Pressure Drop Comparison for Globe / Butterfly / Gate & Ball valve

[peter vaf]

Hi,

My question is about the Pressure Drop Comparison curve,which is shown The Min Drop is for Globe type .
However ,at Normally condition Globe type should has a high pressure drop and gate should be less .(Is it only at the Fully opening Condition or at the all condition)?

 

[bcd]

Chart says DP is constant and flow is constant. If so, to get the same pressure drop as a globe, the ball and butterfly valve must be nearly fully closed.

The chart is not showing the pressure drops when the valves are fully open.

 

[peter vaf]

Dear bdc,

Thank you for your reply.
Please confirm in the case of full opening condition, the pressure drops of globe valve is more than all types .

 

[LittleInch]

Of course it is.

So the others when fully open as a full bore valve is basically the same as a pipe.

A globe valve has lots of bends and restrictions.

That graph has nothing to do with it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

That chart shows the pressure recovery of various type valves. So, cavitation issues from worst to best is ball, butterfly, ecc. plug, and globe for the same application.

A gate valve is not shown.

Good Luck,
Latexman

 

[peter vaf]

Yhank you for your complete explaination..

 

[MortenA]

@peter_vaf,

to elaborate a little, the lowest pressure at the vena contractor has a implication if it goes below the vapour pressure, then you will get cavitation in your valve and it will wear out quickly. Its interesting that a ball valve has such a high pressure recovery but you chart is somewhat misleading or can cheat you since it must represent a situation where FLOW is not similar for the various valve type because then, of course, ball valve would have the lowest total dP of the four types.

So you will rarely see cavitation in a fully open ball valve - but i guess the chart also add to the explanations as to why you dont use a ball valve for flow control if you can avoid it.

Best regards, Morten

--- Best regards, Morten Andersen

 

[peter vaf]

In this regard,I am not sure about possibility of replacement of Segmented Ball Valve with Glove type in order to prevention of Cavitation or choking

 

[LittleInch]

peter vaf.

bcd called it correct in the first post, but you don't seem to have understood?

That chart you put up is a bit of nonsense. What it is trying to show is what happens when you use any of those types of valves as pressure reduction / regulating , i.e. with a constant dP. Now assuming that the graph is proportional, the fixed DP is some 40% of the inlet pressure. Hence for a ball valve it will be probably about 95% closed.

All that it shows is that, surprise surprise, the valve which is actually DESIGNED to regulate pressure - the globe valve - is actually quite good at it and the others are not so good.

If you only want to isolate, use a ball, gate, butterfly or plug valve. If you want to control pressure or flow, use a globe valve. If your pressure drop is low as a percent of inlet pressure, a butterfly valve can be OK as well.

What do you want this valve to do??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bcd]

If you want to compare valve flow performance at full open, compare the Cv. This will tell you how much flow of water will pass through the valve with a 1 psi pressure drop. You will see that the amount of flow through a ball valve is many times greater higher than through a globe valve.

 

[LittleInch]

Remember that a high CV means more liquid will flow in one minute for a 1 psi pressure difference, So the higher the better if you want low pressure drop when fully open

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

But a segmented ball valve must be chosen for a reason? I think they are easier i GMP installations since there are fewer nooks and crevasses that cannot be CIP'ed? Be causefull here! And your graph is for a "generic ball valve" and certain special ball valves may have improved control characteristics.

--- Best regards, Morten Andersen