Calculate Max Flow through failed PCV 2

[ChEMatt]

I'm sizing a PSV for a failed regulator case. We have a 600# class system upstream of the PCV, and a 300# class downstream. The fluid is hydrogen, and we've determined that the max upstream pressure is 1350 psig, and the not-to-exceed pressure downstream is 450 psig.

This is a 1/2" tubing line and the regulator is a small Jordan JPR regulator. The product data sheet gives C_v for the valve, but no C_g. I've been looking through my Crane, Fisher Catalog 12, and GPSA manuals trying to find the right equation, but I keep running into roadblocks.

For compressible fluids, Fisher gives an equation that is close to what I need, except that I need a value for X_T. This value corresponds to the type of valve, and no such value is given for the Jordan JPR PCV. If I had X_T, I could finish the equation. Is there a rule of thumb for values of X_T?

Likewise, Fisher gives an question C_g = C_v/C1, however C1 is explained: "C1 of the valve under consideration". Another value dependent on the type of valve, which is not given by the Jordan data sheet.

A third equation that I was given by an associate is q = P1*C_g, where P1 is in absolute units (psia). I do not know where this equation comes from, and I do not know the units of q (scfm, scfh, gpm??) Can anyone tell me where this equation comesm from?

It appears that I need to get either a C1, C_g, or X_T value out of the valve manufacturer. Is there another way to calculate what the max flow through this PCV? Is there a rule of thumb for X_T or other values? If I cannot get C1, C_g, or X_T is there another method that will give a usable value for flowrate through the a failed/fully-open Jordan PCV?


I appreciate your help. Thanks!!

Onwards,

Matt

 

[pleckner]

Is there a reason you don't want to talk to the vendor?

 

[Latexman]

If the tubing and PCV are both 1/2" (you didn't mention a bush or reducer) you probably have a JHR, not a JPR. Check it out.

With the ID of the tubing and Cv of the PCV, you have all you need to get a K for the PCV. In Crane, Equation 3-16 can be rearranged to K = 891d⁴/(Cv)².

Then, combine the K's of the entire system and use your preferred version of Equation 3-20 like in Examples 4-13 and 4-14 to calculate the flow rate for your scenario.

Good luck,
Latexman

 

[CMA010]

Download the Masoneilan Control Valve Sizing Handbook.

Assuming choked flow you can use:

W = (Cv*Cf*P1*SQRT(Gf))/(54.4*SQRT(z))

W, mass flow rate [t/h]
Cv, Valve flow coefficient
Cf, Critical flow factor (use 1)
P1, Upstream pressure [bara]
Gf, Specific gravity at flowing temperature
z, Compressibility

 

[ChEMatt]

pleckner: the vendor is difficult to nail down, i.e. left messages but didn't hear anything back for two days.

Latexman, my guy confirmed that there is a reducer before the PCV which reduces down to 1/4". I will research your answer. Thank you!!

While I have your attention, I was sent the source of the third equation I mentioned above. Q =P1*Cg, where Q is in SCFH. Does this equation pertain only to the Fisher 95, or does it apply to all pressure regulators/control valves? I've searched but been unable to find a resource to support this equation beyond the 95 Series. Any thoughts?

Onwards,

Matt

 

[BenThayer]

i like latexman's response because he is saying look at the system, including piping/tubing, etc.

our relief device "experts" like to look only at the PCV and apparently think it has a 6" supply line and an 8" outlet based on the max flows they predict!

 

[JoeWong88]

Calculating Max Flow through failed OPEN CV...

- Hope you have considered maximum upstream pressure (PAH or PAHH)

- Credit may be taken for small ID piping/tubing as recommended by Latexman

- As flow passing a CV is dependent on valve design and construction, thus some vendor may have dedicated set of equations and parameters used in estimating maximum load. Using vendor A set of equations for valve manufacture by vendor B may not be suitable...

- Using common methods e.g. ISA, K factors, etc would only be recommended during preliminary design phase. However, it shall always confirm with the selected valve from a manufacturer by using dedicated equations. On the hand, conservative rate estimated using common method can always be taken.

JoeWong

 

[ChEMatt]

Joe,

Yep, that's pretty much what I thought. In the past, in the absence of information I used Crane to conservatively estimate the flows. I am still in communication with the manufacturer and I hope they will soon provide me with the data I need. It will be a very small PSV, but we need it nontheless to protect the system.

Thanks to all for your responses.

Onwards,

Matt