Ball Valve Sizing2 1

[joisy]

Hello,

can someone explain me if I'm able to find the internal dimensions of reduced ball valve, knowing that it's made in comply with API 4D and has Class 600. I've looked at that API (have for 1996), but nothing was stated about the relations between ball bore size and valve nominal diameter.

thanks in advance

 

[atad]

The best way to tackle this is to talk to the valve vendor that you propose using.

 

[briand2]

Joisy,

I think you'll find the API and Class 600 references relate to the valves ability to withstand temperature and pressure. This is why they have nothing to say on the valve's internal dimensions.

You would be better off looking at some manufacturer's literature or websites, as the actual dimensions of the hole through the ball vary from valve to valve.

Regards,

Brian

 

[DLANDISSR]

Joisy:
Have you considered using a full port valve if a reduced port valve is a problem?

 

[tsenthil]

API 6D and ANSI 600# class nothing to do with internal dimensions of a ball valve. Please refer Ball valve manufacturers catalogue for dimension details.

 

[mridey]

Joisy:

You might take a look at API STD 608, which covers ball valves and defines the dimensions required for full, regular, and reduced port valves.

The bad news is that not all ball valve manufacturers comply with API 608, so you may be left with checking catalog data anyway.

 

[saxon]

joisy (ya ain't from thoitythoid and thoid in Poith Amboi are ya?), Why the concern about full and reduced port sizes in ball valves? Just remember, for liquid sizing:

Q=cv*(dP/g)^1/2 Q=flow gpm
cv=valve coefficient
dP=diff. press. psi
g=sp. gravity of fluid

for gases use the gas sizing form.

Simply calculate the required cv and pick a ball valve that matches or is greater than.

Don't worry about wether its reduced port, full port or in between port.

Hope this helps.
saxon

 

[joisy]

Saxon,

can you please advise the formula for gas flow as well

thanks,
joisy

 

[saxon]

joisy, Ok, are you ready for this? The following is the Universal Gas sizing Formula:

Q=cg*P1*(520/G*T)^1/2*sin((3417/c1)*(dP/P1)^1/2)

Where:
Q=gas flow, std. ft^3/hr.
cg=gas sizing coeff.
c1=cg/cv
cv=liquid sizing coeff.
P1=inlet press., psia
dP= pressure drop across valve, psia
G= gas specific gravity
T= gas absolute temp., deg. R

NOTE: (3417/c1)*(dP/P1)^1/2 must be equal to or less than 90. If greater than 90 the form will indicate reducing flow, which is impossible.

Now that I have thourghly confused the issue, have fun.

saxon

 

[TD2K]

Just to confuse the issue some more, Saxon's formula is really valid only for ideal gases where Z = 1.0.

It's Fisher's equation for valve sizing out of their catalogue and they have another formula for any gas at any pressure and temperature (eg. where the compressibility is not equal to 1.0).

However, you can make the equation valid for any gas at any pressure and temperature with one slight modification:

Q=cg*P1*(520/Z*G*T)^1/2*sin((3417/c1)*(dP/P1)^1/2)

Where Z is the compressibility factor.

 

[saxon]

TD2K, Ah yes! the real worlding "ZED Function". I knew I was forgetting something. Anyway, it will get them close enough.

saxon

 

[joisy]

I've found this formula in Fisher Valve Catalogue, but the problem is that valve is intended to handle liquid - not gas and no Cg coeficients is set for it.
Your question maybe why I do calculate this for gas if it's not intended for? Because I need to calculate some abnormal plant operation when in place of the liquid the line handles gas. Nothing got from Emerson (Fisher) on this issue

 

[TD2K]

Look up the cut sheet for the valve in the Fisher catalogue for the model of valve you have (eg, 3" class 600, EHD, linear trim). They list the Cg, Cv and Cs (steam sizing coefficient) for the various sizes. If this valve is a globe valve, commonly (but not always), Cv is about Cg/30.

 

[joisy]

Faugh! I did find valve's data, but not in Fisher catalogue and via Fisher Firstvue software (recommend everyone who deals with Fisher valves,

http://www.emersonprocess.com/fisher/products/softwaredown.html).

by the way: last equation can be re-written as:

Q=1.06x((RoxP1)^1/2)xCg x SIN(3417/C1 x ((dP/P1)^1/2)), lb/hr; where Ro is gas density (pounds/cub.feet)

I've got some advise that max flow through this valve can be calculated as chocked flow (Vs-sonic volume) by formula:

Vs=(KRT)^1/2, where K is specific heat ratio (usual 1.3), R=R0/M. Q=VsxSxP/(ZxR0xT). S:=Dp^2x3.14/4, where Dp is the port size.
It doesn't seem to me to be the right way, and what you think of that?

 

[TD2K]

Actually Saxon, you didn't forget the Z function, Fisher doesn't have it in the equation you posted. You need to do some digging but that equation is intended for an ideal gas. For a non-ideal gas, you have to use the 'any gas at any temperature and pressure', the equation Joisy posted on April 28th.

However, you can do some manipulating of the equations and show that the two equations become identical with the addition of the Z term I suggested.

Joisy, the maximum flow through your valve is at choked flow or when the sin{ } term equals 1. Then, you have:

Qmax=1.06x((RoxP1)^1/2)xCg OR

Qmax=cg*P1*(520/Z*G*T)^1/2

Watch your units. Q in the 'ideal' gas equation is scfh. In Fisher's 'any gas at any temperature and pressure equation', it's shown as Qs in their catalogue with units of lb/hr.