Guidelines for placement of a hydraulic cylinder 3

[ayoung802]

This is my first post so thank you in advance for all replies.

I've delt with fixed hydraulic cylinders before at my previous job, but at my current job things are a bit different. In short I'm using hydralic cylinders to open hatches on a boat, so both ends have a free rotating clevis. Besides making sure you have a big enough cylinder and a long enough stroke to accomplish the task is there any guidelines I should follow when determineing the attachement point on the hinge and the attachment point on the structure?

My initial thought is as long as the force isn't applied directly towards the rotating point it should work just fine. Is there anything else I should consider? I want the hatch to operate smoothly.

Thanks again

 

[kchan711]

Hi,

I'm not exactly clear of your design problem. Are these actuated hydraulic cylinders, or are they passive with the help of a person?

In the passive case, a familiar design concept is that of a hood of a car's engine department. Most newer vehicles have a hydraulic cylinder to raise (once given a nudge) the hood and keep it stationary. You could simply mimic the design for your own purposes.

In the actuated case, it's mainly important to consider the load requirements, which will determine the location of the hydraulic force you apply and the magnitude needed to get the job done. If these are personnel hatches, opening time/closing time, structural stability and accessibility will all be part of your design constraints and the location of the hydraulic cylinder.

Hopefully this leads you down the right direction.

Kyle

Kyle Chandler

http://www.chiefengineering.net

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[IceStationZebra]

A couple of points.
- Be careful using the cylinder to limit the hatch travel. Unless specifically designed, cylinders are not generally meant to handle these potentially high stresses.
- Ideally the rod will be fully retracted for most of its life. This will help prevent corrosion of the chrome, especially in a marine environment.
- If you are using an off-the-shelf clevis you may want to consider holding the pin relative to the clevis to minimize wear due to rotation. You can easily put a sleeve bearing in the mating part. Many ag applications run steel on steel, so it really depends on how often it will be used and how long this has to last.
- Speaking of ag, they have many "standard" tie-rod cylinders available relatively cheap with bores up to 5".

ISZ

 

[carnage1]

I found a nice calculation for doing exactly this application on a gas spring vendors website. I don't remember which one though.
As for the attachment point on the moving portion consider your basic bending moment diagram, while it may be easiest to just attach to the end this would not be your strongest option. usually either 1/3 or 2/3 of the total distance is your best option.
For the end near the hinge just break your force vector into components along the hatch and perpendicular to the hatch at fully open and fully closed. This should give you everything you want to know.
except for the retracted and extended lengths but those are simple to figure out.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[ayoung802]

Thank you so far. To clearify the design problem the hatch is actuated hydraulicly. So there should be nothing more then the user pushing a button to open it or close it. I have attached a picture to give you some what of an idea.

Kyle you said the forces should determine the location, is that under the assumption that the cylinder has a limited force because I have yet to select the cylinder size or pump size.

Thank you,
Andrew

 

[kchan711]

Hi Andrew,

I'm not familiar with all of the design details, but, yes, your hydraulic cylinder will have a limited force controlled by its size and the pump size.

Two choices:

1. You determine the load locations on the hatch and frame. Then, based on the weight from the hatch and opening characteristics you need, you spec the proper hydraulics to get the job done.

2. You spec the hydraulics first based on what you feel is necessary, then determine the proper mounting location on the hatch and frame to allow the mechanical advantage of the hydraulic cylinder to open the door.

For instance, we look at a steel plate hinged on one side. If I lift it from the opposite side, it will be easier than lifting in the middle. You're effectively increasing your torque arm. However, there are other constraints that apply. If I want it to open faster with a shorter cylinder stroke, I'll attach the lift point closer to the hinge. But, with that closer attachment, I'll need a greater force from the cylinder stroke to apply the same torque I would have from the end of the plate.

Let me know if I can be of anymore help.

-Kyle

Kyle Chandler

http://www.chiefengineering.net

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[ayoung802]

Thank you all. Everyone made valid points I just wanted a second, third and even forth opinion. Hey why not.