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# Calculate stress on a Hopper outlet valve3

## Calculate stress on a Hopper outlet valve

(OP)
Dear Engineers,

I have a conical hopper and the outlet diameter is a 1" diameter pinch valve.

Please can you guide me on the formula how much stress/pressure is the 1" diameter pinch valve experiencing when in fully closed position if the hopper is filled with 120Kg of Powder.

The operating pressure of the valve is 1 to 6.5Barg, thus, i would like to calculate what is the maximum powder weight it can operate.

Please refer to attached drawing of the conical hopper.

### RE: Calculate stress on a Hopper outlet valve

For uniform density use simple hydrostatic formula.
Pressure = weight density x total height.

Modify the formula for density as it varies with height.

Ted

### RE: Calculate stress on a Hopper outlet valve

(OP)
Hi Ted,

Thanks for the advise. I was thinking the hydrostatic formula only applies to fluids and not solid? Thanks.

### RE: Calculate stress on a Hopper outlet valve

The force in granular materials can approach zero - they can resist shear and form clumps and bridges over openings. If the hopper is subject to a high vibration those shear forces are eliminated and the granulated material will behave as liquid, which is the maximum force available. The actual force will be between zero and the hydrostatic approximation.

### RE: Calculate stress on a Hopper outlet valve

(OP)
Hi 3DDave,

Thanks for the advise. Vibration of the hopper and opening of the pinch valve will only happen during discharge operation.

I am thinking about during preparation stage whereby the valve is in fully closed position and the hopper is filling up with the powder to be discharged, where the weight of the powder can goes up to 200Kg. Thus, i would like to check if the pinch valve used can withstand such pressure/stress.

### RE: Calculate stress on a Hopper outlet valve

Assuming the material acts as a fluid will give you the worst case pressure. Granular materials with friction can bridge, which only lowers the pressure on the outlet.

### RE: Calculate stress on a Hopper outlet valve

(OP)
Hi Guys,

Thanks for the great advises. I am clear now.

The link that Ted provide is fantastic.

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