These days we expect hydraulic pumps should be fully supported with detailed technical information ensuring that we use the pump in the correct application.
Often we have pages of stuff showing everything from displacement to recommended oil type.
I often find that the pressure duty is not well defined like what pressure can I safely generate without the pump falling apart. You will read descriptions like continuous, intermittent and peak.
Continuous speaks for itself but what about intermittent and peak, what does this description really mean.
Many years ago when I sold hydraulic components for a well known manufacturer the pumps had different ratings for industrial than mobile. For what I can only imagine were commercial reasons, the mobile pump pressures were much higher.
I have also used some pumps well outside their recommended pressure ranges (only for specific applications) and although not a practice I recommend I do wonder what technical basis manufacturers use to determine their pump pressure ratings.
I would like to see a graph with a direct correlation between pressure and life. I want to know that if I design a system that runs once a month for 15minutes at higher than normal pressure should I need to spend much more money on a more expensive pump.
Surely we should be able to get a better idea of pump life without always having to buy the highest spec pump or face the possibility of a bucket of scrap metal after just a few cycles.
Very best
Bob
Showing posts with label hydraulic pump. Show all posts
Showing posts with label hydraulic pump. Show all posts
Saturday, 29 October 2011
Monday, 6 June 2011
Pump Design
I am sure pump designers would love to find ways to completely eliminate, Pressure drop across the pump (with free outlet) together with, friction, noise and heat. (wasted energy) but this is the price we pay to get the flow through the pump. These are the “undesirables” of pump design we must live with (due to physics) although with better design and technology we continue to improve.
Flow is the desirable product we want from the pump and it is important that we make the pump strong enough to resist any restriction of that flow up to a maximum design pressure. After that we will likely cause damage to the pump.
So how does the pressure change within the pump?
1) By increasing pump speed (increasing the flow)
2) Changing the oil (resisting flow)
3) Adding a load (resisting flow)
4) Pipe size (resisting the flow)
And so on..
With a load sensing pump we sense a change of pressure (due to change in load) across the control valve and the pump will automatically respond and make corrections to maintain Delta P. This pressure adjustment can only be achieved by adjusting the pump flow. .
This is why we say pumps produce flow not pressure but they are designed to take pressure
Flow is the desirable product we want from the pump and it is important that we make the pump strong enough to resist any restriction of that flow up to a maximum design pressure. After that we will likely cause damage to the pump.
So how does the pressure change within the pump?
1) By increasing pump speed (increasing the flow)
2) Changing the oil (resisting flow)
3) Adding a load (resisting flow)
4) Pipe size (resisting the flow)
And so on..
With a load sensing pump we sense a change of pressure (due to change in load) across the control valve and the pump will automatically respond and make corrections to maintain Delta P. This pressure adjustment can only be achieved by adjusting the pump flow. .
This is why we say pumps produce flow not pressure but they are designed to take pressure
Thursday, 2 June 2011
How would you define a pump?
How would you define a pump?
A very simple question you might think especially for a hydraulic professional.
This was the simple question posed by a young graduate on Linkedin. Over 3 months later with over 100 comments it is still being debated with some veracity.
I was always taught that pumps produce flow and pressure is a restriction of flow. A challenge to that view is that there must be a force or pressure to move any mass, therefore fluid being a mass means that if there is flow from a pump there must be pressure. I have to agree to this observation and is irrefutable.
So why don’t hydraulic people acknowledge this pressure when we know that there must be some pressure , no matter how small?.
Some things we are taught are often accepted without challenge because with a subject like hydraulics at the beginning one is trying to cope with the overall understanding without thinking of challenging the basics. These concepts eventually become accepted and fixed in one’s own mind until one day someone challenges that view.
I will give you my opinion why we ignore/deny that pumps produce pressure. I believe that by acknowledge this inbuilt load/pressure in our” definition of a pump” will it make the concept clearer or more confusing especially to those with little knowledge of the subject? I believe the latter but more than that what extra benefit does it provide to the hydraulic engineer? I suspect very little.
We know that pumps have different efficiency values. We acknowledge this in our pump power calculations. No pump is 100% and it will be reduced by friction in bearings, running gear and of course the energy needed to push the oil through the pump (also leakage). In hydraulics we factor this into our calculations and because it is a relatively small force value we often tend to ignore it. Remember that hydraulics is used to move or rotate very large loads and as a percentage of these loads the force to push the oil through the pump is very small indeed.
In future then, now that I have given more thought to this issue, how will I describe a pump? I will likely make some adjustments based on whom I am speaking to. Those starting out in hydraulic or struggling with very basic knowledge I will stick to “pumps provide flow” and for those that require a more precise definition: “A pump is a device that forces fluid through its mechanical parts to produce flow” This is wordier but I think a more accurate definition but not sure that it changes much!
Very best
Bob
A very simple question you might think especially for a hydraulic professional.
This was the simple question posed by a young graduate on Linkedin. Over 3 months later with over 100 comments it is still being debated with some veracity.
I was always taught that pumps produce flow and pressure is a restriction of flow. A challenge to that view is that there must be a force or pressure to move any mass, therefore fluid being a mass means that if there is flow from a pump there must be pressure. I have to agree to this observation and is irrefutable.
So why don’t hydraulic people acknowledge this pressure when we know that there must be some pressure , no matter how small?.
Some things we are taught are often accepted without challenge because with a subject like hydraulics at the beginning one is trying to cope with the overall understanding without thinking of challenging the basics. These concepts eventually become accepted and fixed in one’s own mind until one day someone challenges that view.
I will give you my opinion why we ignore/deny that pumps produce pressure. I believe that by acknowledge this inbuilt load/pressure in our” definition of a pump” will it make the concept clearer or more confusing especially to those with little knowledge of the subject? I believe the latter but more than that what extra benefit does it provide to the hydraulic engineer? I suspect very little.
We know that pumps have different efficiency values. We acknowledge this in our pump power calculations. No pump is 100% and it will be reduced by friction in bearings, running gear and of course the energy needed to push the oil through the pump (also leakage). In hydraulics we factor this into our calculations and because it is a relatively small force value we often tend to ignore it. Remember that hydraulics is used to move or rotate very large loads and as a percentage of these loads the force to push the oil through the pump is very small indeed.
In future then, now that I have given more thought to this issue, how will I describe a pump? I will likely make some adjustments based on whom I am speaking to. Those starting out in hydraulic or struggling with very basic knowledge I will stick to “pumps provide flow” and for those that require a more precise definition: “A pump is a device that forces fluid through its mechanical parts to produce flow” This is wordier but I think a more accurate definition but not sure that it changes much!
Very best
Bob
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