Flap Valve Opening - Rope Tension and Anchor Pull Out Force

[RandomUser_87]

Hi everyone,

I have attached a sketch which may help understand the question I have.

I have a hinged flap which hangs vertically (hinge at top). The flap weight is 10kN and it is 1.8m tall (uniform mass). At the bottom of the flap is a lifting eye.

2.5m away and 0.3m above height of the hinge is an anchor bolt, to which i will connect a lifting block. I then intend on lifting the flap with a single rope through this block.

The question I have is, the anchor bolt is rated to 40kN pull out force so I would like to see what
a) the pull out force will be on the anchor bolt when the flap is open 30deg
b) what the tension is in the rope at the same angle.

The calcs are just to give a ballpark figure for now and will be determined by a supplier later. I would just like an indication of what lifting gear will be required.

I have looked through previous questions and a lot seem to relate to a horizontal flap being lifted and i am struggling to get my head around things when rotated 90deg.I assume that tension is zero when the flap is just hanging down on its own and is a maximum when the flap is fully open (90deg) but I am struggling to make this work.

Thanks for you help.

 

[Dr.D]

Is there any load against the flap when in is vertical (such as impounded water?)? In any case, this is nothing more than a statics problem. Where is the difficulty?

 

[Nidum]

The cable may not be connected to the flap at the ideal position . There could be significant advantage in moving the connection point up some way from the bottom edge . Exactly where you can determine from a scale drawing showing the line of pull of the cable at start , middle and end of lift .

 

[RandomUser_87]

Is there any load against the flap when in is vertical (such as impounded water?)? In any case, this is nothing more than a statics problem. Where is the difficulty?

You are correct it is a simple statics problem, unfortunately its been quite a while since high school. But my assumption is to resolve the moments about the pivot to determine the tension force required for equilibrium. Then to resolve the tension force to determine the horizontal/pull out force?

Unfortunately the angles have me a little confused and I am unsure what is really happening as the angle increases (and ultimately approaches 90deg.

View attachment 214272

The cable may not be connected to the flap at the ideal position . There could be significant advantage in moving the connection point up some way from the bottom edge . Exactly where you can determine from a scale drawing showing the line of pull of the cable at start , middle and end of lift .

This is a very good point, the flap valve has not been installed yet so the attachment positioned might be better located further up the valve if need be.

 

[JBA]

From the diagram shown, I would caution about moving the cable connection to the flap higher. While this would improve the pulling angle early in the lift, it would also reduce the distance between the CG of the flap and the connection point thereby reducing the mechanical advantage at the closed position and all additional lifted points of the flap; and, as the flap approaches 90° it results in an increased angle between the pulling line and flap at the point of maximum weight effect of the flap.

 

[RandomUser_87]

Thanks for the replies everyone,

Before I go further and look at moving the anchor position the flap is lifted from, could someone please sense check my calc on the Tension, T in the rope at a small opening angle, the Tension seems to be quote low for me (approx 1.5kN to open a 10kN valve 15degrees).

I have calculated the moments by resolving for the vertical and horizontal, but I seem to recall a way to find the angle of the moment lever, making the calc a bit easier. Any feedback would be appreciated.

Thanks

 

[JBA]

After some consideration, I am attaching an alternate method of calculation that results in a bit higher T value at the given angles.

 

[JBA]

It has been brought to my attention that some are concerned about the safety of uploaded Excel files; so, to address that concern I have uploaded the below jpeg file showing the above calculation.