Bird
Epic Contributor
Now that makes sense, Boots. Thanks.
Bird
Bird
Hyd Accumilator
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Roy
Platinum Member
Very well put, Scruffy. There are simple accumulators, and there are more complex ones. In the simplest form, a standpipe (fluid at lower, trapped air under normal system pressure at top) provides the shock absorber (for peaks) and the reserve (for low). These things are so effective that they are used in the hydraulics of some aircraft. And no, I wouldn't want to open one up unless I suspected a problem. Reservoirs, with maintenance caps, are made to be routinely opened (reseal-able). Accumulators, typically, are not (at least in the systems that I have engineering access to, which are not tractors).
scruffy
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Roy, Boots, and Bird, I think I have a good picture of what the accumulator does, but I have never run into one that I can recall. I guess I have always had the low-end stuff! Hydraulics and I are no more than strangers passing in the night so to speak...I will pay more attention in the future, and see if I can find one in action! It's got my curiosity up.
Mike H
Silver Member
To embellish a little on some previous posts:
Hydraulic accumulators store fluid under pressure. Most accumulators use volume of gas (air or nitrogen) as the energy storage medium. There are basically three types. Spring accumulators where oil pressure pushes on a piston which compresses a mechanical spring. Bladder accumulators where the gas and fluid are separated by a flexible bladder. And self-displacing cylindrical accumulators which are essentially hydraulic actuators with gas on one side of the piston and the fluid on the other.
They are used for lots of different things. In my area of the country, every residential well has a 10-50 gal blue tank with it - it's an accumulator. They're used to supply hydraulic pressure in missiles. They're used to dampen pump ripple and suppress pressure surges in many types of hydraulic systems. They supplement pump output for short term demand surges.
Hydraulic accumulators store fluid under pressure. Most accumulators use volume of gas (air or nitrogen) as the energy storage medium. There are basically three types. Spring accumulators where oil pressure pushes on a piston which compresses a mechanical spring. Bladder accumulators where the gas and fluid are separated by a flexible bladder. And self-displacing cylindrical accumulators which are essentially hydraulic actuators with gas on one side of the piston and the fluid on the other.
They are used for lots of different things. In my area of the country, every residential well has a 10-50 gal blue tank with it - it's an accumulator. They're used to supply hydraulic pressure in missiles. They're used to dampen pump ripple and suppress pressure surges in many types of hydraulic systems. They supplement pump output for short term demand surges.
Anonymous Poster
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How do these small accumulators provide large volumes of fluid on demand. Theyre not physically large enough to hold large volumes of anything. Like I said, they typically reduce pressure spikes, at least in the power industry involving high pressure fluids.
Just had to throw another 2 cents in
Greg H
Just had to throw another 2 cents in
Greg H
Roy
Platinum Member
Greg; On most systems, they don't have to hold much. Most systems (fluids, electrical, etc.) have constant harmonic distortions. That is, for example, a given system may run at 200 psi, but at any given moment in time, may run +/- 5%. These are the spikes and valleys they protect against (smoothing). For large failures, mission-critical systems/subsystems (think of warbirds, not tractors) they would always have a complete backup system/subsystems (redundant components often using differing technologies) and automatic cut-over. So, in a plane enough reserve to power the system, yes. In a tractor, no.
TomG
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I'm not sure I've heard an explanation I can quite grab on to, but I'm open to having my thinking shaped up.
I think the main purpose of a well pressure tank is to keep from having to run the pump each time the water is turned on. I think most peoples' pumps are capable of supplying about as much water as demanded.
Unlike well pumps, I believe, all tractor hydraulic pumps run continuorsely. A constant displacement pump, used with open centred systems, circulates oil continuously. The volume of oil is affected only by engine rpm.
I'm trying to figure how something the size of what's being talked about would greatly increase cycle time. There's quite a bit of oil in a cylinder, say 3" x 3' and I think a pressure tank would have to be pretty big to make much difference.
What I think would happen unless the tank oil is large in comparison to the demand is that when a valve first opened, oil pressure would decrease, and a pressure tank would supply oil to the cylinder. However, the gas pressure in the pressure tank would rapidly decrease, and so would the oil pressure. The lift would slow or stall when the pressure became less than required for the weight lifted. The lift would start again only when the pump deliveres enough oil to restore the pressure. However, the lift would start slow, because the pressure tank would have to be re-pressurized.
I'm not sure I've heard an explanation I can quite grab on to, but I'm open to having my thinking shaped up.
I think the main purpose of a well pressure tank is to keep from having to run the pump each time the water is turned on. I think most peoples' pumps are capable of supplying about as much water as demanded.
Unlike well pumps, I believe, all tractor hydraulic pumps run continuously. Constant displacement pumps, used with open centred systems, circulate oil continuously. The volume of oil is affected only by engine rpm.
I'm trying to figure how something the size of what's being talked about would greatly increase cycle time. There's quite a bit of oil in a cylinder, say 3" x 3' and I think a pressure tank would have to be pretty big to make much difference.
If a pressure tank was not large enough to support and entire cycle, then I think is that when a valve is opened, oil pressure would decrease, and the pressure tank would supply oil to the cylinder. However, the gas pressure in the pressure tank would decrease, and so would the oil pressure. The lift would slow or stall if the pressure became less than required for the weight lifted. The lift would start again only when the pump delivers enough oil to restore the pressure. However, the lift would start slow, because the pressure tank would have to be re-pressurized. I suspect that variable lift would not be good in tractor hydraulic systems
This 'slow to fast' lift would become more pronounced with larger pressure tanks unless that tank is large enough to support all possible demands. I think that tractor hydraulics are characterized by moderate sized pumps that support fairly lengthy and unpredictable demands. If demands can't be predicted, than a pressure tank could become depleted, and a depleted pressure tank would demand much of a pump's output. It wouldn't be great to have a load from a dock tilt onto a loader when pressure tank is depleted. On the other hand, I can see an advantage to having some dampening in the system. It might be good for steering, components might last longer, and hoses might be less likely to rupture.
I think the main purpose of a well pressure tank is to keep from having to run the pump each time the water is turned on. I think most peoples' pumps are capable of supplying about as much water as demanded.
Unlike well pumps, I believe, all tractor hydraulic pumps run continuorsely. A constant displacement pump, used with open centred systems, circulates oil continuously. The volume of oil is affected only by engine rpm.
I'm trying to figure how something the size of what's being talked about would greatly increase cycle time. There's quite a bit of oil in a cylinder, say 3" x 3' and I think a pressure tank would have to be pretty big to make much difference.
What I think would happen unless the tank oil is large in comparison to the demand is that when a valve first opened, oil pressure would decrease, and a pressure tank would supply oil to the cylinder. However, the gas pressure in the pressure tank would rapidly decrease, and so would the oil pressure. The lift would slow or stall when the pressure became less than required for the weight lifted. The lift would start again only when the pump deliveres enough oil to restore the pressure. However, the lift would start slow, because the pressure tank would have to be re-pressurized.
I'm not sure I've heard an explanation I can quite grab on to, but I'm open to having my thinking shaped up.
I think the main purpose of a well pressure tank is to keep from having to run the pump each time the water is turned on. I think most peoples' pumps are capable of supplying about as much water as demanded.
Unlike well pumps, I believe, all tractor hydraulic pumps run continuously. Constant displacement pumps, used with open centred systems, circulate oil continuously. The volume of oil is affected only by engine rpm.
I'm trying to figure how something the size of what's being talked about would greatly increase cycle time. There's quite a bit of oil in a cylinder, say 3" x 3' and I think a pressure tank would have to be pretty big to make much difference.
If a pressure tank was not large enough to support and entire cycle, then I think is that when a valve is opened, oil pressure would decrease, and the pressure tank would supply oil to the cylinder. However, the gas pressure in the pressure tank would decrease, and so would the oil pressure. The lift would slow or stall if the pressure became less than required for the weight lifted. The lift would start again only when the pump delivers enough oil to restore the pressure. However, the lift would start slow, because the pressure tank would have to be re-pressurized. I suspect that variable lift would not be good in tractor hydraulic systems
This 'slow to fast' lift would become more pronounced with larger pressure tanks unless that tank is large enough to support all possible demands. I think that tractor hydraulics are characterized by moderate sized pumps that support fairly lengthy and unpredictable demands. If demands can't be predicted, than a pressure tank could become depleted, and a depleted pressure tank would demand much of a pump's output. It wouldn't be great to have a load from a dock tilt onto a loader when pressure tank is depleted. On the other hand, I can see an advantage to having some dampening in the system. It might be good for steering, components might last longer, and hoses might be less likely to rupture.
Anonymous Poster
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Sounds like there are different kinds of accumulators,and different uses. That is why I read this , I continually learn something new. Keep up the good info
Greg H
Greg H
Boots
Bronze Member
Maybe the well tank was a bad example. I guess I was trying to make my point more understandable. I'll just give an example of the application of one of these in use in a non tractor related application. The principle is the same. Anyway, here goes.
Out at work we have a hydraulic system with two 8" cylinders approximately 5 feet long. If my math is right, and I'll attempt to NOT use 'fuzzy' numbers, the volume for the two cylinders is about 26 gallons. We need to go full stroke with these cylinders in about 30 seconds which in turn requires a flow of 52 gpm. Our hydraulic pump is rated at only 14gpm at rated pressure which isn't enough to meet the need. So how is the fast stroke time accomplished you ask?
A bank of five accumulators about 6 feet tall and 8 inches in diameter provides the extra flow of pressurized fluid that is needed. The fluid flow's out of these 'Tanks' when needed and supplements the fluid coming from the pump. Added together, there is enough flow to stroke the cylinders as quickly as needed.
The reason for this setup. It's cheaper to buy and operate a small hydrraulic pump and install an accumulator than it is to get a pump that will deliver the maximum flow needed in your system for a short time.
Wow, is all that boring or what? Maybe it can be related back to tractors. Also, it does serve the purpose of helping to cotrol pressure changes since oil like water is basically incompressible, but that is not the primary purpose. The primary purpose of the accumulator is to Accumulate!
Boots
Out at work we have a hydraulic system with two 8" cylinders approximately 5 feet long. If my math is right, and I'll attempt to NOT use 'fuzzy' numbers, the volume for the two cylinders is about 26 gallons. We need to go full stroke with these cylinders in about 30 seconds which in turn requires a flow of 52 gpm. Our hydraulic pump is rated at only 14gpm at rated pressure which isn't enough to meet the need. So how is the fast stroke time accomplished you ask?
A bank of five accumulators about 6 feet tall and 8 inches in diameter provides the extra flow of pressurized fluid that is needed. The fluid flow's out of these 'Tanks' when needed and supplements the fluid coming from the pump. Added together, there is enough flow to stroke the cylinders as quickly as needed.
The reason for this setup. It's cheaper to buy and operate a small hydrraulic pump and install an accumulator than it is to get a pump that will deliver the maximum flow needed in your system for a short time.
Wow, is all that boring or what? Maybe it can be related back to tractors. Also, it does serve the purpose of helping to cotrol pressure changes since oil like water is basically incompressible, but that is not the primary purpose. The primary purpose of the accumulator is to Accumulate!
Boots
Roy
Platinum Member
Finally… On and off, I have been looking for some publicly accessible document or page
Nutshell version… one from Bosch (a South African supplier, not the automotive): http://www.aquapower.co.za/accumula.htm: "Accumulators: Used in high pressure hydraulic systems, perform two functions: they store energy and smooth out pulsations in a system. Bosch offers two kinds of accumulators: Bladder and Diaphragm. Both provide a quick response for a power demand." (Note, although they offer 2 kinds, not to be read as there are only 2 kinds.)
A more detailed version: Industrial Technology magazine: http://www.industrialtechnology.co.uk/1999/feb/parker.html
Bottom line, everything posted in this thread is correct. Just depends on what system your are dealing with, and what the perspective is!
<P ID="edit"><FONT SIZE=-1>Edited by Roy on 10/12/00 12:46 PM.</FONT></P>
Nutshell version… one from Bosch (a South African supplier, not the automotive): http://www.aquapower.co.za/accumula.htm: "Accumulators: Used in high pressure hydraulic systems, perform two functions: they store energy and smooth out pulsations in a system. Bosch offers two kinds of accumulators: Bladder and Diaphragm. Both provide a quick response for a power demand." (Note, although they offer 2 kinds, not to be read as there are only 2 kinds.)
A more detailed version: Industrial Technology magazine: http://www.industrialtechnology.co.uk/1999/feb/parker.html
Bottom line, everything posted in this thread is correct. Just depends on what system your are dealing with, and what the perspective is!
<P ID="edit"><FONT SIZE=-1>Edited by Roy on 10/12/00 12:46 PM.</FONT></P>