jamesgangnc wrote in news:e2726069-c968-4f1a-
:

Thanks for the pointers on the last one. Much appreciated. I had no
idea there were suction limits. I have not talked to the corp yet but
I have heard via others that they do issue permits for personal
irrigation usage. And from the response to my last post I'm thinking
the only practical solution for me is a shallow well jet pump. The
pump can remain on my property and I can easily supply electrical
power. Running power to the lake is out of the question because o
fthe flood issues. The corp is very restrictive about that. I just
have to run water lines down to the jet foot in the lake. That's the
part I'm investigating now.

I'd like something cheap and easily taken up or moved if needed. I
see that normally some pretty large pipe is used for a home jet pump.
And it's not cheap. But I also only need to accomplish 30 psi at
about 2 gpm. I'm wondering if I can get away with 1 inch poly for the
main pipe and 1/2 inch poly for the jet supply? Any thoughts? Again
the lake is about 250' away with a 25 to 30' rise to the house.
Thanks to all :-)

Are you sure of the 2 gpm rate? Seems a bit low to me but if all you need
is 2 gpm then you could use 3/4" for the main pipe and 1/2 inch for the
jet supply. Smaller pipe is easier to prime so don't over-size it. Get a
good foot valve to make priming as easy as possible and hopefully one
priming will last a long time. Priming and keeping prime is the main
disadvantage of long pipe runs from the source.

For your 2 gpm you need a pump that will supply 2 gpm at 102 feet of
head - 3 ft friction losses, 69 ft for the 30 psi pressure and 30 ft for
the static lift. The equation for horsepower is hp = (gpm x head in
feet)/ (3960 x efficiency) where efficiency for these pumps can be as low
as 60% (0.60). That is only 0.09 hp for your 2 gpm need. You can use the
smallest pump you can find that will make 102 ft of head at 2 gpm and
that may be hard to find as small pumps usually don't make that much
head.

I did the calculation for 5 gpm and get 22 feet of friction loss in a 3/4
inch pipe. That means a hp of (5gpm x 121 ft)/(3960 x 0.6) = 0.255 hp. So
a 1/4 hp pump would supply a lot more than you need and that size is easy
to find but again the head rating is important.

There is no problem with an over-size pump, in this case. The pump only
draws as much power as it needs for the amount of water being pumped so
even a 1/2 hp pump wouldn't waste much electricity. Running a pump lower
than it's best range makes it operate in a less efficient range but that
might be 50% instead of 60%. It wouldn't harm the pump physically because
2 gpm is enough to lube and cool. So, if you can only find the pressure
requirement in a 1/2 hp pump and the price is right that is OK. Check the
shut-off head (head at zero flow) to make sure that your pipe can handle
that pressure. In the 1/2 hp range there are many pumps that make a lot
of pressure so be careful of that.

Also, use a pressure tank and probably a 30/50 switch - starts pump when
pressure falls below 30 psi and stops pump when pressure reaches 50 psi.
You divide psi by 0.433 to get feet of head. The pump's shut-off head
must be higher than the higher number of the switch or it won't make
enough pressure to cause the switch to turn off. These switches are
usually adjustable with a screwdriver so you can likely get a setting
that will work with your pump - just turn all the taps off so flow is
zero and if pump turns off at 50 psi, great. If it keeps running adjust
the shut-off screw until pump stops and then turn screw a bit more.