Pumping system operators seeking durable, low-maintenance, easy-to-run equipment for fluid management often look to air-operated diaphragm (AOD) pumps. These pumps can move fluids of low or high viscosity, and are ideal for use with wastewater, abrasives, caustic materials or slurries. They are also rugged, can tolerate aggressive conditions and, if maintained properly, last for many years. However, a clean, dry air supply can increase their performance and durability benefits. Particulates often creep into the pumping air supply through moist, oily, or dirty environments, corroded pipes with scale, or due to extreme temperatures. For example, pumping equipment may need to operate on a dusty oil rig, a low-temperature food processing plant, or in an industrial setting contaminated with dirt, oil or sludge. Selecting the right pump and accessories for the application as well as conducting regular maintenance will help mitigate the obstacles of dirty, moist and oily air for top pump performance, cost efficiency and reliable operation.
Performance reduction
Modern air-operated diaphragm pumps are self-priming, running without added lubrication. Excessive oil or moisture in the intake air supply can negatively affect the original assembly lubrication in the pump's motor portion and reduce its performance. Problems occur when contaminated air passes through openings causing degradation to components in the pump's air motor. Dirt particles and grit can wear out valve mechanisms causing abrasion and premature equipment failure while dirt or sludge build up degrades seals and bearings. Moisture in the air supply can also wreak as much havoc as dirt, and can significantly damage motor components costing 10% or more of the original pump price to repair or replace. Too much moisture can result in ice buildup and freezing of exhaust air due to an accumulation of ice particles that clog the motor area and muffler, causing the pump to slow or even seize.Overall, lack of clean air supply adds costs to the pumping operation, due to worn components, failure risks, lower performance and reduced energy efficiency.
Choose the right pump
Avoiding problems from contaminated air supply includes both preventing air contamination and choosing a reliable, durable pump that fits the application and the operating environment. An expert from a pump supplier or manufacturer can help the operator analyze the needs, considering fluid type and composition, flow rate, pressure, viscosity, temperature and ambient conditions in the decision. Identifying the proper size, capacity, pump construction and accessories for the demands of the operating conditions reduces problems associated with a poor or unconditioned air supply. ARO® pumps, for example, are designed to minimize the effects that dirty air can have on major valve assemblies. These pumps also include features to eliminate pump ice-up by diverting cold, wet exhaust air away from the major air valve eliminating pump stalling due to ice build-up. This technology makes external ice-prevention devices unnecessary. There are things to look for in an air-operated pump that maximize the reliability and longevity of the pump while also helping minimize problems associated with a contaminated air supply. The patented air-motor technology in ARO EXP Series pumps features a unique air valve design. The D valves are constructed with ultra hard ceramic that is impervious to dirt and grit in the air. It also includes Quick Dump™ Checks to eliminate pump ice-up, as well as a corrosion-resistant and a durable thermoplastic exterior. EXP pumps also use u-cups that are less likely to fail due to poor air compared to glide rings or lap fits in some pumps.
Filters and regulators
Pump operators should use filters and regulators when needed to condition the air supply. This encourages more reliable pump performance and reduces equipment wear and related energy costs. Air intake filters for the pumping system are designed to remove contaminants from compressed air, preventing damage and reducing production losses due to contaminant-related downtime. There are three primary types of filters—general purpose to remove water and reduce abrasive contamination; coalescing to remove oil aerosols and particles down to 0.3 micron and vapor. General purpose and oil removal filters are selected by flow capacity. Operators should size filters based on OEM-recommended flow ratings and always install filters in the airline upstream of regulators, lubricators, control valves and air-operated equipment. In most cases, higher-quality air filters provide a lower pressure drop, increase overall efficiency and extend service time. When comparing filters, operators should consider both pressure drop at in-use and maximum flow levels. Over time, all filter elements reach their contaminate-holding capacity due to dirt, scale and rust, causing the pressure differential across the filter to rise. General-purpose elements should be changed when the pressure drop is less than seven psi, while higher-efficiency elements can be replaced at 10 psi. If the filter is outfitted with a pressure-drop indicator, it will automatically signal when a filter replacement is needed.
'PIggybacks'
Filter-regulators, or 'piggybacks', combine the functions of both a filter and regulator. Piggybacks are compact and often fit the bill when space is constrained. Filter regulator lubricators (FRLs) take air from a compressor, which can be hot, wet and dirty, and make it safer for use in the pumping system. FRLs come with different filter elements and can be modified with various springs, depending on the filtration and air regulating requirements. Factory assembled and tested, these units save both time and the cost of building an integrated system from individual components. When selecting an FRL, operators should look for one with standard safety features such as locking bowls, lockout, check and soft-start valves to safely control and manage the air supply. The FRL will direct the excess moisture from the air stream to the bottom of the filter bowl. The filter housing should be drained daily to release any condensate. Choosing one with an automatic drain option simplifies this process, saving time and protecting the system from water re-entrainment.
Additional lubrication
In select circumstances additional lubrication may be necessary including applications with a high cycle rate, extremely poor air quality conditions or when nitrogen is being used to run an air operated pump. This requires an air-line lubricator that adds controlled quantities of non-detergent oil into the system to deliver a constant ratio of oil to air flow. Pump manufacturers provide charts to help users determine lubricator pressure drop at the required flow rate and pressure. If you have need of a lubricator, install it as close as possible to the pump and after any filter-regulator assembly. A quality grade of 80-90 weight non-detergent oil or straight 90 weight non-detergent oil not to exceed one drop per minute is recommended.
Conclusions
With air-operated diaphragm pumping systems, good air quality is critical to reliable and efficient pump performance. Maintaining clean air requires selecting a pump capable of handling a wide variety of air intake qualities, installing the right accessories and regular maintenance. A fluid management expert can help identify the necessary steps to keep down costs and minimize downtime related to air quality issues.
Notes
Oil grade recommendations are specific to ARO/Ingersoll Rand pumps and may or may not apply to other brands.
