K factors for Hydraulic Manifold Block

[djw2k3]

Hi all,

Does anyone have any suggestions or know of published data on K factors for a machined hydraulic manifold block. What I am most interested in is a typical 90 degree bend (eg R/d = 0) created from boring into the block from different sides of block.

Also, does standard 'equivalent length' theory hold if the bends are only 2 or 3 diamters apatr?

Dave

 

[BigInch]

There is more than one K factor for a valve. K factor varies with valve position or percent open.

Using a series of standard Ks for any custom machined valve wouldn't be very accurate. It would be much better to test the valve and determine the exact K factors from the closed position all the way to full open.

Possibly you may find some simularity to Ks for an angle globe valve, but I doubt it.

Theoretically you can add Le without regard for distance between fittings, but there is bound to be some unquantified effects. Those Le values could not be developed for every piping configuration. Although though you can get 12 significant figures from a hydraulic analysis spreadsheet, don't count on getting real accuracies within more than 2 significant figures. Be conservative and allow yourself from +/- 10% up to 20%, depending on the configuration.

http://virtualpipeline.spaces.msn.com

 

[vzeos]

djw2k3,
Your description suggests you can use the K factor for a 90 Deg miter (one cut).

There is a proximity interaction that is normally ignored in process piping. There are some correction factor tables and charts published for bend-bend interactions in Internal Flow Systems Design and Performance Prediction by D. S. Miller.

 

[djw2k3]

vzeos,

Unfortunately I don't have access to this particular book, but you are correct a 90 deg mitre is the closest description I have seen. The only reference to a loss factor k for this I can find is 1.1 from BS Massey.

 

[katmar]

djw2k3, you have not given the diameters of the holes you are drilling into the block, but I would guess that they are smaller than typical process piping. The data given by Hooper and by Darby suggest that the K values for single weld 90 degree miters increase as the diameter gets smaller. I doubt that anyone has made up miters as small as 10 mm and tested them, but the data suggest that at this size the K value could get close to 2. Unless you are very close to your pressure drop limit this is probably not going to make any real difference and using Massey's data is OK.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[djw2k3]

Hi Katmar,

Yes the diameters are around 20mm - 30mm. Thanks for the input.

Dave

 

[Mech85]

djw2k3

The Cameron Hydraulic Data handbook gives the following resistance coefficient K values for 90 deg mitre bends versus pipe size : -

Nominal Pipe Size K Value
1/2" 1.62
3/4" 1.50
1" 1.38
1 1/2" 1.26

Hope this helps.