A diaphragm pump is a type of positive displacement pump that uses a flexible membrane to move and pressurize a fluid. This mechanism works by repeatedly enclosing a fixed volume of fluid and mechanically moving it through a system, making it suitable for low-to-moderate capacity and pressure applications. The pump transfers a wide variety of liquids, gases, and slurries using a reciprocating action to create the pumping force. This design allows the pump to handle diverse media, including viscous or abrasive materials, while keeping the drive mechanism sealed off from the fluid.
What is a Diaphragm Pump
The diaphragm is a flexible barrier, typically made from materials like rubber, thermoplastic, or Polytetrafluoroethylene (PTFE), chosen for chemical resistance and durability. It separates the working mechanism, such as air or hydraulic fluid, from the process fluid being pumped. This separation prevents contamination of the fluid and protects the pump’s mechanical parts from corrosive or hazardous media.
The main components also include a pumping chamber, which expands and contracts with the diaphragm’s movement, and a housing that contains the assembly. The pump relies on a pair of non-return valves, known as check valves, situated at the inlet and outlet ports. These one-way valves open and close based on pressure differences, controlling the flow of fluid into and out of the chamber.
How the Pumping Cycle Works
The fluid transfer operates on a two-stroke, reciprocating cycle: the suction stroke and the discharge stroke. The suction stroke begins when the diaphragm moves away from the pumping chamber, causing the volume to increase. This expansion creates a pressure drop inside the chamber below the fluid source pressure, forcing the inlet check valve to open and drawing fluid into the pump chamber.
The movement then reverses, initiating the discharge stroke. The diaphragm moves inward, rapidly decreasing the volume and compressing the fluid. This pressure increase forces the inlet check valve to close, while concurrently opening the outlet check valve, expelling the fixed volume of fluid into the discharge line. This alternating movement results in the steady, albeit pulsating, flow of fluid through the system.
Different Power Sources
Diaphragm pumps are categorized by the mechanism used to actuate the diaphragm, with three major power sources determining their operational characteristics.
Air-Operated Double Diaphragm (AODD) Pumps
AODD pumps use compressed air, directed by an internal air valve, to alternately apply pressure to the back of two diaphragms connected by a common shaft. This reliance on compressed air makes AODD pumps intrinsically safe for use in volatile or explosive environments, as they require no electrical motors that could produce a spark. They are highly portable and capable of running dry without damage, although their energy efficiency can be lower due to the power required for the compressed air system.
Mechanically Actuated Pumps
These pumps, sometimes called electric diaphragm pumps, are driven by an electric motor that transmits motion to the diaphragm via a mechanical linkage, such as a crankshaft. This design offers greater energy efficiency and precise control over flow rates, making them a popular choice for continuous duty applications like chemical dosing or metering. Since they do not require a separate compressor, they are better suited for locations where a stable electrical supply is available.
Hydraulically Actuated Pumps
This type employs hydraulic fluid pressure transferred by a piston to move the diaphragm. These pumps are preferred for applications demanding very high pressure capabilities or accurate dosing and metering, often found in the oil and gas industry. The hydraulic fluid acts as a buffer, cushioning the diaphragm and allowing the pump to generate high discharge pressures while maintaining smooth operation.
Versatile Uses Across Industries
The design of diaphragm pumps, which isolates the fluid from the working parts, makes them versatile for handling challenging media across numerous industrial sectors.
In chemical processing, they safely transfer aggressive substances like acids, solvents, and reactive chemicals without the risk of leakage or corrosion due to non-metallic component options. This sealing advantage is also used in the pharmaceutical industry for sterile transfer and accurate dosing of sensitive products like vaccines and biological samples.
Diaphragm pumps are also widely used in the food and beverage sector because they can be constructed with hygienic, FDA-compliant materials. They are gentle enough to handle viscous liquids like syrups, oils, and dairy products without compromising product integrity.
Their ability to pump abrasive slurries with high solids content without clogging makes them suitable for demanding tasks in wastewater treatment, mining, and construction. In these applications, they are routinely used for dewatering and for dosing treatment chemicals like chlorine and sodium hydroxide.