CSV recommendation for ~55GPM zones and 2" piping

[enorl76]

So first off I have installed several zones on a large acreage yard that run about 50-55 GPM.  I have a Sta-rite D-series 3HP pump, currently just running manual on/off via circuit breaker.  There's 2" hunter PGV valves but manually operated at the moment.  The zones are working nice, but there's more to do.

The 50GPM CSV model seems just out of reach for that scenario, but I'm concerned about the price of the 2" versions, where the price is just about more than I'd really like to spend.  So let's entertain the idea of the 1.25" version for a moment.

I was also thinking though, doesn't reducing the size of the pipe from 2" to 1.25" cause a high velocity flow problem through the CSV?  WHen I look at water velocity tables from http://www.engineeringtoolbox.com/pvc-pipes-friction-loss-d_802.html , for 2" PVC sch40 pipe, its about 4.9 ft/sec.  When you go over to 1.25" pipe, that jumps to 11.1 ft/sec and a head loss of 30 ft/100ft and friction loss of 13.2psi/100ft...

Now I can slightly modify the system to drop down a bit in GPM per zone by adding a new zone in the middle of the backyard and redistributing the heads a little. But my original thought remains where I question putting a 1.25" device on 2" pipe.

Is my concern unwarranted?

And second, I wonder if redistributing the zones to have less GPM would be better?

[Cary Austin]

Losing 30’ of head for every 100’ of pipe doesn’t add up to much when the 1 ¼” valve is only 6” long.  It is very common for the CSV to be a size smaller than the pipeline, because the CSV is sized to the pump, not the pipe.

The 2” CSV3B2T cost $647.50, but is the Cadillac of valves.  It is heavy duty, long lasting, adjustable, low head loss, NSF approved, etc..  However, a CSV1.25/40 will have the same performance up to 50 GPM and sells for only $111.00.  You just have to be careful not to install the plastic valve in a bind.  They do not handle sand or debris as well and are not adjustable like the 2” valves.