis of the motor is bent in relation to the axis of the piston. The piston rod is held in a ball-socket coupling with a drive pin attached to the motor. The pump is mounted on a plate that can be angled relative to the motor shaft. When the piston is in a straight line with the motor shaft, it rotates with no linear motion. When angled, the rotation of the motor causes both rotary and linear movement of the piston.

John R. Henry / Changeover.com

Bent-axis filling pump

Bent-axis pumps often combine the piston and inlet/discharge valves. The piston has a flat on it. As it rotates, it opens and closes the infeed and discharge ports.

John R. Henry / Changeover.com

Rotating piston with valve

This eliminates the need for separate valves, as well as the mechanism to drive them.

The linear travel is adjusted by changing the angle of the pump to the motor. More angle equals more linear travel and more product dispensed. A micrometer screw, not shown, adjusts the angle precisely and repeatably.

The nature of the drive limits the length of the pump stroke. This may require several strokes to achieve the desired fill volume. This improves fill precision as the multiple strokes tend to cancel out any variations in the individual strokes.

Pump heads, piston, and cylinder may be made from stainless steel or any other suitable material. Ceramic is frequently used for better durability. Tight manufacturing tolerances eliminate the need for seals.

This article was adapted from Chapter 4 Volumetric Filling – Piston Fillers of John Henry’s new book Secrets of Liquid Filling. This book will teach you more than you will ever need to know about filling any kind of liquid in any kind of container.

Full details and chapter samples are available at www.packmachbook.com.

Purchase the book on Amazon here.