To empty a tank on occasion, I'm planning to install a PD pump, pumping about 30-60 gpm of warm water through a 2" line. At the end of the line my circuit will join into a larger 50 psig line. I'll add a check valve for when my line's not in use. Right now I'm doing the hydraulics and selecting the pump.

The problem is, I will probably have to tie my 2" line into the 50 psig line via an existing 3/4" diaphragm valve. I've got no model number/data for this valve, so thought I would just get out Crane 410 and estimate the pressure drop with K-factors. Except there is no K-factor for diaphragm valves in Crane, nor anywhere else I've looked.

Does anyone have a K-factor for diaphragm valves, or any other suggestion to estimate it? Should I just get three vendor catalogs and take the highest pressure drop from them? The valve is SS, SCH80 and probably a Teflon diaphragm.

For comparison, at 60 GPM a 3/4" globe valve is >60 psi loss, whereas a gate is ~2 psi. So it's not insignificant how I do this.

For a 3/4" weir type diaphragm valve I use a K of 4.5.  If you have a teflon diaphragm it is likely to be a weir type valve because teflon does not have the flexible of the other elastomers. Forgive me for stating the obvious, but remember to apply this K to the velocity in the 3/4" line and not that in the 2" line.

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