Flow Coefficient of cage trim 1

[Pegasus2]

Could anyone explain how to determine the flow coefficient of the following linear cage.

For a 1" globe valve
Cage attributes, hole diameter=.312ø, total holes=24
1-5/16" Port, 3/4" Travel

I need to calculate the Cv @ 100% Travel?

 

[TD2K]

Is this a trim that you've made because typically, the vendor has this information.

I suppose as a first pass I would look at how much water I would pass through a 0.312" orifice with a dP of 1 psi. Multiply the number of gpm through one orifice by 24. Since the Cv is the number of gallons of water a valve with pass with a differential of 1 psi, the total number of gallons you calculate through the 24 orifices = approximately the Cv.

That ignores totally the flow characteriscs of the valve itself I realize but I'm not sure how to factor that in. If the Cv you calculate is significantly less than the Cv of a conventional globe valve you should be in good shape ignoring the dP losses through the rest of the valve other than the orifices in the trim.

 

[MikeHalloran]

The Cv of 24 x 5/16" diameter holes is approximately
42.68 gpm/sqrt(psi)
Which is also the Cv of one hole of
1.531" diameter
That assumes sharp- edged orifices; no burr, no chamfer, no radius.



Oh. You want to know how to do it;

Start with hl = V^2/(2*G)

Where the V is based on an effective orifice area, in this case 0.61 times the nominal orifice area.

Compute hl for an arbitrary flow, convert hl from feet wc to psi, and compute Cv = flow / sqrt (psi)



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[JimCasey]

The area of the 24 holes is greater than the area of the seatring orifice. Therefore the seat will be the limiting factor. Your Cv will be around 29. Also, your characteristic will be "quick opening" since it will be linear up to the point where the seatring becomes the limiting orifice, then additional travel of the plug will not reward you with correspondingly higher flow.

Typical Globe control valves have Cv in the 12-15 range for "full area" trim. You may find that you have more Cv than you can use, and your valve will be throttling over a narrow band near the seat.

 

[stanier]

Valve Cvs are normally determined by testing. Contact the valve manufacturer.

 

[Scotsinst]

Fisher 1" ED (or ET) has 3/4" travel and 1 5/16" port diameter so your valve is likely a Fisher valve or copycat.
I don't recognise the hole description of the cage (sounds like a Fisher HP type cage) but your Cv is likely to be maximum 22.1 (QO cage).