How much pressure in PSI was needed in the Ancient World to cut stones?

[philo]

Was watching a video on the the Great Pyramid of Giza and it got me wondering how one might cut one of the stones.

Doing a couple google searches, I thought that a Venturi pump would likely be the means by which the stones were cut. The problem being how would they get a large enough psi through one.

The first thought of mine would be a large and heated container that forces high pressure air into the pump.

The second thought came upon looking at ancient wind catcher systems.

Potentially one could use an ancient wind catcher to grab cool air in the sky, force it below ground, and then through a heated container to generate the necessary high pressure.

Anyone, want to take a stab at writing some calculations on what the potential psi might be?

 

[Baluncore]

Welcome to PF.

Stone particles in water can be very abrasive. Rubbing wet rocks together does not require particularly high technology.

Water jet cutting would require impossibly high pressures.

Saw blades for cutting stone can be made from soft materials like wood or copper. Harder particles that actually do the cutting, become embedded in the softer material, like diamonds in a copper drill tube.

You need to better describe your proposed cutting mechanism.

 

[philo]

Thanks for the welcome.

The mechanism would be akin to something like this video.

Using high psi water stream to cut the stone.

I’d imagine a Venturi pump like this


Finally as the for the air


I’d imagine by hooking up a copper Venturi pump to the Nile, and using some form of high pressurized air potentially from a wind catcher one might be able to generate a water stream with high psi, I’m not sure how high though. Also, it wouldn’t need to be as high as 60k psi, given the time and labor available, I’d imagine you could get a lot done with much smaller psi.

 

[Baluncore]

I’d imagine by hooking up a copper Venturi pump to the Nile, and using some form of high pressurized air potentially from a wind catcher one might be able to generate a water stream with high psi, I’m not sure how high though.

High pressure air is available from a trompe in mountains where it rains. But that is not really applicable to the lower Nile valley.
https://en.wikipedia.org/wiki/Trompe

I hate to pour cold water on your idea, but water jet cutting of rock does require very high pressures, and there must be abrasive powder or particles in the water jet. Limestone and marble are soft rocks, so they could probably be cut more easily with ancient technology.

Rock is usually cut from a face by splitting it with wedges. There are usually large regular horizontal cracks, caused by unloading as the rock above was weathered and eroded. To cut a block to a rectangle of the required size, a line of shallow drilled holes could be opened with tapered wedges. I would expect water was used during the drilling and finishing of the block surfaces.

If the cut building stones were transported along the Nile, then they should have been lashed under a raft, not put on top of an unstable boat. Limestone or marble has a density of between 2 and 2.7, so the weight of a 2.7 T rock would be reduced by buoyancy to only 1.7 T when suspended underwater.

 

[philo]

High pressure air is available from a trompe in mountains where it rains. But that is not really applicable to the lower Nile valley.
https://en.wikipedia.org/wiki/Trompe

https://en.m.wikipedia.org/wiki/Windcatcher
https://en.m.wikipedia.org/wiki/Stack_effect

The 2 articles do more justice than I can to the topic. Windcatchers are native to the area and can generate pressurized wind.

I hate to pour cold water on your idea, but water jet cutting of rock does require very high pressures, and there must be abrasive powder or particles in the water jet. Limestone and marble are soft rocks, so they could probably be cut more easily with ancient technology.

It is appropriate to destroy the idea if it doesn’t work. I’m more of a theorist, and this is more an engineering problem in my opinion.

Using something akin to a windcatcher and a heat source what would the the theoretical highest psi they could get using known technologies at the time?

 

[Baluncore]

Using something akin to a windcatcher and a heat source what would the the theoretical highest psi they could get using known technologies at the time?

Ram air pressure is equal to half the density of air, multiplied by the square of the wind speed. Very windy places have pressures of 80 lbs per square foot. A wind catcher will never generate more than one psi.

 

[Baluncore]

The stack effect might well generate more energy than a wind catcher. If the stack was a thin-wall vertical tube in the sun, then heating the column of air would reduce it's density, so the warmer air would be more buoyant and tend to rise. If the energy was extracted at the bottom of the stack, the pressure difference would be limited to less than the 14.5 psi of atmospheric pressure.

Pressures only rise significantly when the flow of a fluid, usually a liquid, is blocked. The energy involved is equal to the volume of fluid that flows, multiplied by the pressure difference along the flow. Without flow there can be no energy. Without pressure there can be no energy.

Both the wind catcher, and the stack effect, operate with huge volumes of free flowing air, moving through very wide channels with very low pressure differences. Any attempt to significantly raise the operating pressure of a wind catcher will obstruct the flow, so the wind will take another path, for example around the wind catcher.

 

[sophiecentaur]

Engineering was very different then so we can't assume anything about methods 'they' would use.

Is there, in fact, any need for high pressure air? I can't imagine that technology would have been available; leather (possibly lead) tubing would not handle high pressure air but could be suitable for water.

Are we sure that hydraulic cutting was actually used? Skilled use of wedges gives good square-cut blocks from appropriately chosen stone cliffs. Grinding with a round (quorn?) stone (as in grain milling) and plenty of water can give very good results. Also, it would be only the facing stones that would be well finished.

If you take water out of domestic tap (say 1Bar from a 10m head), that is good enough for shifting dirt and cleaning stone slabs with the right nozzle. Added sand would improve the cutting. But the stone quarries would not be down at river level; stone would have been dragged to the river level for finishing. They could have been sited where a reasonable water supply was available. Obvs, the Lower Nile has very little slope so getting a 10m head would involve a long aqueduct from an upstream take-off. Have any been found?

A small water tank could be fed from the river, using a water wheel, Archimedes screw or any other of the methods we see in pictures of ancient Egyptian irrigation methods.

 

[jrmichler]

Engineering was very different then

And there is a good book on the subject. Title is The Ancient Engineers, by L. Sprague De Camp. You can still get a copy: https://www.amazon.com/dp/0345482875/?tag=pfamazon01-20.

From the chapter on Egyptian engineers: