Diaphragm pumps: How they work, applications, and an example of miniaturization

Medical devices, analytical instruments, and manufacturing systems require precise and clean transport of liquids and gases. Diaphragm pumps are able to meet such high standards for delicate fluid handling.

Diaphragm pumps are incorporated into cell analyzers, 3D printers, and industrial printers, serving fields that range from life sciences to advanced manufacturing processes.

To benefit fully from their performance capabilities, it is essential to understand how they work, their features, and how to select equipment most suited for the application.

This article covers the operating principles, features, types, and applications of diaphragm pumps. Important points to keep in mind during selection and use, as well as Orbray's own design examples, are also presented.

What is a Diaphragm Pump?

A diaphragm pump uses an elastic membrane, called a diaphragm, to change the volume of the pump chamber to draw in and expel liquids or gases. A biological example of a diaphragm is the thin sheet of muscle in the chest that flexes to move air through the lungs.

A diaphragm pump has a simple structure, is easy to use, and can transport fluids without altering their properties. For these reasons, diaphragm pumps are used across a wide range of fields, including medicine, life sciences, and advanced manufacturing.

How Diaphragm Pumps Work

A diaphragm pump moves fluid in a single direction through the reciprocating motion of the diaphragm, and the opening and closing of two check valves. Flow is produced by the repetition of two cycles: suction and discharge.

In the suction cycle, the diaphragm is pulled back and the volume of the pump chamber expands, lowering the internal pressure. The suction-side check valve opens while the discharge-side check valve remains closed. As a result, fluid is drawn into the pump chamber.

In the discharge cycle, the diaphragm is pushed forward and the volume of the pump chamber decreases. This raises the internal pressure. The discharge-side check valve opens, the suction-side check valve closes, and the fluid is pushed out. Various drive mechanisms are used to move the diaphragm, including air, hydraulic, motor, and solenoid systems.

Because the diaphragm pump alternates between suction and discharge, the flow rate fluctuates in a pulse-like pattern. This is called pulsation.

The diaphragm pumps developed by Orbray convert the rotational motion of a motor into the linear motion of the diaphragm using an eccentric crank. They are used in applications such as medical equipment and analytical instruments, where precise fluid delivery is required in very confined spaces.

For detailed specifications and features, please refer to the product page below.

　

Characteristics of Diaphragm Pumps

An important feature of the diaphragm pump is that it preserves the cleanliness of the fluid being transported.

The diaphragm pump moves liquid and gas by deforming the membrane surface. It differs in design from other reciprocating pumps, such as piston pumps. In piston pumps, sliding parts (the piston within the cylinder) come into contact with the fluid being pumped. Lubrication of those parts, and wear and tear between the parts can contaminate the fluid being pumped. The diaphragm pump has no sliding or moving parts in the wetted section, eliminating the danger of lubricant or wear particles contaminating the fluid, thereby maintaining the cleanliness of the fluid.

Another advantage is the low risk of fluid leaking out of the flow path through sliding parts. Because external leakage is unlikely to occur, the diaphragm pump improves safety in applications involving chemicals or highly volatile solvents.

Types of Pumps

Pumps are categorized based on how they work and their structures. Broadly, they are categorized as positive displacement pumps and non-positive displacement pumps.

Diaphragm pumps are positive displacement pumps.

Positive Displacement Pumps

A positive displacement pump moves fluid by expanding an internal space to draw fluid in, then contracting that space to push it out. Types include those that use the reciprocating motion of pistons or plungers, and those that use the rotational motion of gears or screws. Diaphragm pumps are a type of positive displacement pump.

Because these pumps push out fluid in fixed volumes, they can maintain consistent delivery, offering excellent flow accuracy. Some designs even provide their own suction capability, allowing them to start operation without needing priming first.

Non-Positive Displacement Pumps

A non-positive displacement pump moves fluid by rotating an impeller at high speed, using centrifugal force or fluid momentum to expel the fluid. Representative examples include centrifugal (volute) pumps and axial-flow pumps.

Unlike positive displacement pumps, they can deliver large volumes of fluid continuously, making them suitable for applications with high flow-rate requirements, such as water supply, sewage, and drainage. On the other hand, they generally require priming before operation, and the delivered volume tends to fluctuate with upstream pressure.

Applications of Diaphragm Pumps

Diaphragm pumps are used in cell analyzers, 3D printers, industrial printers, and other equipment, serving a wide range of fields from life sciences to advanced manufacturing processes.

Cell Analyzers

In cell analyzers, individual cells within a sample must be lined up and arranged so that they can be examined and characterized. This requires a fluidic system that reliably transports samples and reagents in a very controlled way. For example, in flow cytometers, diaphragm pumps are used not only for sample injection, but also for the delivery of reagents, cleaning fluids, and waste liquids.

Preserving analytical accuracy requires minimizing the introduction of foreign matter. The membrane of the diaphragm pump separates the fluid from the drive components. This prevents contamination of the fluid. Selecting wetted components matched to the fluid also allows the pump to handle a variety of reagents.

3D Printers

In 3D printers, diaphragm pumps are used to continuously deliver liquid resin to the print head. In systems that handle photocurable resins and other liquid materials, the pump supplies the material steadily from the resin tank to the print head.

A diaphragm pump is chosen for this application for two reasons: the flow accuracy needed to deliver fixed volumes precisely, and the flexibility to accommodate specialized resins through wetted-part material selection. Consistent supply directly contributes to quality of the finished part.

Industrial Printers

In industrial printers, diaphragm pumps are used as ink circulation pumps that supply and circulate ink consistently. They are particularly effective in large-format industrial inkjet printers. Their purpose is to prevent settling of high-density pigments, remove air bubbles, and reduce nozzle drying and clogging.

Tube pumps are also used for fluid delivery, but they require periodic replacement because their structure squeezes the tube. Diaphragm pumps, by contrast, can circulate ink without contaminating it, and require less maintenance.

Points to Keep in Mind When Using Diaphragm Pumps

Issues such as "diaphragm pumps not drawing fluid as expected" or "short lifespans" often trace to a few common causes. To maintain performance over the long term, four key points are worth understanding.

Foreign Matter Reduces Performance

The diaphragm pump depends on the check valves opening and closing in coordination with diaphragm movement to alternate between suction and discharge. If debris accumulates around the valves and impedes their function, the pump loses the ability to draw in or discharge fluid correctly. Special caution is required after running fluids other than purified water. Leaving the pump idle while filled with such fluids can cause solid components in the fluid to harden and adhere to the valves, affecting performance.

Reduced Sealing Tightness Reduces Pump Performance

Pump performance also declines when a check valve no longer seals tightly against its valve seat. A proper seal stops fluid from leaking past the valve and flowing in the wrong direction.

When this seat contact is damaged, fluid can flow backward or leak, preventing the pump from performing its intended function of delivering a precise flow. Because the diaphragm pump depends on its check valves, precision in the valves is essential to maintaining stable self-priming and consistent flow.

Specialized Materials May Be Required for Certain Fluids

Depending on the fluid being transferred, special materials with high chemical resistance may be required. Chemical resistance refers to the property of resisting deterioration when exposed to chemicals. For example, some inks used in inkjet printers can degrade rubber materials inside the pump.

To obviate such problems, Orbray offers high-chemical-resistance specifications using materials such as FFKM (perfluoroelastomer), which provides extremely high chemical resistance, and has a track record of adoption in related fields.

Overpressure Can Lead to Damage

If the discharge-side pressure becomes abnormally high, damage to the pump or piping can occur. Pressure builds easily because the diaphragm pump operates by increasing pump chamber pressure to expel fluid.

If the discharge-side piping becomes blocked, resulting in what is called deadheading, pressure will continue to rise until it reaches the limit of the drive mechanism. To prevent accidents, systems require safety valves that relieve pressure, or safety switches that detect overload and stop the pump.

Diaphragm Pump Implementation Examples

Two examples of diaphragm pumps delivered by Orbray are explored below. In each case, specifications were optimized to meet the specific requirements of the customer.

High Chemical Resistance while Maintaining High Integrity of the Fluid

The first example is of diaphragm pumps for industrial inkjet printers, which require pumps that supply ink continuously and consistently. Orbray met an interesting challenge with these printers.

Inks vary widely. They can be water-based, organic solvent-based, or UV-curable types. Depending on ink type and color, some inks aggressively attack the rubber materials used in the moving components such as valves and diaphragms. Testing showed that even the fluororubber used in our relatively chemical-resistant standard products showed degradation when used in industrial inkjet printers, and could not consistently deliver adequate service life.

To address this, Orbray provided wetted-part test specimens and worked through the requirements verification process with our customer. As ink formulations are proprietary to the printer manufacturer, and chemical resistance can vary even within the same rubber category depending on the formulation, verification with the actual ink in use was essential. After repeated testing, Orbray was able to establish the required durability using high-chemical-resistance specifications built on FFKM (perfluoroelastomer), together with components treated with PTFE coating.

Beyond degradation, we also encountered cases where the additives used in the rubber itself adversely affected the ink. In one such case, analysis correctly identified rubber additives as the cause of contamination. Switching to a different rubber material resolved the issue.

38% Reduction in Pump Length with Doubled Service Life

The second case involved the miniaturization of a pump for portable medical equipment. The customer had already adopted an Orbray pump in the previous model of the medical device, but further device miniaturization required a smaller pump.

In the new device, the pump had to be smaller and lighter while largely maintaining the same performance characteristics, including flow rate. Low vibration and low noise performance also needed to be preserved. Power consumption was to be reduced, and replacement interval needed to be doubled. Meeting all of these requirements simultaneously was technically demanding.

An overseas manufacturer evaluated in parallel could not meet the requirements. Miniaturization increases the load on individual components, negatively affecting service life, vibration, and noise performance.

Orbray started with a flat brushless motor as the base, which allowed for a substantial reduction in overall length. To address the higher component loads, Orbray combined several techniques. Structural load simulation guided the design. Lubricant selection was verified. Sliding surfaces were analyzed using Orbray's proprietary Optical Inner Wall Metrology System. By combining these methods, the service life requirement was achieved. Vibration and noise were tuned through repeated prototyping. Power consumption was reduced through optimization of motor parameters.

The final result was a 38% reduction in overall pump length and a doubled replacement interval. Achieving this depth of engineering is difficult for pump manufacturers that procure motors from external suppliers. In-house motor development was the pivotal factor in achieving our outstanding result.

Conclusion: Select a Diaphragm Pump Based on the Characteristics of the Fluid Being Delivered

The diaphragm pump is a positive displacement pump that moves fluid through membrane motion and check valves. Because it preserves fluid cleanliness and delivers excellent flow accuracy, it is used across a wide range of fields, including cell analyzers and various types of printer applications.

To maintain stable performance, however, attention must be paid to the condition of the check valves. Prevention of overpressure must also be considered. Most important is selecting wetted-part materials and specifications appropriate to the characteristics of the fluid being delivered.

Orbray develops and manufactures compact, lightweight, chemical-resistant diaphragm pumps built around its in-house high-efficiency motors. We also offer high-chemical-resistance specifications using FFKM, along with custom solutions, to propose the optimal pump for each fluid and equipment application.

For product details, please refer to the diaphragm pump product page below.