planning to pump from a creek with jet pump.

hi guys
I'm trying to install a 1/2 horse GSW convertible jet pump with pressure tank from a creek to use for a couple of sprinklers to water the lawns.i dug a deep hole at the creek for the suction..the creek is running clean at this time of year....I plan to put the pump approximately 50 to 60 feet from the creek with a 12 to 15 foot head..the suction line is 1 1/4 inch ..I want to use a 3/4 inch discharge pipe to run 300'..the question is do you see any problems with this installation? any advice would be appreciated...thanks in advance.. oldgringo

I assume that you already own the pump and that it has a shallow well jet.

The characteristics of jet pumps are that they produce more pressure and flow if they are closer to the water. The difference between 5 ft of lift and 15 ft of lift is about a 25% reduction in flow at 40 psi. I would put the pump suction as near to the water as possible.

You should get 8 to 11 GPM (depending on suction lift) at 40 psi at the pump (My Goulds J5 pump curve). With 300 ft of 3/4 of Schedule 40 pipe at 10 GPM you would lose 30 psi. If you are using 3/4 poly it will probably be worse.

I recommend minimum 1" pipe, and maybe 1 1/4" if you want all the pump will deliver.

So my recommendation is:
1. Put the pump as low as possible and as near as possible to the creek, using a 1 1/4" suction line with a foot valve. Avoid elbows in the suction line.

2. Put at least a 1" line on the discharge (even if the pump is only 3/4"), and up to 1 1/4" if you want maximum flow.

A 1/2 HP jet flow drops off pretty quickly above 40 psi, even though the curves show it going to 60 psi with shutoff over 70 psi. You don't want to operate in that high pressure region.

thank you for the info..i guess i better rethink the installation.