Determining Control Valve Cv

[nctexan22]

I am designing a 1", quarter-turn ball control valve and in need of some overall guidance.

The inlet and outlet seat trims are modified with a pattern of holes intended to help reduce flow. The valve is required to pass water at a flow rate of 19 gpm, with inlet pressures ranging from 750 psig to 350 psig, while maintaining an outlet pressure of at least 150 psig.

Plugging this data into Cv = q (SG / dp)1/2, tells me that my valve must have a Cv ranging from .77 to 1.34.

My unknown is obviously pressure drop, as unless a prototype is produced and tested, the resultant p.out from the inlet pressure range is unknown.

How do I go about determining what the pressure drop will be at differing degrees of valve travel without a flow test/ CFD software?

I have been studying ANSI/ISA-75.01.01 and it seems as if these equations are geared towards globe and butterfly valves.

Any help would be greatly appreciated.

 

[PaoloPemi]

I am not an expert in this area but I see you haven't received answers so I add a note, if I understand your design (which I do not comment) where pressure drop is produced mainly when fluid pass through calibrated holes I would start estimating the individual flow (and cv) on each hole (for example considering a hole as a micropipe or a orifice) then the total flow (or cv) would be the sum of flows in working holes.

 

[BigInch]

I'd start by looking at other manufacturer's valves position vs Cv curves, then figure out what's going to be different about yours ... if anything. Should be pretty close.

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"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)

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[nctexan22]

PaoloPemi, you are understanding the design well, given the amount of detail I've provided and I appreciate your input. Allow me to elaborate:

The inlet of the valve is 1" in diameter. The seat trim pieces have a pattern of various diameter holes, so when the valve is cycled and the ball is turned to a certain position, only certain diameter holes are exposed to flow.

If a flow rate of 19 gpm is fed into the 1" inlet bore, that flow rate will remain constant as it enters and exits the smaller holes in the seat trim, granted the upstream pressure is enough to maintain it, correct?

The velocity of the fluid as it goes through those holes will have to increase, however, from what it is traveling at through the 1" bore. The problem I am faced with deals with a velocity limitation for the material of the seat trim (titanium). Velocity must remain under 120 ft/s.

My current big question is this: If multiple holes of small diameter are exposed to a flow rate of 19 gpm, will the flow velocity through these holes all be equal to that of if only one hole were seeing the flow rate, or will the velocity be less overall through each hole?

 

[BigInch]

OK, that's a better explanation.
No, its different. I have seen a number of studies of multiple orifice plate fittings (in series) published by manufacturers of those devices that suggest significant variation in multiples rather than what you would get with just one. Search for Multiple orifice fittings and you may find one of those studies. (If I do understand your configuration correctly.)

**********************
"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/