Elevator question - floor return.

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My point is that all of the moving parts (piston, sling cab, etc., all of which move as a single component) do not change weight throughout the travel of the elevator.

It's a matter of volume and displacement, but not of pressure per se. The system pressure does not vary with the stationary position of the elevator in the shaft.

Yes, if you increase the pressure, the elevator will rise, and vice versa. But, with a given moving-parts and load weight, the pressure is the same at any stopped height.
 
LarryFine said:
Yes, if you increase the pressure, the elevator will rise, and vice versa. But, with a given moving-parts and load weight, the pressure is the same at any stopped height.
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Yes, in most hydro elevators the weight of the moving parts always sits on the fluid. You don't, per se, increase the pressure to make it move up, you put more fluid in the cylinder (which requires a pump pressure over that in the cyl.) when the car gets to the right floor, the machine stops pumping and the car stops moving. Also helps to remember that fluids are considered not compressable.

Of course, none of this has anything to with with the original question :D.
 
Just a follow up on some of the questions and comments...

The elevator parks on the 1st floor, and there is a basement/parking garage below it.

It will not freeze here

I understand that home landing can get quite complicated in bigger buildings. Here maybe they just thought it would be best for it to park in the middle so it's closest to every floor, but there is no middle in this case so they chose 1. The building doesn't have many tenants right now and there is lots of construction going on. It seems to be it would be more efficient currently to have the car stay where the last call was.
 
Elevators have to maintain current certifications to be put in operation. At least in my area, that means monthly inspection by a licensed elevator mechanic. Changes to the equipment or operation, requires inspection by a state elevator inspector.

Even something as simple as changing the recall functionality would certainly require a record of the change by a elevator mechanic, and possibly trigger an inspection.

I’d definitely recommend that you not touch it. The liability for you to do ANYTHING to an elevator is quite high.

As far as the pressure thing being discussed; You guys saying it’s the same pressure from top to bottom are forgetting that it’s likely a multiple stage telescoping cylinder and the pressure will increase every time it reaches another stage.
 
Jolted said:
As far as the pressure thing being discussed; You guys saying it’s the same pressure from top to bottom are forgetting that it’s likely a multiple stage telescoping cylinder and the pressure will increase every time it reaches another stage.
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I'm dubious. :unsure:
 
Jolted said:
4 story hydraulic elevator? I know I’ve seen two story ones with single stage, maybe 3 stories. But, 4 stories? That would be a really deep well(s) to drill for the cylinder(s)
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I'm not questioning telescopic elevator jacks; I've seen them. I was an elevator mechanic's helper ways back.

I'm suggesting that it doesn't change my position/opinon that the pressure still won't vary because of their use.
 
LarryFine said:
I'm not questioning telescopic elevator jacks; I've seen them. I was an elevator mechanic's helper ways back.

I'm suggesting that it doesn't change my position that the pressure still won't vary because of their use.
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Oh, well. Then you know more about the elevator stuff than I do. I just watch and ask dumb questions whenever I’m wiring one.

On the hydraulics though, I used to do some hydraulic design work. The force exerted by a cylinder is simply the surface area multiplied by the pressure. Every time a stage reaches the end of its travel and the next smaller stage starts extending, the surface area goes down. If the load remains constant, then the pressure has to go up to compensate.
 
Jolted said:
On the hydraulics though, I used to do some hydraulic design work. The force exerted by a cylinder is simply the surface area multiplied by the pressure. Every time a stage reaches the end of its travel and the next smaller stage starts extending, the surface area goes down. If the load remains constant, then the pressure has to go up to compensate.
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My thinking is that, with a constant-volume pump, the elevator would rise faster with each stage reaching full extension, which I've never seen.

Unless the cylinders were sized so they extend and retract simultaneously.

From Wiki:
In some special applications, a telescopic cylinder is required to extend with a constant force or constant speed. To accomplish this the cylinder is designed so that all the stages extend at the same time. This can also be accomplished in a double acting design by matching the extension and retraction areas of the pistons on all the stages.
 
The deepest elevator shaft that I have drilled was 40 feet deep. It was for a three or four story addition at a hospital.. Drilled a 24" diameter hole, then placed 20" steel casing in it.
 
LarryFine said:
My thinking is that, with a constant-volume pump, the elevator would rise faster with each stage reaching full extension, which I've never seen.

Unless the cylinders were sized so they extend and retract simultaneously.

From Wiki:
In some special applications, a telescopic cylinder is required to extend with a constant force or constant speed. To accomplish this the cylinder is designed so that all the stages extend at the same time. This can also be accomplished in a double acting design by matching the extension and retraction areas of the pistons on all the stages.
Click to expand...

Yes, when the cylinder is moving that would be true. But sitting at rest, the pressure will be higher if a smaller stage is extended.

The cylinders that extend all stages together are mechanical interlocked. That actually makes a lot of sense for an elevator as it would keep the speed constant. I dunno, don’t know that much about elevator jacks.
 
Dzboyce said:
The deepest elevator shaft that I have drilled was 40 feet deep. It was for a three or four story addition at a hospital.. Drilled a 24" diameter hole, then placed 20" steel casing in it.
Click to expand...

Yah. That’s the deepest I’ve ever seen too. I think it was thirty some feet jack for a three story building. Then they have to use a crane to drop the jack in. I’m thinking that any taller than that would get pretty difficult to deal with.

But, don’t they typically get away from hydraulics when it’s much more than 2-3 stories anyway?

I’m just thinking the OP has a four story hydraulic, seems likely that it’s multiple stage.
 
Jolted said:
Yes, when the cylinder is moving that would be true. But sitting at rest, the pressure will be higher if a smaller stage is extended.
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I disagree, for the reasoning already given above. IMHO, it's still only about volume and displacement.

The telescopic sections merely allow the piston to behave as if it was longer (i.e., had greater volume).
 
LarryFine said:
I disagree, for the reasoning already given above. IMHO, it's still only about volume and displacement.

The telescopic sections merely allow the piston to behave as if it was longer (i.e., had greater volume).
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With a loss-free mechanical interlock, a three stage telescoping column behaves as if the piston area is the sum of the three active piston areas, but with a 1:3 mechanical advantage. The net effect is that of single column whose area is the average of the three.
This applies equally well to static and dynamic situations.
 
GoldDigger said:
With a loss-free mechanical interlock, a three stage telescoping column behaves as if the piston area is the sum of the three active piston areas, but with a 1:3 mechanical advantage. The net effect is that of single column whose area is the average of the three.
This applies equally well to static and dynamic situations.
Click to expand...

Do you know if that’s typical elevator Jack design? Seems like the logical way to go, but I don’t think I’ve ever seen one.
 

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