Check valve head loss 1

[dianad]

Hi,

Can anyone confirm this to me please.
Does a check valve has a different had loss value, if it's installed in a vertical or horizontal pipe?

Thanks

 

[MJCronin]

diane...

It depends on the style of the check valve.

There are check valves that will not operate in a vertical or horizontal position ("flapper check and ball check).

What is "a different had loss value"...???

-MJC

 

[dianad]

Hi,

I mean head loss (pressure loss) in the check valve.
I ask this, because my idea is that if we have a check valve vertically, it has an upper resistance due to the water weight, that hasn't when is installed horizontally.
Am i correct?

 

[BigInch]

That's something else. It is static head, not frictional flow head. Valves, pipes, other flow elements have frictional losses. Elevation change doesn't, it has "elevation losses".

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[dianad]

So, how can i calculate the pressure loss in a check valve installed vertically?

 

[btrueblood]

by using the hydrostatic "law"

P = rho*g*h

rho is mass density, g is accel. due to gravity, and h is the vertical height difference. P then is the pressure differential between two points seperated by vertical distance h.

 

[BigInch]

Get the flow coefficient "Cv" of the check valve.
Flow_GPM / Cv_GPM/psi^(1/2) = (diff_Press_psi)^(1/2)



"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[btrueblood]

Ok, realistically, a sum of my equation and BigInch's.

 

[BigInch]

same same, but a more common valve attribute that many valve mfgrs give in their data tables.

Caution units of Cv may vary.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[dianad]

Thanks for the replies.

I'm a bit confused about the answers. Normally i use the formula that i use with any local loss, wich includes that Cv factor that BingInch mentioned.
My doubt, and that was yet clarified, is related to this factor. Does it change if we consider vertical or horizontal pipe? (knowing that the rest of the formula stays the same: velocity,etc)

Thanks

 

[BigInch]

No, as for any valve, Cv doesn't change with orientation. What does change is the pressure drop across the valve. That changes slightly with orientation, if installed with an angle to the horizontal, due to the density of the fluid x elevation difference between inlet and outlet that will result.

So use the formula above for frictional head or pressure loss, being sure that your known inlet or outlet pressure includes that due to elevation considerations, as it should, then the total pressure drop across the valve will be the sum of that calculated by Cv formula plus or minus the fluid density x valve length x sin(alpha), where alpha = angle that the valve makes with the horizontal plane.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[dianad]

Thanks BigInch,

Now i understood perfectly what you said!
One last thing: isn't this elevation loss consideration included in the total height elevation between the lower and upper point of the pipe, used to calculate also the pump head needed?

Thanks once more

 

[BigInch]

Yes. If you do the typical kind of pipe flow calculation, pressures due to elevation changes will be included.

Generally you can assume the valve is a point, without any length and calculate the pressure due to elevation change and frictional loss up to that point, then apply the Cv friction loss equation to get the pressure drop across the valve, and lastly, calculate the unknown pressure on the other side of the valve.

I can imagine some special type of flow element where the point assumption might not be true, a very very long valve for example, but that's stretching it pretty far outside the customary problem.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[engrsh]

How to check the pipe sizes of Natural Gas line are correct or not (correct capacity, pressure required and pressure drop ect.), any design criteria ?

 

[BigInch]

engrsh,

Please start a new thread.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[btrueblood]

Back to the check valve...BigInch is correct (Cv of check valve is independent of orientation) except in a very narrow, specific range of flow conditions:

If the check valve poppet is big and heavy, as it might be for a very large valve, then the weight of the poppet may change the restoring force, and affect the Cv of the valve slightly, at pressure drops near the cracking pressure of the valve. I.e. until the poppet has moved from its seated position to its full-open position, the Cv of the opening is dictated by the balance of spring, gravity, and fluid dynamic (e.g. drag) forces.

 

[BigInch]

Hopefully he can find a Cv curve from 0-100% open, but not many check valve manufacturers publish those. Most of the time, you'll only get a Cv at full open, if they even have that. Lots of mfgrs don't publish anything at all in the way of Cv for checks.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[BigInch]

Huh. Found a dP/Q chart I had laying around.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com