# Homework Help: Calculating whether the force of a flow rate is sufficient to move a disc

1. Aug 9, 2012

### MVPhysics

1. The problem statement, all variables and given/known data

There is a vertical 10 inch pipeline with a disc hanging in it. The disc weighs 7.3 kg. There is a flow coming from the opposite direction (water with density 1017.17 kgm/m3) coming at 2250 gpm at 198 psi in the opposite direction (moving up through a pipe). Is there sufficient force to open the free hanging disc? What is the minimum flow rate (in gpm) needed to raise the disc? Delta P is 5 to 7 psi.

b. how about 1680 gpm at 122 psi ?

2. Relevant equations

None provided, but equations used below.

3. The attempt at a solution

First I calculated the Force of the disc which would be 7.3kg (9.81 m/s2) = 71.613 kg m/s2

The flow rate of 2250 gpm was converted to 0.142 m3/s

0.142 m3/s * 1017.17 kg/m3 = 144.43 kg/s

The area of the pipe is A=∏r2 , so 78.5398 in2 or 0.05067 m2

I am not sure what the next step would be in comparing a Force (exerted by the disc and gravity) to the Force exerted by a flow rate.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited: Aug 9, 2012
2. Aug 9, 2012

### voko

What is the dynamic pressure of the flow? What should it be to open the disk?

3. Aug 9, 2012

### MVPhysics

The delta P is 5 to 7 psi. and the piping is ASME Class150, so the pressure would never exceed 290 psig in the pipe. The only effects on the disc is gravity.