Hydraulic lift photo01

Hydraulic lift photo02

I've been trying to understand "pascals principle" and thus far have learned a lot thanks to this forum. I have a few more questions regarding the topic so along the way please correct me if I'm wrong.

I've found this data using a few equations and I'd like to know if there are any differences between these two drawings above? Also the relevant question mentioned in the title. Considering both photo's the fluid volumes, pipe bores, & loads are all of the same dimensions as the hydraulic lift shapes are the only differences.

Using formulas f2 = a2 / a1 and the mechanical advantage ma = f2 / f1 I've found my data as of:

MA = 7

F1 = 507 N or 114 lb Pipe/piston diameter = 3"

F2 = 3,549 N or 798 lb Pipe/piston diameter = 8"

Question: With this data is (f1) required to lift (f2)? Or it required to just be at equilibrium & balance each other out?

If the answer is that it is required to lift (f2) then how do I find out what weight is required to be at equilibrium of the two weights?

Now If the answer is that (f1) is required to be at equilibrium with (f2) is it reasonable to assume that if I added only 1 extra lb to (f1), alike to the "See-Saw Principle" (f2) would then be lifted past equilibrium?


Figure the surface area of a piston (pi times radius squared), then divide the weight on top of it by the square inches of it's surface, this will give the pounds per square inch (PSI) of pressure exerted on the water. Do this on each piston and compare the PSI of each. The piston with greater PSI will push down and lift the piston with lighter PSI. If they are the same, and at the same water level, they will not move (at equilibrium). In the bottom diagram if one piston is higher than the other, then the water pressure, PSI, from the different depth will also be pushing up on the lower piston.

  • $\begingroup$ Thank you. I got (F1 = 16.13 psi) and (F2 = 15.88 psi). Now as you said we must calculate the pressure of the water if one piston is higher than the other. So say the bottom diagram of piston#1 was 10 feet higher than piston #2. Since per foot of water = .433 psi is my calculation correct? 10 x .433 psi = 4.33 psi to the force that piston#1 is giving to piston#2 That's 16.13 psi + 4.33 psi = 20.46 psi. $\endgroup$
    – Rip
    Sep 29 '19 at 22:01
  • 1
    $\begingroup$ @Rip: I haven't done the math but your approach is correct and the numbers seem reasonable. $\endgroup$ Sep 29 '19 at 22:29
  • $\begingroup$ haha thank you again. Because in the bottom diagram the piston is higher & Instead of going into detail I suppose I'll just ask the question must I add .433 psi for each foot of water above the piston? $\endgroup$
    – Rip
    Sep 30 '19 at 0:33
  • 1
    $\begingroup$ @Rip: yes, use the depth difference between the two piston's surfaces $\endgroup$ Sep 30 '19 at 0:45

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