Equivalent Lengths for Ball Valves

[dieselelectric]

I've always used the "Cameron Hydraulic Data" book for pipe friction loss calculations. I like the equivalent length method because it's simple. However, I can't find an equivalent length for a standard ball valve. Anybody know where to find it?

 

[CRG]

Depends what you mean by a standard ball valve, reduced port? You can get the Cv from the manufacturer and calculate the equivalent length.

 

[zabrab]

Multiply the equivalent length of a gate valve by K(ball valve)/K(gate valve).

References to 17th edition, 1st printing

L=KD/f (pg 3-110)

D and f would be constants for both conditions, gate valve and Ball valve. Only variable is K.

Use "Friction loss of water in pipe fittings in terms of equivalent length (L) feet of pipe" (pg 3-120) for eq len of gate valve.

Use "Friction Loss in Pipe fittings" on pg 3-111 (chart of K values) for the K values for gate valve and ball valve.

Example: Determine eq length of gate valve based on 90-deg bend, 6" diamter pipe (these fittings are in both tables)

K(gate valve)/K(bend) = 0.12/0.45 = 0.267

Eq Len(90 bend) = 15.2 ft; Calc'd Eq Len (gate valve) = 15.2*0.267 = 4.06 ft

From pg 3-120:
Eq Len (gate valve) = 4.04 ft

 

[stanier]

Why not download Epanet and use the Darcy Wiesbach apporach. This is free software and is simple to use and will provide more accurate results.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au

 

[katmar]

The values I have for the equivalent lengths of ball valves are 4.0 for full bore valves and 22.0 for reduced bore.

Of course these are generic numbers and the actual values will vary from manufacturer to manufacturer, especially for the reduced bore valves. For mission critical calcs follow CRG's advice and get actual Cv values from the manufacturers. However, process engineers are often required to do pressure drop calculations long before orders have been placed and at that stage we do not know which brand of valve will be selected.

An often overlooked advantage of using L/D values rather than K values for valves and fittings is that the L/D values vary much less with Reynolds number and size than do the K values. For example, at a Reynolds number of 2 (extreme laminar flow) the L/D value for the full bore valve would increase by 25% to about 5.0. If you were working with K values you would find the value had increased by a factor of over 1000. Unfortunately, many popular references (including Crane 410) do not make this clear.



Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[vzeos]

dieselelectric:

Take a look at Friction Loss in Pipe Fittings on page 3-111 in Cameron. Find the table entry for Ball Valves. Just to the right of the ball valve picture is the number 3. This is the L/D ratio, where L is the equivqlent length and D is diameter. This means that if your diameter is 12" then your equivqlent length is 36" or 3 feet.