Author Topic: Question about restriction introduced by CSV, sanity check on my calculations  (Read 209 times)

Kurt_L

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Hi, I am setting up a brand new well to supply house water at my farm in Oregon. The well is 57 feet deep, with water level at 31 feet.  I presume that I will install the pump a couple feet off the bottom of the well, say 54 feet.  The well log says that the driller did a 1 hour test that yielded 40 gpm with pump depth at 56 feet.

After watching the chaos in Texas a week or two ago with power outages I've decided that one non-negotiable for this pump is 115V operation.  I know that limits my flow, but I'm willing to forgo simultaneous showers in order to be able to run the well pump off a solar electric system that is already in service.  The old well was supplying water through ancient galvanized piping that was restricting flow, so we're kind of used to low flows - we're probably getting 3 gpm max at the downstairs bathtub now.

The pump that I've tentatively identified as a candidate is the Grundfos 10SQ05-160.  It seems reasonably sized to the application, runs off 115V, and has a soft start feature that is important so as to not overload the solar inverter.  One of my questions is how does installing a cycle stop valve affect my design calculations; here I'll run through the calcs as though the CSV is not present, and then perhaps Cary would comment on whether the CSV will affect things so much that I need to alter the design?

If assume that the pressure switch is 40 psi on / 60 psi off, then the equivalent head heights for those two pressures are (pressure * 2.31), so the pressure heads are 92 feet and 139 feet.  Adding in the pump depth of 54 feet then the approximate total head is 146 feet at turn on, 193 feet at turn off.  Checking this against the pump curve, it looks like the two flow rates are 11.1 gpm at turn-on and 7.2 gpm at turn-off (see attached pump curve).

I went to the calculator page, and plugged in 11 gpm, 50 psi desired pressure, and 72 psi as the max pressure at CSV inlet (I got the latter by noting that the pump max head is 220, subtract off well depth of 54 feet, convert 166 feet to psi by dividing by 2.31, resulting in 71.8 max psi at top of well). When I ran the calculator with the 60 psi pump cut-off pressure the calculator said no valve applicable - not sure why?  The calculator suggested either the CSV12550-1 or CSV1A; I was thinking I would just order the PSIde-kick kit, so is there any reason to consider the CSV12550-1?

I'm not sure how to phrase the question properly, but I'm assuming that the CSV introduces some loss at maximum flow conditions - is there a way to predict how much the flow will be reduced when operating at the point where pressure on output is just about to drop below 50 psi?

Some other sanity checks here:

I'm going to put the tank and CSV in a garage that is adjacent to the well head, so I can use hard pipe from drop pipe to CSV to tank.  I'm assuming that PEX pipe would be the commonly used tubing from tank through the ground to the house cellar.  Based on this resource http://s3.supplyhouse.com/manuals/1322593642270/68976_PROD_FILE.pdf, it looks like 1.25" PEX is the appropriate size for the 50 foot run to the cellar.

Based on this resource for pressure loss in PEX tubing (second page of https://mrpexsystems.com/wp-content/uploads/2016/08/17-Pressure-Drop-Charts.pdf, it looks like the loss is 1 psi at min flow, 2 psi at max flow.  This seems acceptable.

I read in some other posts that in some cases one can use threaded PVC down pipe; with the max 220 feet of head the pressure should be 95 psi max, correct?

Any red flags in what I've proposed here?  Thank you for your time and wisdom.

Kurt
Albany, Oregon

Cary Austin

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Well if you were watching the chaos in Texas you should know that solar is not a good backup supply.  We were cloudy for days and the only reliable source of power was gas powered generators.  With a generator 230V is not a problem, and works better for pumps.  However, the pump you picked would work, but I would use the 10SQ05-200, so as not to be right on the razors edge of working at that depth.

Pex pipe is fine, just use one size larger than normal or the friction loss from the insert fittings will be more than you want.

A CSV only restricts the pump when needed.  There is a few pounds of friction loss in a CSV. But the only time you would see it is when running the pump at max flow, which is rare.