You can find answers to many of your questions here.  Of course, we are always available to answer your questions by email or phone.

ASL’s patented Electrostatic System can filter a wide range of non-flammable, non-conductive and semi-conductive fluids and lubricants, including Hydraulic, Transformer, Turbine, Spindle, Lubricating, Transmission, Gear, Insulating, Compressor, cleaning solvents and synthetic oils and lubricants. Temperature of the fluid being filtered must be 155°F or less, and maximum viscosity of 1800 SUS @ 100°F

The short answer is no. Electrostatics cannot remove anything that is in suspension in the fluid. The exception would be additives that are spent, and have “fallen out” due to overheating, etc. These will then be treated as particulate and removed.

Electrostatic Systems have, by their very nature, fairly slow flow rates. Ideally, the ASL system should “cycle” the reservoir contents at least once every 24 to 30 hours. Therefore, a 30 GPH system should be used on reservoirs of about 720 gallons or less. 40 GPH, about 1200 gallons or less, 80 GPH about 2400 gallons or less, and 200 GPH about 7000 gallons or less. 

It really depends on how bad the fluid is initially, as well as new contaminate ingress rates. In general, about 6 to 10 cycles will be required to reduce fluid that is ISO 18/15/10, to ISO 10/7/0.


Absolutely! Tars and varnishes are the by-products of oxidation and oil degradation. Electrostatics has the unique ability to remove not only the “hard” particles, but also the “soft” particles, such as oil degradation by-products. Left unchecked, it is these degradation by-products that will plate out on critical surfaces, like valves, spools, pipes, bearings, etc. causing varnish, sludge build-up, and stiction, the leading causes of premature equipment failure. The first few passes of the fluid through the Electrostatic Cell will remove the pre-cursors of oxidation by-products, ridding the fluid of future build-ups. As the system cycles the fluid over time, existing build-ups are flaked off and return to the sump, where they are sucked into the Electrostatic Cell and retained.


First of all, the 4 cents per hour figure does not include the cost of electricity to operate the unit. The 4 cents per hour is based on one Electrostatic Cell exchange and one water absorber element change per year. Four cents X 8,760 (operating 24/7 for one year) = $350.40. At current pricing, you can replace both the Electrostatic Cell and water absorber element for around that.


Yes. The Phosphate Ester units use different cell and hose components than their mineral oil counterparts, and have a “P” in the model number. An FPRS-S40-Cab unit for Phosphate Ester fluid would be model number FPRS-S40P-Cab. Many of these units are in service at Nuclear power plants across the country.


Yes, however, your results may vary due to test conditions, sampling precautions and procedures, and the individual testing Laboratory’s standards. At an ISO of 10/7/0 there are only between .064 and 1.30 particles per milliliter greater than 5 microns, so getting a “clean” sample into a “clean” bottle and then testing the fluid, all without ANY outside contamination is very difficult at these low particle counts. On average, our customers report ISO 13/10/6.


All ASL units are equipped with a special design ASL/Simpson Microamperes meter. On the “E” Series units, the Microamp reading must be manually observed and noted. When the Microamp meter indicates 500 Microamps, the Electrostatic Cell should be back-flushed with 10 PSI. Shop air. On the “S” Series units, an Amber lamp will illuminate when the Microamp meter reads approximately 500 microamps, indicating time to back-flush.


All ASL Systems have a pressure gauge on the water absorber canister. With warm (100°F to 120°F) fluid, pressure will be low, approximately 10 to 20 PSI. When the gauge indicates pressures in the 35 to 40 PSI range with warm fluid, the water absorber element is most likely saturated, and should be replaced. Note that the ASL system pump is adjusted to be in “by-pass” at approximately 40 PSI.


The life limit of the Electrostatic Cell is 8,760 operating hours. (One year of 24/7 operations) Operation of the Cell beyond that, even though it may appear to be functioning properly, is definitely not recommended for four reasons:

  1. The electrical connections between the High Voltage DC power supply and the positive and negative plates can deteriorate, causing loss of power transfer.
  2. The electrical connections become coated with varnish, also rendering a loss of power transfer.
  3. At typical ingression rates, repeated back flushing in the 8700 operating hour range has little effect on improving the Cell’s ability to trap and hold particulate electrostatically.
  4. Shortened High Voltage Power Supply life. The number one reason for power supply replacement is operating a Cell beyond 8,760 hours.
  5. See the Question below: Why is the Microammeter your best tool?

The Microammeter is connected between the Electrostatic Cell’s Negative terminal and ground, and indicates how much power is being consumed by the Cell from the High Voltage Power Supply. The microammeter on your FPRS system should be checked frequently. When the system is new, and the oil in your reservoir is clean, microamp readings will be low. Normally, the meter will climb very slowly over time, and may take months to reach 500. On other systems, the meter could start at 200 and slowly climb, or even go down over time. The main thing to watch for is erratic movements, rapid climbing, etc. A rapid climb most always indicates water has entered the system, and finding and correcting the source of the water intrusion should be paramount. Once water has entered the Electrostatic Cell, concentrations of 600 ppm and higher, will short it out rapidly. Replacement of the water absorber and Backflushing the Electrostatic Cell (perhaps several times) will restore proper operation.

Changes in microammeter readings will also occur under the following fluid conditions:

  1. HEAT – Current Increases. Fluid temp. will cause the uA to increase. A rise from 80°F to 110°F can sometimes double the uA. In turn, as fluid temp. decreases, so will the uA.
  2. COOLING – Current decreases.
  3. WATER – Current increases. Water can make the “base current” appear higher than it really is.
  4. VARNISH – Current decreases. Although the Electrostatic Cell is capable of capturing a lot of varnish before it will effect the operation of the Cell, at some point, as the oil oxidizes, varnish will cause the efficiency of the cell to decrease, and the Cell will need to be replaced.

Approximately one and one-half pounds before back flush. One of the unique traits of Electrostatic Systems is their ability to trap and hold both “hard” particulate, and “soft” particulate such as oil degradation by-products that plate out on your system’s piping, valves, bearings, etc. causing varnish and sludge build-up. This is one of the main strengths of Electrostatic Fluid Filtration Systems, and is something that no other fluid filtration system can accomplish.


All ASL systems use a specially designed Stacked Disk Element with follower plate, specifically designed for the lower flow rates of Electrostatic kidney loop filtration. These elements are made of alternate stacked cotton and wood fiber discs, and are constructed to eliminate bypassing and channeling, assuring maximum filtration efficiency. The “E” and “S” Series unit’s water absorber element is designed to absorb 2 quarts of free and emulsified water, while the larger 80-SBO units element can hold up to 7 quarts of water. ASL Technologies Electrostatic Systems are the only systems of this type to incorporate water absorption as part of the system.


No. Electrostatics use High Voltage DC current to charge, polarize, and entrap particulate, so low fluid conductivity is critical for proper operation of the Electrostatic System. The system is designed for non-conductive, or semi-conductive fluids, lubricants and oils, both mineral and synthetic, such as hydraulic fluid, turbine oil, and the like.

While high procurement costs may exist from some of our competitors, ASL Electrostatic Fluid Purification Systems are the most cost effective systems on the market today. ASL system prices rival conventional off-line filtration systems, and, more often than not, can cost less than the fluid in your reservoir. Really!

ASL Electrostatic Systems use 15,000 VDC @1 milliamp. Research has shown that 15,000 volts is optimum for fluid filtration. However, with DC voltages in this area, the water content must be in the 300 to 500 ppm (KF) area to be effective without shorting out. This is one of the reasons that ASL incorporates a water absorber pre-filter to remove free and emulsified water from your fluid prior to the Electrostatic Cell. Other Electrostatic system manufacturers use much lower DC voltage in their Electrostatic chambers to tolerate this conductivity, but performance and efficiency suffer as a result.


The Unique design of the ASL Electrostatic Cell is such that it can be easily manufactured in a variety of positive to negative “spacing” to accommodate many different fluid conductivity levels. Hydraulic Fluid such as DTE-25, for example, has almost no conductivity, so Electrostatic Cells employed on this fluid have close positive to negative spacing. Fluid such as Air Conditioning compressor oil has higher conductivity, so the Electrostatic Cell for these applications is manufactured with somewhat wider positive to negative spacing. Phosphate Ester “fireproof” hydraulic fluids, which become more conductive as fluid temperature rises, require an Electrostatic Cell with even wider spacing. Note that there is no extra charge for any Electrostatic Cell configuration.

Quite frankly, there are several reasons.

  1. Initial Cost. ASL Systems are the lowest initial cost Electrostatic system on the market today, period. In fact our Electrostatic Systems are priced lower than many other conventional “size exclusion media” type systems.
  2. Performance. ASL systems have competed head-to-head against many other off-line filtration systems over the past 10 years, and we’ve always come out on top.
  3. Cost of operation. No other Electrostatic System can even come close to a 4 CENT per hour operating cost.
  4. Ease of maintenance. ASL Electrostatic systems are the most maintenance-friendly systems out there. Quick disconnects on the Electrostatic Cell, makes for a 5 minute, hands clean operation.
  5. Back flush ability. No other Electrostatic system can be back-flushed with shop air to extend Cell life to an unprecedented one-year interval.
  6. Longevity. ASL Electrostatic Systems have accumulated over 20 million operating hours. We’ve been around.
  7. Personalized service. When you call ASL, you’ll speak to a real person, someone who knows the system, and can get you the answers you need, not some answering machine with multiple menus to traverse. You’ll get the same people too, not a “new face” every time you call.

As stated previously, the life span of an Electrostatic Cell is approximately one year of 24/7 operation, or 8760 operating hours. At this point, the Electrostatic Cell should be replaced with a new one. ASL re-manufactures thousands of Electrostatic Cells each year, so fresh cells are always on the shelf. In order to keep costs as low as possible, ASL needs your spent Electrostatic Cell core returned. Each returned core is completely disassembled, cleaned and inspected. The internal components are disposed of, and only the tube and end caps are re-used, provided they meet stringent requirements. All internal components are replaced with new parts; the Cell is tested, labeled and packaged. As your Electrostatic Cell nears the 8760-hour point, a fresh cell can be shipped to you in advance. After installing the new Cell, place the used cell in the shipping container the new cell arrived in, and return it to ASL. We will allow 30 days to receive your spent Cell, before reminding you. Spent Cells that are not returned are subject to a core charge.


If you can’t find the answer to your question, contact us!