Piston pumps and diaphragm pumps are used for similar applications, particularly agricultural spraying. However, there are many important differences between these types of pumps to consider before making a purchase. By choosing the best pump for your specific task, you can extend the service life of your pump and ensure superior performance. Below, we’ll discuss the key factors you should evaluate before buying a diaphragm or piston pump.
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What’s the Difference Between Diaphragm Pumps & Piston Pumps?
Diaphragm pumps and piston pumps are both positive displacement pumps, but they differ in how they operate. In a diaphragm pump, a flexible membrane (diaphragm) expands and contracts, creating an air vacuum that draws fluid into the pump via an inlet valve, then expels it through an outlet valve. In a piston pump (also known as a check valve pump), a piston moves up and down inside one or more cylindrical chambers. As the piston retracts, it pulls fluid into the cylinder, which is then pushed out when the piston extends. Check valves are used to control the flow of liquid.
Advantages and Limitations of Diaphragm Pumps & Piston Pumps
Diaphragm pumps and piston pumps are both excellent choices for spraying and liquid transfer applications, but they differ in their capabilities. While both pumps can deliver excellent flow rates, diaphragm pumps offer enhanced durability, particularly when handling corrosive or abrasive liquids. Piston pumps, on the other hand, deliver more consistent pressure and performance. Some pros and cons of each type of pump are outlined below:
Diaphragm Pump
Advantages
–Versatility. Diaphragm pumps can handle a wide range of fluids, including corrosive and abrasive liquids.
–Convenience. Diaphragm pumps are fully self-priming and do not require frequent lubrication.
–Durability. Diaphragm pumps can be run dry without sustaining damage. They’re also more tolerant of mishandling than piston pumps and require less maintenance.
–Safety Features. Diaphragm pumps have a lower risk of leaks and product contamination.
Limitations
-Reduced efficiency.
-Less consistent flow rate.
-Less suitable for high-pressure applications. Under high pressures, the flexible components of a diaphragm pump can rupture.
Piston Pump
Advantages
–Precision. Piston pumps allow precise control over flow rates.
–Superior performance. Piston pumps deliver a more consistent flow rate and they’re suitable for high-pressure applications.
–Continuous operation.
Limitations
-Susceptible to damage from abrasive or corrosive liquids.
-Frequent lubrication is required to reduce wear on the pistons.
-Cannot be run dry.
-Prone to leakage during operation.
What to Consider When Choosing a Pump
In addition to understanding the advantages and limitations of piston pumps and diaphragm pumps, you should always review any job-specific requirements before purchasing a pump. Several criteria to consider when selecting a piston or diaphragm pump include:
1. Chemical compatibility.
To prevent damage to your pump and ensure satisfactory performance, you’ll need to verify that all fluid-handling components (body, manifolds, gaskets, O-rings, etc.) are made from materials compatible with the liquid you’re pumping. The WasteCorp chemical compatibility guide provides a quick reference for estimating the compatibility of various chemicals with common pump materials.
2. Type of fluid being handled.
The viscosity, temperature, and abrasiveness of the fluid you intend to pump also influence the type of pump you’ll need and its materials. For example, when transferring an abrasive liquid, wear-resistant materials such as steel (for the pump body) and NBR or Santoprene (for the membranes) are typically recommended. When transferring high-viscosity fluids, a pump with heavy metal components is required to provide adequate resistance, preventing performance loss. For a full breakdown of different pum materials and their ideal operating conditions, refer to our Comprehensive Guide to Diaphragm Pumps.
3. Operating environment.
It’s critical to consider the environment your pump will be operating in, including temperature, accessibility, and special requirements. For instance, do you plan to work on a remote site where a portable pump is required? Will there be explosion hazards present at the work site? Will you need to ensure your pump meets specific sanitary standards? Make sure you answer these questions before choosing a piston or diaphragm pump.
4. Your budget.
In addition to the upfront cost of the pump, you’ll need to budget for routine maintenance, energy consumption, and replacement parts.
Because so many complex factors influence the type of pump required for a specific task (and the materials of its components), we recommend contacting the experts at WasteCorp for assistance if you’re unsure what type of pump you need. Not only will we be happy to answer any questions you have, but we can also customize your pump to meet the demands of your application.
Performance Comparison of Diaphragm Pumps & Piston Pumps
Building on the information above, you can refine your pump selection by comparing
the specific attributes of piston pumps and diaphragm pumps, using the detailed guide below:
Power and Efficiency
Diaphragm Pump:
Because diaphragms utilize flexible materials, they increase resistance during pumping. This resistance results in a slight loss of performance and makes diaphragm pumps less energy-efficient than piston pumps. When using a diaphragm pump, you may also notice variations in flow rate due to the pulsating nature of the pump. As such, diaphragm pumps are most suitable for applications requiring low to moderate pressure and flow rates (e.g.,spraying weeds in close proximity).
Piston Pump:
Piston pumps transfer liquid using rigid components; as a result, they do not experience any performance loss during operation. Piston pumps are capable of handling high pressures and delivering precise, consistent flow rates. For this reason, piston pumps are often employed in field spraying and paint spraying applications.
Maintenance and Reliability
Diaphragm Pumps:
Diaphragm pumps offer unmatched durability and longevity, with many high-quality diaphragm pumps having a service life of several decades. Unlike piston pumps, they do not require frequent lubrication or inspection, and they’re forgiving of errors during use. To maintain a diaphragm pump, you will need to replace the diaphragms once per season (or after 300 hours of operation), but replacement of the diaphragms are typically very affordable.
Piston Pumps:
Piston pumps are more susceptible to wear and damage than diaphragm pumps due to the rigidity of their components. To keep a piston pump performing optimally, users must regularly lubricate the unit and follow proper operation protocols. Making a mistake while using a piston pump can result in costly damage. Even if you handle your piston pump with care, you will have to perform periodic inspections to check for signs of wear.
Fluid Compatibility and Flexibility
Diaphragm Pumps:
Diaphragm pumps are suitable for a wide range of fluids, including corrosive, abrasive, and highly viscous liquids, provided you select the correct diaphragm material for the substance you’re handling. Diaphragm pumps also offer excellent compatibility with chemically aggressive fluids. If your application requires the use of wettable powders or bleach solutions, for example, a diaphragm pump is the best choice.
Piston Pumps:
While piston pumps can pump viscous fluids at high pressures, they have limited fluid compatibility compared to diaphragm pumps. Due to their rigid materials and design, piston pumps can become damaged or clogged when exposed to corrosive or abrasive liquids. As such, they are most suitable for handling clean liquids that do not contain solid or abrasive particles.
Top Industry Applications
In addition to being a popular choice for agricultural spraying, piston pumps and diaphragm pumps play a key role in many different industries:
Diaphragm Pumps:
-Chemical processing, particularly the transfer of hazardous or flammable liquids.
– Pharmaceutical and food industries. Diaphragm pumps are frequently employed to pump dairy products, fruit slurries, creams, disinfectant solutions, and other shear-sensitive liquids.
-Waste management and sewage treatment, including septic tank pumping.
-Mining industry applications; e.g., the transfer of mineral slurry and dewatering.
Piston Pumps:
-Oil and gas industry processes, including fuel transfer, chemical injection, and drill cutting injection.
-Agricultural spraying (i.e., pesticides and herbicides) and irrigation systems.
-Automotive and manufacturing sectors; e.g., paint spraying, pressure-washing, and cleaning of manufacturing equipment.
Cost Considerations
The best way to keep costs low is to choose the correct pump type (and materials) for your application, preventing premature wear and tear. With that in mind, diaphragm pumps are generally more affordable than piston pumps over the long term. While diaphragm pumps may cost slightly more upfront, their low maintenance needs and long service life result in reduced operational costs. Piston pumps usually require more frequent and costly maintenance (including ongoing lubrication) due to the complexity of their design and the
nature of their operation.
Conclusion
Piston and diaphragm pumps offer similarly powerful, reliable performance when used correctly. To get the most value out of your pump, it’s crucial to make an informed purchasing decision that balances your objectives with your budget and the demands of your operating environment.
If you’re ready to choose a new pump, check out our diverse selection of diaphragm models or contact us for a custom pump quote today. Our experts will be happy to help you make the ideal choice for your pump for your needs.
Explore the full range of Diaphragm Pumps available at Wastecorp here: