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cargo lift, hyraulic cylinder

cargo lift, hyraulic cylinder

(OP)
i just commissioned a cargo lift with a 3 kw motor , 2400 rpm motor but while working there is a huge sound like a humming sound which seems to come from the cylinder. clueless glasses

RE: cargo lift, hyraulic cylinder

That will be the vibration coming from the pump and or motor. To shut it up, you'll need to attenuate the cylinder to stop it from vibrating.

It could also be that your motor speed is close to the natural frequency of the cylinder. In which case, you'll need to either change the motor speed, get a new cylinder with a different natural frequency or do something drastic to stiffen the cylinder up to move its natural frequency away from the motor speed.

Hpost

RE: cargo lift, hyraulic cylinder

(OP)
dimension of the cylinder is thin which is 35(shaft)x80(cylinder)x 3.50 mts long in closed position.to change the natural frequency , how can i make my cylinder supplier understand it?

RE: cargo lift, hyraulic cylinder

Natural frequency is equal to the square root of the stiffness over the mass. If you can't change the stiffness, change the mass.

The cylinder supplier probably wont help you much, it's not their fault that the cylinder's natural frequency is close to the motor speed.

That is a very slender cylinder, not surprising it's signing. Can you brace it at all in the middle at all?

Does the noise change as the cylinder extends...does it get any more noisy or less noisy?

RE: cargo lift, hyraulic cylinder

I would estimate the frequency of the humming and compare it with the calculated natural frequency of the cylinder and load to see if they could be the same but often they are not. Humming is often 60 or 50 cycle hum. Poorly designed hydraulics systems will have natural frequencies much lower than that.
The natural frequency of the system should be calculated.
On page 2/27 there is the formula for natural frequency.
http://deltamotion.com/peter/Mathcad/Mathcad%20-%2...
The pdf file shows how I can simulate the cylinder with changing load or disturbances and how the closed loop control will react.

My suspicions is that the mechanics are vibrating.

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

RE: cargo lift, hyraulic cylinder

(OP)
the humming sound is more in a down position when the piston is contracting and in a particular position only and also when its extending when we lower the lift that sound is little lessdazed

RE: cargo lift, hyraulic cylinder

Is the cylinder connected to the power unit with hoses or rigid tube?

RE: cargo lift, hyraulic cylinder

(OP)
With hoses

RE: cargo lift, hyraulic cylinder

That suggests that issue is from vibrations transmitted by the oil, rather than structure borne noise.

The pulsations or ripple from the pump are being transmitted to the cylinder via the oil. The frequency of the vibrations is, as stated, close to the resonant or natural frequency of the cylinder. As the issue is more about noise than actual movement, it suggests that it will not take much to reduce the noise.

I think that you best bet is to change the cylinder mass or stiffness. Maybe up, may be down...???

RE: cargo lift, hyraulic cylinder

(OP)
so the vibrations are generated in the power pack , may be the kw for this much long cylinder is not enough? i had beforehand made arrangement for mounting of another pump to so shall i try by putting another pump with 3 kw motor?

RE: cargo lift, hyraulic cylinder

It's not about power, it's the pressure pulsations in the pump that are causing the noise. If you can change the power unit, change the speed of the motor. That will change the frequency of the vibrations.

RE: cargo lift, hyraulic cylinder

(OP)
So if I change the speed ,from 2800 rpm shall I decrease the speed?

RE: cargo lift, hyraulic cylinder

Perhaps..?

Lowering the speed might push it towards the resonance point. Likewise, going up in speed could do the same. Without knowing the natural frequency of the cylinder, it's impossible to know which way to go.

Given the size and shape of the cylinder, my guess would be to go slower.

Slowing the motor down will decrease the flow. You'll need to get a bigger displacement pump to keep the cylinder speed the same.

RE: cargo lift, hyraulic cylinder

(OP)
coming down to the pump there was a provision for one more pump of same size to be put there so , shall i try again to put one more pump with same specification and then reducing the flow of both of them will it work?
or shall i go ahead with changing the piston rod with a more thicker one like from 35 mm to 45 or 50 mm?

RE: cargo lift, hyraulic cylinder

Seems easier to change the rod diameter. If you not concerned with the increase in speed caused by the bigger rod, go for it.

There is no guarantee of success here. you'll have to try it and see what you get.

RE: cargo lift, hyraulic cylinder

Is there a counterbalance valve in the circuit?

RE: cargo lift, hyraulic cylinder

(OP)
finally the problem was solved when another pump was installed in parallel and there is no soundbigsmile still i have the problem of piston swaying up and down mad

RE: cargo lift, hyraulic cylinder

In what orientation is the cylinder installed? Horizontal or vertical?

RE: cargo lift, hyraulic cylinder

(OP)
The cylinder is in vertical position.

RE: cargo lift, hyraulic cylinder

So describe the swaying up and down. What frequency and how much?

RE: cargo lift, hyraulic cylinder

(OP)
its slight when there is too much load or when the lift is on the top position.

RE: cargo lift, hyraulic cylinder

You need to define "swaying" a bit more clearly.

RE: cargo lift, hyraulic cylinder

(OP)
its like jumping it might be due to air in the cylinders for the cylinder never opened to its full stroke and its extra in length.

RE: cargo lift, hyraulic cylinder

(OP)
Still after so long I am having problem with lift swaying up and down, like if a person gets on it jumps it also jumps and the piston rod us moving up and down

RE: cargo lift, hyraulic cylinder

What have you done to get the air out?

Any air in the system will find its way to the under side of the piston head in the cylinder. Air will give you what you are seeing.

RE: cargo lift, hyraulic cylinder

(OP)
we removed the pulley and moved it up and down so that all air comes out as the oil enters the piston from top and moves the piston down , due to the length of piston we could not moved it complete left like 10 cms and when we connected again we still faced the prob

RE: cargo lift, hyraulic cylinder

I'd suggest the following

Lower the cylinder to approx 2" from the bottom position.

Crack the fitting at the bottom of the cylinder, then force cylinder down. It is the air under the piston head that is causing the problem and it sounds like you have bled the top of the cylinder.

It might be messy.

Needless to say, you need to get all of the air out. Otherwise you will have a bouncy cylinder.

RE: cargo lift, hyraulic cylinder

(OP)
It's a single acting piston so the bottom side we are using a hose connection for drain this we have connected to a line which goes to the bottom of oil tank So if remove this drain line will it solve our problem?

RE: cargo lift, hyraulic cylinder

Sorry, I wasn't aware that it was single acting. Not that it changes anything.

In that case, I would suggest letting the cylinder down to the bottom. Crack the fitting at the base and then try to lift the cylinder.

I am sure you will find that the bottom side is the pressure side and the top side is just there to drain away any oil that gets over the seal.

The lift falls under gravity right???

RE: cargo lift, hyraulic cylinder

(OP)
Yeah it falls under gravity as the oil enters from top it's the pressure side and the bottom we were using for dfor passing oil normally we used a air hose but in This case we are using a hose which goes to bottom of tank☺.

RE: cargo lift, hyraulic cylinder

With the rod facing up, the gravity induced load will act on the piston head, creating pressure on the bottom side.

It's a single acting cylinder, the load is raised and lowered by pumping oil into a releasing oil from under the piston head.

It can't be as you say, have another look.

Can you sketch out your understanding of how this thing works???

RE: cargo lift, hyraulic cylinder

Right, now explain 2 things.

1) How do you think the lift goes up?

2) What do you think stops the lift falling under gravity?

Please remember, I am trying to help you here. I am not taking the "P"

RE: cargo lift, hyraulic cylinder

(OP)
the lift goes up when it pulls the rope on a pulley block above it, this piston has a pulley block attached to it too it fall under gravity when we remove the pulley block from the piston and let it go down.

RE: cargo lift, hyraulic cylinder

Now it's clear, there is a rope and pulley. You didn't mention that before.

So, just do the same, but at the other end of the cylinder. The air will accumulate at the top fluid port.

Just to be clear, when you say rope, do mean steel rope?

If it's not steel rope, there will be loads of compliance which could explain why you get this unwanted effect.

RE: cargo lift, hyraulic cylinder

(OP)
dear sir the rope used here is steel rope and there is no slackness in it , its the piston which is bouncing up and downdazed.so the air which is causing problem here has accumulated at the top fluid port and i have to take up and leave like 10 cms and crack it ?

RE: cargo lift, hyraulic cylinder

Yes...do that

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