6 replies to this topic

[sandeep chk]

Can anybody help me out to understand what is meant by"valley angle" of a pyramidal hopper (placed below an ESP). I find it is given that the valley angle should be more than 55 deg with horizontal. Which angle is actually meant by "valley angle"for a hopper?Is there any relationship between valley angle of hopper and angle of repose for the particular dust material?

[Rama]

Dear Sandeep,

The valley angle of a pyramidal hopper is the real angle (with the horizontal) of the edge formed at the corner where the two adjacent sloping sheets of the hopper meet. Even if the sides of the hopper are sloped adequately to discharge the dust, the valley angle will be shallower than either of the slopes of the two side sheets. This results in the build up of dust near and along the valley.

The valley angle can be easily calculated from the geometry of the hopper. If you need help, please hit: http://www.ajax.co.u...ramidHopper.htm - this gives a sketch of the hopper along with the valley angle and a simple on line calculator for the valley angle given the detailed dimensions of the hopper.

Yes, the angle of repose helps in getting an idea of the slope required for the hopper. But it is not exactly the same as the required slope of the hopper. The angle of repose is a function of the inter particle friction, cohesion and the shapes of the dust particles. The slope of the chute or hopper is more a function of the smoothness of the hopper material and the friction between the particles and the hopper material. 55 deg is a commonly accepted (safe) value for most materials. If you have the actual value for (or some experience in handling) the specific material, you may use the known value. (Please note that the values of angles given in the above mentioned reference is with the vertical!)

Hope this helps….

[Andrei]

Very, very good internet link Rama. thank you.
Angle of repose of most of the granulated materials, fairly regular shapes, is 60 degrees. The valley angle of the hopper has to be smaller than this value to avoid bridging. This is the source of 55 degrees value.

[sandeep chk]

Thank you Rama and Andrei for your help.Rama, it is very useful link that you have insdicated.

[Rama]

Dear Andrei,

I think there is some misunderstanding here – unless there is a typo in your post. Most dry materials have angle of repose less than 40 deg. Very few materials have up to 45 deg. In any case if the angle of repose is 60 degrees, the valley angle has to be even larger than 60 degrees, and not 55 degrees. (These angles are measured against the horizontal!)

Manufacturers of conveyors and text books on material handling carry tables of these values for various materials.

- Ram.

[Andrei]

Rama,

You may be right. For sure there is a reference misunderstanding in the middle. My mind works the way portrayed in the drawing from the link you provided, angle is measured with vertical, not horizontal. I am sure we are talking about one and the same thing, but from different viewing angles.

[Rama]

Thanks, Andrei,

I guessed as much. Both of us meant the same thing but were looking from different directions!

Have a nice day.