3 replies to this topic

[Sherif Morsi]

Hi,

 

I am currently in technical clarifications regarding a new 3-way globe valve. The valve will have two operating cases:

1- Full flow: Where the fluid flows 100% through the valve without diversion

2- Partial flow: Where 50% of the flow is diverted and the remaining 50% flows through the valve

 

It's a globe valve

 

The vendor has submitted their calculations and came back with Cv bigger than the one I calculated using ISA 75.01.01 (2012). I double checked my calculation using our company's software and all is in line with my calculation.

 

I believe I should accept the vendor's calc. Any thoughts/recommendations?

 

Regards,

Sherif

[Zauberberg]

If you just accept it, then why did you do all that verification work? It can happen sometimes that vendors make mistakes. You can ask them how did they perform sizing of this particular valve and offer them your calculations as a support to your doubts.

 

Double-check your calculations, just to make sure you did it all right.

[SPC]

Hi Please check again Cv for your Valve as follows:

 

Liquid Flow =            N1*  Cv  *  √  Δ P  /  G Liquid Flow = l/min     N1 = 14.42     Δ P = Pressure Difference, bar   G = Specific Gravity  

 

1st case

1) find out Lquid flow for above case

 2) Find Pressure drop across your valve

a) Pressure at Inlet of Valve = Source Pressure - Pressure loss due to flow /Frictional drop - Pressure drop due to any equipment / Filter / strainer etc.)

Pressure at Just Outlet of Valve = Destination Pressure + Pressure loss due to flow /Frictional drop + Pressure drop due to any equipment / Filter / strainer etc.)

Hence, Pressure drop across Valve = Pressure at Inlet of Valve- Pressure at Just Outlet of Valve

   OR 

If valve is installed downstream of Pump, you can calculate Pump Head (in bar) at flow for case-1 & consider Average sp. gravity

 

Do your calculation for 2nd case also.

 

Hope this helps,

 

Regards,

SPC

[Sherif Morsi]

Thanks everyone for the feedback.

 

I did the calc again and it still has the same results. I have scheduled a conference call with the vendor to discuss. Will keep you posted