The cleanliness code your pump needs depends on the pump type and the pressure it runs at: Vickers sets 17/15/13 for a variable piston pump working at 2,000-3,000 psi and 16/14/12 above 3,000 psi, while Rexroth sets 20/18/15 as the minimum for its A10VSO and A4VG piston pumps. After a pump failure, drain the oil, clean out the reservoir, flush every line and component, fit new filters, then change those filters again after the first 40 to 50 hours, or the metal from the old pump will take out the new one.
Vickers put it bluntly in its contamination guide: when hydraulic problems turn up, 80% of the time they trace back to poor contamination control. Below are the factory numbers, brand by brand, and the flushing routine we want done before a rebuilt pump goes back in.
Read the code, not the brochure: a cleanliness target only means something next to a lab particle count. If nobody has ever sampled the oil, you do not know your code, and every filter decision after that is a guess.
What does an ISO 4406 code like 18/16/13 mean?
An ISO 4406 code is three numbers, each one a scale step for how many particles are in one milliliter of oil. Under the current standard (ISO 4406:1999) the first number counts particles larger than 4 micrometers, the second larger than 6, and the third larger than 14. Danfoss and Rexroth both spell out the key rule: each step up the scale doubles the particle count, and each step down halves it. So 19/17/14 is roughly twice as dirty as 18/16/13 at every size.
| Scale number | Particles per milliliter |
|---|---|
| 21 | 10,000 to 20,000 |
| 20 | 5,000 to 10,000 |
| 19 | 2,500 to 5,000 |
| 18 | 1,300 to 2,500 |
| 17 | 640 to 1,300 |
| 16 | 320 to 640 |
| 15 | 160 to 320 |
| 14 | 80 to 160 |
| 13 | 40 to 80 |
| 12 | 20 to 40 |
Decoded, 18/16/13 means 1,300 to 2,500 particles per milliliter above 4 micrometers, 320 to 640 above 6, and 40 to 80 above 14. Older reports use two numbers (for example 18/13), which count only the 5 and 15 micrometer sizes from the 1987 version of the standard. Danfoss notes that the 1987 and 1999 counting methods land on the same class for the same sample.
Why chase particles that small? Vickers puts the manufacturing clearances in high pressure components at up to 5 micrometers, and up to 20 micrometers in lower pressure parts. The particles that do the damage are the ones that just bridge those gaps.
Watch the first number when you compare brands. The Vickers 561 chart counts its first number at 2 micrometers, not 4. The second and third numbers line up across brands; the first does not. Compare like with like, and ask your lab which method it used.
What ISO cleanliness code does my hydraulic pump need?
Set the target by the most sensitive component on the reservoir, at the highest pressure the machine reaches in its cycle. This is the Vickers recommended chart from Eaton document 561. It is a long-life target, not a minimum.
| Component (Vickers 561) | Under 2,000 psi (140 bar) | 2,000-3,000 psi (140-210 bar) | Over 3,000 psi (210 bar) |
|---|---|---|---|
| Fixed gear pump | 20/18/15 | 19/17/15 | 18/16/13 |
| Fixed vane pump | 20/18/15 | 19/17/14 | 18/16/13 |
| Fixed piston pump | 19/17/15 | 18/16/14 | 17/15/13 |
| Variable vane pump | 19/17/15 | 18/16/14 | 17/15/13 |
| Variable piston pump | 18/16/14 | 17/15/13 | 16/14/12 |
| Gear motor | 21/19/17 | 20/18/15 | 19/17/14 |
| Vane motor | 20/18/15 | 19/17/14 | 18/16/13 |
| Axial piston motor | 19/17/14 | 18/16/13 | 17/15/12 |
| Swashplate design motor | 18/16/14 | 17/15/13 | 16/14/12 |
| Hydrostatic transmission (in-loop fluid) | 17/15/13 | 16/14/12* | 16/14/11* |
| Proportional directional valve | 18/16/13 (up to 3,000 psi) | 17/15/12* | |
| Servo valve | 16/14/11* (up to 3,000 psi) | 15/13/10* | |
* Vickers flags these as needing precise sampling practice to verify.
Other factories publish their own numbers, and most are written as the minimum the unit must see, which is why they read dirtier than the Vickers chart:
| Brand and document | Unit | Published code |
|---|---|---|
| Rexroth RE 92711 (A10VSO Series 31) | Open circuit piston pump | At least 20/18/15; at least 19/17/14 when the fluid runs very hot (up to 110 °C at the drain port) |
| Rexroth RE 92003 (A4VG Series 32) | Closed circuit piston pump | At least 20/18/15; at least 19/17/14 from 90 to 115 °C |
| Rexroth RE 90220 | General, and servo valves | 20/18/15 or better; servo valves at least 18/16/13 |
| Danfoss 520L0467 | Axial and radial piston pumps and motors, gear pumps and motors | 22/18/13 |
| Danfoss 520L0467 | Orbital motors | 22/20/16 |
| Danfoss 520L0467 | Cartridge and electrohydraulic valves | 18/16/13 |
| Eaton 03-401 (2010) | Vickers PVM, PVH, PVE, PVQ, PVB piston pumps | 21/18/13 |
| Eaton 03-401 (2010) | Vickers vane pumps, industrial and mobile | 18/16/13 |
| Eaton 03-401 (2010) | Char-Lynn J, R, T, S, disc valve and VIS motors | 20/18/13 |
| Eaton 03-401 (2010) | Heavy-duty piston pumps and motors | 21/18/13 |
| Parker HY29-0035 (Denison T6, T7, T67) | Vane pumps | 19/17/14 or better |
| Parker HY28-2662 | PVP piston pumps | Maintain 16/13, 18/15 maximum (two-number code) |
Our take: the published minimum is the floor. The Vickers chart is what keeps the pump alive. If the machine matters, run to the cleaner number.
When to set the target cleaner
- Fluid that is not straight petroleum oil: one range code cleaner at every size (Vickers 561). Water glycol at a 17/15/13 target becomes 16/14/12.
- Two or more of these conditions: frequent cold starts below 0 °F (-18 °C), intermittent running above 160 °F (70 °C), high vibration or shock, or a machine the whole process depends on. Go one more code cleaner (Vickers 561).
- Test stands: one code cleaner than the most sensitive unit being tested (Vickers 1992 target worksheet).
New oil is not clean oil
Vickers found new oil from reputable suppliers typically arrives at 17/16/14 or dirtier on its three-number scale. Rexroth says plainly that delivered oil usually does not meet its component requirements. Danfoss sets 23/21/15 as the minimum for a fluid change or top-up. Pump new oil in through a filter cart, every time. Pouring from an open bucket undoes everything else on this page.
What do filter beta ratios mean?
A beta ratio is the particle count upstream of a filter divided by the count downstream, at a stated particle size, from the multipass test. A filter rated beta 10 = 75 lets 1 particle larger than 10 micrometers through for every 75 that arrive.
| Beta ratio | Capture efficiency |
|---|---|
| 2 | 50% |
| 10 | 90% |
| 20 | 95% |
| 75 | 98.7% |
| 100 | 99% |
| 200 | 99.5% |
| 1000 | 99.9% |
Danfoss notes that going from beta 50 to 75 buys only about 0.67% more efficiency, so a sky-high beta on the box is mostly marketing. Vickers adds that lab beta numbers correlate poorly with real system cleanliness, because flow swings, pressure pulses and cold starts stress the element. Well-supported pleats and a downstream wire mesh hold up; floppy pleats do not.
Factory guidance on ratings: Vickers says to select filters at beta 100 or better for the size you care about. Rexroth recommends beta 20 of 100 or more for the A4VG. Danfoss recommends beta 15-20 = 75 on charge pressure filters in closed circuits, and beta 35-45 = 75 on suction filters, with a 100-125 micrometer suction screen in front of any charge or return line filter setup.
Where should the filters go?
- Pressure line: directly after any fixed pump running above 2,250 psi (155 bar) or variable pump above 1,500 psi (103 bar), and always when the system has servo or proportional valves (Vickers 561).
- Return line: a good main filter location as long as it sees at least 20% of system volume per minute. If the pump sits in compensation and return flow drops below that, add a recirculating (kidney loop) pump and filter (Vickers 561).
- Breather: every reservoir vent needs filtering to 3 micrometers (Vickers 561). Dirt is far easier to stop in the air than to pull out of the oil.
- Closed loop: a high efficiency filter on the charge circuit is the normal setup. For hydrostatic drives running near maximum pressure, Vickers recommends in-loop filters, which also protect the motor if the pump fails.
- Ahead of servo and proportional valves: a non-bypass isolation filter, never finer than the system filter, or it ends up doing the whole system's clean-up and plugs fast (Vickers 561).
- Not in the case drain. Vickers specifically warns against it: back pressure in the case wears out the shaft seal. See hydraulic pump leaking from the shaft.
- Suction: Parker does not recommend suction filters on the PVP or inlet strainers on Denison T6 and T7 vane pumps. Starving the inlet costs more than it saves.
Fit an indicator on every filter and change the element when it trips. An element on bypass is not a filter.
How and when should I sample the oil?
Take the sample from the return line just ahead of the return filter, with the system running or just shut down so the dirt is still in suspension; Vickers recommends a permanent sampling valve there. A reservoir sample is the least reliable; if you must, put the tube about halfway down. Danfoss specifies sampling in the loop or at the pump inlet for its units.
| Vickers sampling interval | Under 2,000 psi | 2,000-3,000 psi | Over 3,000 psi |
|---|---|---|---|
| Target 17/15/12 or cleaner, 8 hours a day | 4 months | 3 months | 3 months |
| Target 17/15/12 or cleaner, over 8 hours a day | 3 months | 2 months | 2 months |
| Target 18/16/13 or dirtier, 8 hours a day | 6 months | 4 months | 4 months |
| Target 18/16/13 or dirtier, over 8 hours a day | 4 months | 3 months | 2 months |
After commissioning or a major rebuild, Vickers calls for a sample on the first day and after one month, plus one before start-up and one after a week on large systems (530 gallons and up) or anything with servo valves. Sample again after any maintenance event such as a hose change or pump repair, and immediately if the system starts running hot, erratic or noisy.
What the lab report should cover, per Rexroth RE 90220: viscosity at 40 °C and 100 °C, acid number, water content by Karl Fischer, an ISO 4406 particle count, and wear and additive elements, compared against the new oil. Danfoss adds two useful flags: a sudden rise in wear metals means a failure is coming or has started, and silicon (dust) above 10-15 mg/kg calls for an oil change.
Why does a pump failure contaminate the whole system?
A pump that comes apart sends its own metal downstream, and Vickers notes that system-generated particles are work hardened, harder than the surfaces they came from, and very aggressive at causing further wear. Left in circulation, they generate more particles at an accelerating rate. That debris lands in valves, cylinders, the cooler, the hoses and the reservoir floor.
Closed loop hydrostatic drives are worse. Danfoss explains why: without loop flushing, the only way dirt leaves a closed circuit is through internal leakage, so only particles smaller than the leak gaps get out. Everything bigger stays in the loop, which means the motor and the loop lines are holding the remains of the pump.
How do I flush a hydraulic system after a pump failure?
This is the routine Vickers lays out in its Hydraulic Hints guide (694) for a failed pump or motor, with the flushing and start-up detail from Vickers 561 and the Danfoss Series 90 service manual folded in.
- Look before you drain. Check the oil and the filter for discoloration, foam, sludge and metal (Danfoss Series 90 manual). Cut the filter open. What you find tells you what failed, and whether something other than the pump caused it.
- Drain it warm. Run the system to heat the oil before draining so it flows and carries suspended dirt out with it. Drain at the lowest point and get all of it (Vickers 694). Do not reuse the oil.
- Clean the reservoir. Drain, flush and clean it out, and remove all residual sludge and debris (Vickers 694 and the Vickers catalog contaminant control page). Use lint-free rags, not shop towels.
- Flush and inspect the rest of the circuit. Inspect hoses, lines, cylinders and valves for wear and pieces of the failed unit, and flush every component to remove metal (Vickers 694). Flushing works on velocity and turbulence: low viscosity fluid or system oil at elevated temperature, with every valve cycled so flow reaches every line (Vickers 561). Bridge out cylinders and servo valves with jumpers while flushing (Vickers catalog contaminant control page).
- Deal with the motor in a closed loop. It sat downstream of the failure in a circuit that cannot purge large particles. Our advice is to tear it down and clean it, or rebuild it, along with the pump. Bolting a new pump to a contaminated motor is how you buy two pumps.
- Fit new filter elements everywhere (Vickers 694).
- Refill through a filter and fill the pump case with clean oil before start-up. Danfoss specifies a 10 micron filler filter on Series 90 systems; the older Vickers 694 guide says 25 micron.
- Run it in off-load. Vickers calls an off-load running-in period essential for any rebuilt system. On a hydrostatic drive, Danfoss says to cycle forward and reverse for at least five minutes to bleed air and flush the loop, and says not to run at maximum pressure until the oil is air-free and filtered.
- Change the filters again after 40 to 50 hours (Vickers 694). Rexroth warns that heavy start-up contamination can mean a fluid or filter change within the first 50 operating hours.
- Sample to prove it. Vickers sets the flushing target two ISO codes below the operating target, so flush cleaner than you plan to run.
Skip the flush and the new pump eats the old one. Vickers lists "failure to purge debris from the system after a pump failure" as a maintenance cause of contamination in its own guide. That is how a fresh rebuild ends up back on the bench with the same scoring as the unit it replaced.
What happens to the warranty if the system was not cleaned?
Read the factory paperwork and the answer is consistent. Danfoss states that its component warranty does not apply to fluid-related damage unless it has been expressly granted. Its Series 90 service manual warns that contamination can damage internal components and void the warranty. Rexroth says it accepts no liability for damage caused by failing to follow its fluid requirements.
Whoever stands behind your pump, expect any warranty conversation to start with the oil. Keep the records: the flush, the filter changes with dates and hours, and the sample results. That paperwork protects you more than anything else on this page.
Frequently asked questions
What ISO cleanliness code does a hydraulic piston pump need?
Vickers recommends 18/16/14 for a variable piston pump under 2,000 psi, 17/15/13 at 2,000-3,000 psi and 16/14/12 above 3,000 psi. Rexroth sets 20/18/15 as the minimum for the A10VSO and A4VG, tightening to 19/17/14 when the fluid runs very hot. Danfoss lists 22/18/13 for its axial piston pumps and motors.
What does 18/16/13 mean?
It is an ISO 4406 code. Under the 1999 standard it means 1,300 to 2,500 particles per milliliter larger than 4 micrometers, 320 to 640 larger than 6 micrometers, and 40 to 80 larger than 14 micrometers. Each step in the scale doubles or halves the count.
How do I flush a hydraulic system after a pump failure?
Drain the oil warm, clean out the reservoir, inspect and flush every hose, line, valve and cylinder, clean or rebuild the motor on a closed loop drive, fit new filters, refill through a filter, run in off-load, and change the filters again after 40 to 50 hours. That follows the Vickers procedure from its Hydraulic Hints guide, plus the closed loop motor check from our own shop practice.
Do I need to replace the hydraulic oil after a pump failure?
Yes. Vickers calls for disposing of the fluid removed from the system and filling with clean fluid. Filtering the old oil does not get the metal out of the reservoir, lines and components it has already settled in.
What beta ratio filter should I use?
Vickers recommends beta 100 or better at the particle size you are controlling, and Rexroth recommends beta 20 of 100 or more for the A4VG. Danfoss uses beta 15-20 = 75 on closed circuit charge filters. The beta number alone does not set system cleanliness; filter location and flow matter as much.
About the technical information on this page. Figures, procedures and part numbers here come from manufacturer service literature and are provided for reference only. They are only as accurate as the factory data, and the revision we have on file may not be the latest for your unit. Always confirm against the current manufacturer documentation for your exact model and follow safe work practices. RestoPower is not responsible for damage, injury or loss resulting from the use or misuse of this information, or from incorrect assembly, adjustment, installation or operation of any unit.
Pump failed? Tell us about the pump and what the filter looked like
We rebuild the pump, and on a closed loop drive we will look at the motor too. Every repair starts with a free teardown evaluation and a firm itemized quote before any billable work. Work done in our shop carries a 1-year repair warranty.
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