What is the life (in cycles) for a hydraulic cylinder

[morfzcspls]

Does anyone know how many cycles (extend / retract) that a hydraulic cylinder should be able to do before needing repair?

The specifics for the cylinder are that there is minimal (almost none) low frequency and low amplitude pulsing of pressure. The cylinder will cycle once every 5 minutes for 20 hours each day, and pressure hold time will be 2 minutes each cycle. The weight against the cylinder produces very little side loading due to the weight riding on linear sleeve bearings. The environment is humid with temperatures ranging from 40° F to 90° F and it is approximately as clean as a typical basement utility room.

Cylinder bore: 5 inches.
Cylinder stroke: 60 inches
Cylinder press: 2200 PSI
Oil temperature: Will not exceed 100° F
Seals etc.: Assume high quality

I have searched many pages and spent many hours trying to get any kind of estimate or range, or guess. So if anyone has any knowledge of this, please respond.

 

[Mech_Engineer]

There's no way to know, it's specific to the cylinder and it's manufacturing tolerances. "Assume high quality" is not enough to venture a guess.

 

[Averagesupernova]

Usually will depend on the quality and contamination of oil. Environment will have some effect.

 

[morfzcspls]

Thanks for the response Mech_Engineer,

I need the number of cycles for a cylinder of high quality that is still considered to be of standard design. So I guess that means it would be a welded cylinder with chrome surfacing and the highest quality seals that do not require special design changes to use them. Also no other exotic features like bearings etc. I am really only looking for a reasonable estimate of the range, say plus or minus 25%. If you have experience with cylinder life situations perhaps you could give me an example, if not, it would be great if you could tell me how to calculate cycle life.

Thanks again

 

[Q_Goest]

Have you posed this question to your cylinder supplier? They're in the best position to provide a realistic answer.

I am really only looking for a reasonable estimate of the range, say plus or minus 25%.

I wouldn't trust even the most expert opinion to +/- 25%. If you can get within a factor of 3 to 10, that would be great. The only hydraulic cylinder I have experience with that I also have solid life cycle information on indicates the life of the unit will be around 10 million cycles.

I'd also agree with Averagesupernova, one of the primary factors in getting good life is oil contamination. Also, ensuring the exposed end of the rod doesn't accumulate dirt or corrosion will have a very significant affect. Lastly, temperature could be a factor if the hydraulic system isn't designed well so that heat generated by the system can be rejected.

 

[morfzcspls]

Thanks Averagesupernova,

Thanks for the advice. The pressure, temperature and environment for the cylinders is almost ideal for extended oil life but it could be changed out as often as needed. But that you mention it I may need to take that into account for operating cost.

Thanks

 

[morfzcspls]

Thanks Q_Goest,

That is great information. I have great control over all of the factors you brought up. When I said the environment was about equal to a basement utility room I meant like your basement utility room and that being a worst-case scenario. I have over a million BTUs of cooling capacity to cool the hydraulic fluid and I could cool the chamber containing the cylinders as well. Also the oil at all stages is in a building that has little or no dirt or dust etc. So thanks again for the information.

 

[Bandit127]

I work with injection moulding machines. They typically run 200 bar (3,000 psi) pressures. Each machine has 6 cylinders doing different jobs and we have about 50 machines. So, 300 cylinders in all. We probably have to fix half a dozen leaks a year.

Some leak with worn seals. Some leak with worn or scored cyliders. Very rarely a piston will snap.

These machines do about 2.5 million load/unload or move in/out cycles per year and are between 5 and 15 years old. So the average will be on about 25 m cycles. Age doesn't seem to be a factor in the probability of a leak, but we are more likely to have to change a piston on an older machine.

The oil contains zinc for cylinder lubrication. We test it every 3 months for particulate and chemical contamination. Also for viscosity. If it fails for particulates, we filter it with a 3 µm filter. If it fails for anything else, we replace it with new and filter the new stuff into the machine with a 3 µm filter. We replace the filters in the machine when the manufacturer says they should be changed. Mostly for process consistency, we run the oil at 40°C ±5°.

I hope (in a roundabout way) that I have helped to answer your question.

EDIT - the machines make medical devices so are in a clean environment.

 

[morfzcspls]

Thanks Bandit127,

The information you gave is the most comprehensive and useful I have received. Except for the pressure my use of cylinders will be very similar. The attention you pay to contamination is also very useful since, in my case, the cylinders will not be easy to access for repair.

Thanks again

 

[Enthalpy]

Even after having optimized every aspect for long life, I would NOT put hydraulic parts where they're difficult to access. Hydraulics does need regular maintenance, if only for inspection.

The scraper to protect seals from outside dirt must be quite important for long life. And seal wear is the very reason to put chromium on pistons, to my knowledge. Chromium gets ground in the length direction for that use, even at cylinders' inner face.

 

[morfzcspls]

Thank you Enthalpy,

I was planning to use chromium plating and I know too that the seals are critical but I consider these to be within the realm of high quality but not special designs. As for the regular inspection I will be able to do visual inspections but access to the cylinders is still going to be a problem. I am assuming just one million cycles between major overhauls in my system cost calculations. I am also using low pressures and I can live with minor leaks, that don’t greatly affect performance, since they cylinders are totally isolated from human activity.

Thanks,