# Pressure laws - how hydraulic rams work

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Posted (edited)

I don't know why this isn't making sense to me, maybe I'm burned out.

The idea is this: a pump rated to 1,000 psi. A cylinder head of 100 sq inches. That cylinder can move 100,000 lbs.

What prevents the same tiny 1,000 psi pump from moving a 1,000 sq inch cylinder head, a 1million^2? An infinitely sized cylinder head with any amount of weight on it?

The goal of this question is I want to determine what is more efficient to provide pressure onto my hydraulic ram. Basically how to design the darned thing with the pump in mind. If my pump can do X then I can have an X-sized cylinder head.

Would I ever want my pump to do 1/2X but my cylinder head be 4X in size?

Things of that nature.

Edited by DeepSeaBase
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33 minutes ago, DeepSeaBase said:

I don't know why this isn't making sense to me, maybe I'm burned out.

The idea is this: a pump rated to 1,000 psi. A cylinder head of 100 sq inches. That cylinder can move 100,000 lbs.

What prevents the same tiny 1,000 psi pump from moving a 1,000 sq inch cylinder head, a 1million^2? An infinitely sized cylinder head with any amount of weight on it?

The goal of this question is I want to determine what is more efficient to provide pressure onto my hydraulic ram. Basically how to design the darned thing with the pump in mind. If my pump can do X then I can have an X-sized cylinder head.

Would I ever want my pump to do 1/2X but my cylinder head be 4X in size?

Things of that nature.

I can't do this in these silly units, but if the pump can generate a certain pressure you just need to make sure your system does not require a greater pressure to lift whatever it is you want to lift. Force is pressure x area, so with enough area you can produce any force you want. The catch of course is the rate of lifting, in terms of vertical distance lifted, goes down as the area goes up, because the pump can only introduce fluid at a fixed rate, so the bigger the area the slower it lifts.

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Posted (edited)
46 minutes ago, exchemist said:

The catch of course is the rate of lifting, in terms of vertical distance lifted, goes down as the area goes up, because the pump can only introduce fluid at a fixed rate, so the bigger the area the slower it lifts.

But the prime mover has an area and the lifting piston has an area. What is their relationship to each other that we need more powerful pumps? Can a 1 psi pump lift 1,000,000 pounds if I just have a piston that is 1,000,000 sq. inches?

Edited by DeepSeaBase
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I unfuzzied my head with a long walk, so I can better ask my question:

For a given pressure of the prime driver, to increase the final pressure at the end of a hydraulic ram, do all I need to do is increase the cylinder head size?

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The pressure is the same. Increasing the area increases the force, but since energy is conserved, lifting with a 10x larger force happens at 1/10 the rate.

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I'd like to recommend SI units. Not just for my personal interest (never lived in the US) but also for yours. SI units do bring simplicity and are the units of engineering and science. I even switched from mm2 and MPa, which  used for mechanical engineering, to m2 and Pa when I began computing resonant frequencies, for mechanical engineering too.

So 1000 psi are about 69bar=6.9MPa. That's not much. Hydraulic parts are commonly designed for 21MPa, 35MPa, less commonly 70MPa and 150MPa. You get all seals, dynamic too, and pumps etc up to 350bar anywhere. For 1500bar, you still get static seals from the catalogue.

Beyond that (I made apparatus at 350MPa), you must make your seals yourself, which is really difficult. All parts deform a lot too.

You get good forces from 35MPa already. Have a look at any crane or truck, the hydraulic cylinders are small, often at unfavourable angles, and they move big weights.

Big piston areas are possible. I worked with D=0.4m to create a few MN. Far bigger exists. One serious difficulty is to close the cylinder head: you must exert a force bigger than what the hydraulic pressure will. If not, the pressure just deforms the screws and other parts, creates a slit under the head, and your seal gets extruded through the slit - impressive, and nice result. But just exerting such a force is a challenge, since the screws take already the whole cylinder circumference, so more force needs bigger screw diameter, but these can't be tightened by hand. Up to D=16mm you can, with a 1m long wrench, and you obtain 100kN per screw. Beyond, you need other tools, like a geared wrenched (English name may differ).

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Posted (edited)
14 hours ago, DeepSeaBase said:

I unfuzzied my head with a long walk, so I can better ask my question:

For a given pressure of the prime driver, to increase the final pressure at the end of a hydraulic ram, do all I need to do is increase the cylinder head size?

Are we all barking up the wrong tree because of your initial choice of term for the machine you have mind?

Are you perhaps thinking of a hydraulic intensifier: https://en.wikipedia.org/wiki/Hydraulic_intensifier ?

Edited by exchemist
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18 hours ago, DeepSeaBase said:

What prevents the same tiny 1,000 psi pump from moving a 1,000 sq inch cylinder head, a 1million^2? An infinitely sized cylinder head with any amount of weight on it?

In principle, nothing.
Three will be limitations due to strengths of materials.

The big difference is that the same amount of pumping will only move a big piston by a small distance.

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Posted (edited)
On 5/8/2021 at 5:46 AM, Enthalpy said:

Beyond that (I made apparatus at 350MPa), you must make your seals yourself, which is really difficult. All parts deform a lot too.

So Mr. Enthalpy would you say there's "promise" to using the pressures of the ocean (as in my DAC thread) because of the simplification of the device?

I figured seals to the hydraulic device would be a critical fail point but because I read about very high pressure devices I figured those fail points were much of a hurdle. But for the scales of creating gigapascals it does seem this is a critical hurdle.

A deep ocean device may not have as much pressure from its primary mover (in this case the ocean) at just 110MPa, but the device can be as simple as a large block of metal holding back the ocean on one side and 1atm (101,352 pascal?) on the other side. Put something between that block of metal and you get however much force it applies based on the difference of the area exposed to the ocean versus the area the block is pressing against in the diamond anvil cell.

Such a device doesn't have as many fail points because at some point the-metal on metal contact becomes its own seal (gasket).

That's the only justification I can come-up with so far and I realize it's really reaching into the realm of science fiction and quite a stretch. But, maybe it's a useful application of deep ocean pressures?

On 5/8/2021 at 5:46 AM, Enthalpy said:

Big piston areas are possible. I worked with D=0.4m to create a few MN. Far bigger exists. One serious difficulty is to close the cylinder head: you must exert a force bigger than what the hydraulic pressure will. If not, the pressure just deforms the screws and other parts, creates a slit under the head, and your seal gets extruded through the slit - impressive, and nice result. But just exerting such a force is a challenge, since the screws take already the whole cylinder circumference, so more force needs bigger screw diameter, but these can't be tightened by hand. Up to D=16mm you can, with a 1m long wrench, and you obtain 100kN per screw. Beyond, you need other tools, like a geared wrenched (English name may differ).

See this fascinates me because a deep ocean item can theoretically do this with NONE of those issues you described. In a very simplified form...all you need is a block of metal (cylinder) pressing against another block of metal (pressure hull).

That's it...you don't need a cylinder head to match the pressures of the pump, you don't need screws, you need nothing but that....

And when you want to turn it off...you close the hatch. If the hatch is also a pressure hull...it's like shutting a valve and all the pressure is gone from the system, all of it.

If you want to elaborate on that last part just look at how torpedo tubes function. They are quite simple devices even though there is still complexity to them.

The simplification of the device makes sense to me, but how to describe the technical comparison to the performance of existing machinery makes no sense to me.

I just can't figure out how to show that 110MPa pressure over a simple cylinder head is superior to whatever pump-performance and hydraulic performances we have today. By the numbers it's not superior. It's only superior if its more easily scaled with less problems of design.

On 5/8/2021 at 6:31 AM, exchemist said:

Are you perhaps thinking of a hydraulic intensifier: https://en.wikipedia.org/wiki/Hydraulic_intensifier

Not quite.

That device is in part what I'm describing. But what I'm ultimately describing is a target being pressed upon by a primary driver...the driver could be a 1,000 x 1,000 x 1,000 meter cube of uranium.

All I'm trying to do is compare the primary driver to the target. To quantify it in a way that I better understand why we can create a building-sized megawatt consuming 80,000 ton hydraulic press that can lift an aircraft carrier...but it can't press two diamonds together to make metallic hydrogen.

80,000 ton hydraulic press should be 784,480,000 pascals (784.5MPa) per square meter. If we took a pyramid of infinitely strong material and that press pressed all that pressure onto the tip no bigger than 1mm^2 shouldn't it therefore be 784.5Gigapascals?

Now I realize my managing these ratios is fuzzy, I make errors, but just bear with me.

All I want to know is why creating 100GPa in a diamond anvil cell is consider godlike when we have presses capable of exceeding that by a huge amount?

And I know the answer is in design, cylinder heads, size of equipment, material strengths, I know the reasons are there.

So all I want to know is if we can literally build a block of metal, put an object at the end of it (a diamond) and let the ocean crush it with 110MPa across the entire area of the block....is there a purpose to do so given all the problems of building more complex machines to do it?

Edited by DeepSeaBase
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On 5/10/2021 at 8:07 PM, DeepSeaBase said:

All I want to know is why creating 100GPa in a diamond anvil cell is consider godlike when we have presses capable of exceeding that by a huge amount?

Very few materials we commonly encounter have a structure that is stable under a pressure of 1 GPa. Most, much less.

We do not have presses capable of exceeding 100GPa by a huge amount, because we do not have the commercially available materials to construct such presses. Give or take the odd colliding celestial body. And they are a one shot deal.

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On 5/10/2021 at 2:07 PM, DeepSeaBase said:

If we took a pyramid of infinitely strong material

Would this be made of unobtanium, or impervium?

Infinitely strong or infinitely rigid materials do not exist.

Quote

All I want to know is why creating 100GPa in a diamond anvil cell is consider godlike when we have presses capable of exceeding that by a huge amount?

Citation needed.

Literature I find all say that these high pressures are only achievable with diamond anvil cells.

8 hours ago, sethoflagos said:

We do not have presses capable of exceeding 100GPa by a huge amount

Is a factor of ~7 big enough?

"the researchers investigated the behaviour of the metal osmium at pressures of up to 770 Gigapascals (GPa)"

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3 hours ago, swansont said:

is a factor of ~7 big enough?

"the researchers investigated the behaviour of the metal osmium at pressures of up to 770 Gigapascals (GPa)"

That's actually quite interesting. Thank you +1

Maybe pointing to the rarest naturally occurring element in the universe is stretching the limits of "commercially available" a tad though.

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34 minutes ago, sethoflagos said:

That's actually quite interesting. Thank you +1

Maybe pointing to the rarest naturally occurring element in the universe is stretching the limits of "commercially available" a tad though.

They were doing tests on Osmium (i.e. the device is not made of Osmium), and in any event, Astatine is the rarest naturally occurring element. Osmium is the rarest stable naturally occurring element.

(and commercially available was not one of the claims being addressed)

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