What You Need to Know About Your Hydraulic Pump Lifespan ?
Do you know how long any hydraulic pump should last? In this industry, using past experience might not always deliver the answers you were hoping for, and are likely to give you answers that are actually no better than guessing.
Disappointingly, there is no dependable approach to determine how long your hydraulic pump will last. Using historical data is perhaps something that will give you the best indicator, but if it’s a new pump and you have no data – that’s where the guessing game beings. Fortunately, there are a number of factors that determine how long any pump will last and using these can give you an estimate that is more informed.
For example, let’s consider your hydraulic system. The type of application it is will make a different to the pump life and so will the temperature. Using pumps that are graded as ‘industrial grade’ will deliver a better lifespan than those that are not. Using auxiliary information can also help. For example, an axial piston design pump has less heavily loaded shaft bearings and therefore are not at a great risk of premature failure.
Of course, roller type bearings in this type of piston design can fail prematurely due to brinelling. That’s why it’s better to use shell-type bearings as they are more like a bushing than a bearing.
Another major consideration is the type and grade of oil being used. If it’s ‘special purpose’ and is fire resistant then it won’t always have a positive influence on the service life. However, it will run cool which could help with its lifespan as there will be less temperature related lubrication issues.
Keeping a high level of oil cleanliness will also work well in extending the life of anyhydraulic component.
Another point to ponder is how hard the pump is working. This is about how fast it’s spinning and under what pressure –how much of each hour is the pump under load? If they are under load for 55 minutes of every hour, then that’s going to be a 90% duty cycle, which is a lot to maintain compared to being under load for say 42 minutes of every hour. Under ideal conditions such as a duty cycle of 70% or less, 1200 rpm spinning with clean oil, you can hope an industrial grade hydraulic pump would last 20,000 hours or more. However, if you’ve got a 90% load with special purpose oil and 1800 rpm then you are more likely to get something in the arena of 10,000 hours of service life.
Running To Failure
There’s no doubt that these are only informed estimates using the information that we have about the pump and how it’s being used. Of course, if there are any hidden design flaws then the lifespan of the pump could be drastically compromised. For example, if there are pressure spikes that are caused by rapid valve shifts, then over time this could lead to a pump failure.
To continue to run a hydraulic pump until it fails is not a good idea. Its failure could cause consequential damage to other components. The cost of the rebuild of the pump will increase. Changing a pump before its life expires should be managed, whilst historical data is collected.
So if it’s looking like 20,000 hours is a strong lifespan possibility for any pump, then it’s wise to pull it out at 12,000 hours. It can be inspected and put back into service until say 15,000 hours. Then run to 17,500 hours and if all is well, then run until 20,000 hours. Getting too greedy will put the pump into the correct timeframe for a failure, so it’s not wise to push it too far.
Using this approach can provide information to make informed decisions on realistic expectations for component lifespan without putting the hydraulic system at great risk.
This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.
The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.
In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.
Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.
Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.
Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.
Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.
In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.
Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite.
It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1.
It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.
In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.