Ball valve flow rate & pressure drop 1

[thought2007]

In ball valve is Bernoulli principle used to estimate the values flow rate & pressure drop estimation
And what will be the difference with ventury flow path & Straight flow path

 

[katmar]

Flowrate and pressure drop in valves are calculated using the "Valve Coefficient", usually written as C_V. Googling will give you umpteen references - see for example

http://www.pdcvalve.com/sizing/sizing2.html#liquids

The better suppliers' catalogs give C_V values for their valves. C_V varies with valve type and size.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[JimCasey]

Straight flow path (Full bore) has the same pressure loss as an equivalent length of straight pipe. Maybe less, as the ball has a better internal surface finish than pipe.

It is more customary for a ball valve to have a "standard" port, which is typically one size reduced. There is a theoretically larger loss. In practice, the loss is about the same as one experiences fron an elbow.

FULL bore is really only required if something solid, such as a pig or an instrument probe, has to go through the ball.

 

[gerhardl]

Hello Jim,

as usually good and to the point, but considering all variations of applications and types, not necssarily true for all.

If you have a look at the specialized application turbine inlet valves for hydroelectrical power plants (mecanically pure water) you will find following combination of requirements:

a) Fastest practically water speed adapted for the water distribution drum before the turbine. b) Least possible loss.

Result-> often selected double eccentric ball valves, full bore, with flow also round the ball in addition to full flow through the full opening.

Also for smaller ball valves for general/other application I believe (my personal view, no statistic) the trend in Europe to lean a bit more towards the use of full-bore in stead of reduced bore ball valves than in the US.

 

[BigInch]

The logic behind it is a full port doesn't cost you money to operate.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JLSeagull]

Some threads on this site suggests little price difference between standard reduced ball valves and full bore valves. I think that someone actually indicated that full bore valves cost less.

 

[bcd]

The larger the valve, the greater the weight and cost difference between full and standard bore. Full port means larger diameter ball, means larger body, means more torque to operate, means larger, more expensive operator, etc. Also more expensive to maintain.

I'll agree that in very small sizes (like 1 inch), it's not that big a deal. But in 12 inch valves, it is.

All things being equal, full port is more expensive to purchase, and the resulting flow loss of using standard ball is normally negligible considering other losses in the system. In such cases, you won't regain the difference in purchase price in energy savings.

bcd

 

[BigInch]

bcd,

Just figuring a handwheel operated valve, using typical Cv for ball valves, a power cost of 0.8 ¢/kWh, more or less reasonable costs for valves (who knows what those are today), a 5% interest rate and what amounted to a 20% cost difference for 12" full vs reduced port, it seems extremely likely that, even if you vary those numbers quite a bit, full ports would pay for themselves at some point during the life of a typical facility. (See attached.)



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[bcd]

Just checked our price list. You are either getting a really good price for full port, or are getting ripped off for reduced port. For a 10" carbon steel with stainless trim, full port is over 200% more expensive than reduced port. This does not include the cost difference for the operator. Just the valve. A million cents pays for a lot of kWh.

 

[BigInch]

I don't have a current price list.

What's the prices for the other sizes?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

Post your price list (no names), your kWh cost and I'll revise it and post the xls for you.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JimCasey]

Occasionally I will have a customer ask us to run a calculation to prove that the pressure loss through a valve does not exceed some value. 10 psi is frequently mentioned.
Almost invariably when I calculate for a regular port ball valve, the pressure loss is o.oo3 psi or in that range.

Sure: a full port valve may have 10% as much loss, but when the regular port valve's loss is too low to measure in the first place is is GOING to take a WHILE for any economic benefit to be realized by using a full-port valve..

 

[BigInch]

Jim, 0.003 is only a liquid velocity of 0.25 fps in a 3" valve. Are you talking gas pressure drop?

Granted payback does, at the very least, take a "while".

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JimCasey]

I spoke from memory on the 0.003 psi drop. I remember it as being too small to measure without "laboratory" equipment. Sorry if I exaggerated.

Actually running numbers:
I selected a McCanna ball valve as representative.
3" standard port has a Cv of 397.
230 GPM gives a velocity of 10fps in a 3" SCH40 pipe.
the valve would have a DP of 0.59 psi in that installation.

Substituting an otherwise identical McCanna full port valve:
The Cv for a full-port 3" valve is is 763.
The DP is 0.16 psi at the same flow.

so the DP is 0.43 psi less with a full port valve in this application.

It's meaningful as long as there is not a control valve in the system running slightly more closed, absorbing the same energy that was liberated by opening the ball valve port a bit.

Meanwhile: the full-port valve costs a lot more, and the actuator torque goes up by some greater-than-1 exponent.

My point is: Most of the time a full-port valve is unjustified. Probably 95% or more. SOMETIMES, it matters. Digester Blow, Peelers, Pigged pipelines, Instrument tap valves, to name a few apps.