Estimating Hydraulic Push Needs
Estimating Hydraulic Push Needs
(OP)
Hello - On a barge, we are rigging a formerly electric operating A-Frame hoist with two hydraulic cylinders for smoother operation. It must lift from about a 30 degree position (up from horizontal) to slightly past total vertical. The idea is to lift a load through the A-frame, just past vertical for safety and to relieve the cylinders...then the electric hoist will lower the load to the deck. Each 4" x 3/8" thickness square tube A-Frame arm is 14'-6" long and weighs about 500lbs. We would like to lift up to a 5 ton load with the A-frame, so each cylinder should be capable to lift 5,000 lbs each, in theory. However, because the cylinders connecting points at the A-frame arms are 1/3 up from the a-frame deck hinge axel (5 feet exactly), there is extra leverage needed to accomplish the lift. At the lowest postion, the cylinder will be at 90 degrees in relation to the arm and hinge anchored at the bottom clevis. The cylinders would then be at a 45 degree angle in relation to the horizontal barge deck. The ram extension would be 36" to accomplish the total lift / swing. Speed is not critical, but should be at least the 36" in about a minute or less. How much force does each cylinder need to be capable of? Any takers for this question?





RE: Estimating Hydraulic Push Needs
Get out the dynamics text book.
I2I
RE: Estimating Hydraulic Push Needs
Draw out a scale dwg, apply your geometry for the effective distances the loads and cylinders act on (moments about the pivot point on deck) and you will get the maximum cyl force at some pont through the arc.
It's a fairly simple problem, not trying to avoid answering, but if it's beyond your background or training it would be best to have someone locally review it in person. There may be other issues overlooked here that aren't evident on a BB. One thing that comes to mind is counterbalance or overcenter valves on the cylinders to prevent loads running away when it goes past center, or for safety in case of a hose break or accidental valve shifting.
kj
RE: Estimating Hydraulic Push Needs
I2I
RE: Estimating Hydraulic Push Needs
This may be looked at as a torque calculation as you are rotating about the pivot applying forces at several different radii. As above some basic geometry needs applying.
You would also need to know what Factor of safety to apply to this particular device. Being a heavy industrial application be over generous in safety factor for use and abuse. This will also help overcome the acceleration requirement
Simplest is what rating was the electric hoist and did it do the job?
RE: Estimating Hydraulic Push Needs
RE: Estimating Hydraulic Push Needs
RE: Estimating Hydraulic Push Needs
supply a DWG of the geometry and you would get some real answers.
I recommend looking at counterbalance valves mounted directly to cyl ports, (code for lifting around people)
I agree do it hyd both directions
hydroMET
RE: Estimating Hydraulic Push Needs
Can a simple flow control make sure the difference between the applied and load torque will provide the desired angular acceleration? This is not a simple problem.
There has been no mention of a servo controller. I don't see how you can control this with out because of the changes in the required forces/torque due to the changing geometry. A servo controller can also synchronize the two actuators.
The hydraulic system gain is proportional to:
Kvpl*sqrt(Ps*Ape-Fl) A portion of the VCCM formula.
The Fl or load force that the actuators see changes due to the changing geometry so the controller gain must also change as the function of geometry. The controller gain changes inversely as the hydraulic gain changes.
Don't ever use counter balance valves with servo valves and controllers. This is a very common mistake. Use blocking valves that are energized open.
RE: Estimating Hydraulic Push Needs
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Sometimes I only open my mouth to swap feet...
RE: Estimating Hydraulic Push Needs
kcj
RE: Estimating Hydraulic Push Needs
Not a problem. Fantastically accurate servos have been around for years.
I don't think the servo controller is overkill considering the geometry changes. Smooth motion counts for a lot.
RE: Estimating Hydraulic Push Needs
Some had flow dividers, some had proportional controls and some just had directional control valves.
I found that the only way to get truly reliable performance is to use a good flow divider.
1 pump, 1 valve, 1 flow divider and 2 cylinders. That's all it took to keep these things working in all weathers.
Using servo valves is the "sexy" way to do it, a rotary flow divider is the best way!
Hydromech