Air pump technology plays a critical role in various wastewater and environmental applications. Using compressed air to aerate water is the most well-known, but the movement created by air has many uses in the wastewater industry. Utilizing positive and negative air pressure to move liquids in an indirect way is another popular application. This method is advantageous because the medium does not have to pass through the pump.
The range of applications in wastewater and general water processing is as broad as the range of pump types and technologies. How can users know what pump type is the best fit? Simplified, the two main factors to make the right pump choice are the needed differential pressure and volume flow.
For high flow but moderate differential pressure, radial, regenerative and lobe blowers are an excellent choice. Radial and regenerative blowers offer the added benefit of being maintenance free. Both are dry running, which means that no operating fluid is needed. Lobe blowers, also known as roots blowers, are dry running as well but carry oil in the gear box and are sometimes equipped with gaskets on the rotors that need maintenance. Lobe blowers have two benefits when compared to radial and regenerative blowers: they are available in larger frame sizes and can reach higher differential pressures. For applications where higher pressures are needed, rotary vane pumps, claw pumps and screw pumps are the dominant technologies. For smaller demands of air, diaphragm and piston pumps can also be found.
Rotary vane pumps are available as dry running or oil lubricated, but oil-lubricated rotary vane pumps are more dominant in the vacuum category. In a dry-running rotary pump, the compression chamber is lubricated by the abrasion of the carbon graphite vanes. Oil-lubricated pumps recirculate oil and use lubricant as coolant through the system. The oil is separated from the gas stream before leaving the pump. Both types of rotary vane pumps are popular because of their straightforward design and durability. The oil lubrication helps to make the pump more robust against moisture and assists the pump in achieving higher levels of vacuum.
The downside of oil-lubricated rotary vane pumps is the need for more maintenance in general. The pump oil and oil-separating filter elements must be replaced regularly. Dry rotary vane pumps have notably longer service intervals. The carbon graphite vanes must be replaced as soon as they have worn down to a critical height. Depending on the type of dry rotary vane pump, the service intervals can be four to 10 times longer than oil-lubricated rotary vane pumps.
In recent years, claw technology has gained popularity as a near maintenance-free alternative. Claw pumps are another type of dry-running pump. Claw pumps use rotating, claw-shaped rotors that grab air and pull it into the pump inlet to create suction. As the rotors rotate, the claws open to grab air, close to trap it in the rotors and transport it to the pump outlet where the air is discharged. The only operating fluid is in the gear box. Due to the two-shaft design and complexity of the pump, the initial investment and repair cost are higher compared to rotary vane pumps.
The last category of popular pumps are screw compressors. They are available in dry and oil-lubricated versions. Screw compressors contain two interlocking rotors that turn in opposite directions. As the rotors rotate, air enters the space between them and gets compressed into a smaller volume as the space between the rotors and housing decreases. Dry systems are higher in initial investment cost but lower in maintenance cost. The cost for oil and oil-separating filter elements can add up quickly.
Common Applications Using Pressure Pumps
Aeration is one of the most common applications users have questions about. Aeration is introducing air to a body of water and can be used in a variety of processes. From septic tanks or pools to amusement parks, a positive pressure pump can save money and time. Here are some different applications and the pump types that can be used.
In a septic tank, a positive pressure pump like a compressor (diaphragm, piston, rotary vane) or blower (radial or regenerative) can be used to improve bacterial and microorganism growth to expedite organic breakdown and reduce smell. In commercial sewage plants, the wastewater of whole communities and cities must be treated properly and efficiently. The air demand required for this is usually generated by big installations of lobe blowers. Single pump units are often used for specific tasks like the pre-separation of sand and gravel or fat and oils from the sewage. These materials are lighter or heavier than the rest of the wastewater, making them easy to separate with the help of compressed air. This separation is usually accomplished by using a rotary vane or claw compressor to create a blast air curtain for the sewage to pass through. The lighter materials separate from the sewage and collect at the top of the water, while the heavier particles sink to the ground.
Another form of aeration occurs in ponds, fish hatcheries, aquacultures and other bodies of water. The introduction of air helps local aquatic life by promoting healthy oxygen levels in the water and reducing stagnant water and algae growth. The constant movement of water also helps maintain consistent temperature and reduce ice buildup in the winter. Pump choice is usually driven by the length and diameter of piping, water depth and the type of aeration equipment being used. Typically, this type of aeration utilizes various blower technologies like radial, regenerative or positive displacement blowers. In deeper water, rotary vane or claw style compressors are preferred because deeper water requires higher air pressure.
Another application is sand filter backflushing, which is typically used by water parks and other large industrial applications where sand is used to clean water. Sand filters need to be backflushed regularly to remove all captured particles. Larger systems not only use water for this process, but also compressed air to lift and clean the sand. Low-pressure compressors like a piston or rotary vane compressor are more energy efficient than conventional air compressors, while still providing the desired pressure levels for this application.
Common Applications Using Vacuum Pumps
As referenced, the use of air is not limited to positive pressure applications. Negative pressure pumps, such as dry vane and oil-lubricated vacuum pumps, can be used in an assortment of wastewater industries.
For example, most dewatering pumps need to be primed for the best performance. Larger volume of transfer (distance and height difference to the water) typically requires a vacuum pump for more efficient usage.
Utilizing vacuum for the lowering or removing of groundwater in construction sites and other applications where standing water is present is another commonly seen application. Vacuum is used to pull the water to a large collection vessel when groundwater is present. This is a great and energy-efficient way to remove water over longer periods of time and with varying levels of water.
Vacuum sewers also utilize vacuum pumps like oil-lubricated or claw pumps. Vacuum-supported sewer systems are found in many areas where conventional sewer systems cannot be used or are not the best choice, typically in low-populated and flat areas. Vacuum-sewer pipes are usually made of polyvinyl chloride (PVC), have significantly smaller diameters and do not need gravity to operate like conventional concrete sewer systems. The PVC pipes and small diameters enable low-cost systems that can cover long distances and can be installed in soft soil.
Vacuum can also be used for highly populated and mobile applications where a lot of sewage must be transported quickly, such as on cruise ships where thousands of people live in close quarters. Pumps are located at pumping stations and generate the needed vacuum to pull the wastewater from the source to the separation tank.
With all these pump technologies and applications, it is important to be mindful of corrosion that can be a factor when pumps are exposed to moisture from the process and/or humidity. Humidity during the time the pumps are not in operation is also a risk for some applications where the pumps are only used during a season, like water parks. During the off-season, rust buildup can occur on the pumps.
Most pump manufacturers offer pumps with corrosion protection to help with this. Corrosion protection is often created by special surface treatment of components and moisture-resistant accessories. Additional information on how to prevent corrosion is often found in the pump operating instructions or from the pump or system manufacturer.
Due to the complexity of the pumps and vast range of applications and operating factors, talking to a specialist or a pump manufacturer is recommended when purchasing a new pump or replacing an existing pump. While multiple pumps will often work for the desired application, an experienced pump specialist will help select the right pump for the individual use case.