3 replies to this topic

[riven]

All

 

On plant I have an issue with a rather large valve. Due to a sudden process disturbance (blast furnace slip), the pressure in front of this butterfly valve suddenly increased. In the event of a slip, the valve should immediately fully open. However in this case the valve closed against its mechanical stop resulting in a pressure excursion. Downstream pressure remained constant.

 

There are two theories; poor maintenance of the actuator or under sizing of the actuator (I am also looking at incorrectly sized valve). I have given the manufacture a call who should be able to give me actuator sizing charts but I wanted to check some first principles.

 

To size the actuator I did the following.

Required actuator torque = dynamic torque due to fluid forces + bearing torque + seating torque.

 

Item 2 I have from the valve specification. Item 3 is 0 here as the valve cannot fully close.  Thus I need to calculate the dynamic torque. 

Dynamic force (N) = upstream (dynamic + static) pressure (N/m2) * area of valve (m2)

 

Thus I can get a torque rating for different openings and different pressure events. I can do this by multiplying the above force by the height of the valve.

 

The question; should I be using differential pressure instead of upstream pressure for my calculation?

 

 

Any other comments are appreciated.

Edited by riven, 16 April 2014 - 07:54 AM.

[Shivshankar]

I think so, you can consider differential pressure (Upstream(P1) and Downstream (P2)) in your calculation.

[processengbd]

Hi

I have a general question. How can i find the dynamic pressure upstream of the valve?

[Shivshankar]

Processengbd,

 

Dynamic pressure is nothing but moving flow of fluid and can be expressed in terms of fluid kinetic energy.

 

P = 0.5* ρ*v^2 

 

P = Pressure

 

ρ = Density of fluid

 

v = Velocity of fluid.