Lake pump question

I'm reactivating an old underground irrigation system at my lake house. There are no sprinklers , just hose bibbs for standard watering, which I'm fine with.
Following a neighbors advice I'm using a 1HP submersible pump. The pump has an 1.25" discharge, which I believe is pretty standard, but the old system I'm tying into is 2". From the pump elevation to the highest hose bibb elevation is about 40'. My question is, am I going to have a problem with the excess water capacity that the 2" pipe has over the 1.25". Once that 2" pipe is pressurized am I going to have some type of gravity backflow pressure that going to hurt the affect the pump's capacity?
One more quick question, is there any reason I shouldn't just put pump on a manual switch and turn on when I want to use, as opposed to installing a pressure tank, which would a very problematic installation?

Thanks

You really didn't give enough info to make any decisions with. First of all, you didn't say which 1hp pump your using. They start out at around 4 gpm and go up to 30 gpm in increments. You didn't say how many of these hose bibbs you will use at one time or how many gallons per minute you expect to need when watering.

bob...

Thaks for reply, here's info I can gather
Pump is 25GPM

Performance curve chart shows 31 GPM at 60 Feet Total Dynamic head ( curve does not go down to 40')
A chart shows 24.4 GPM @ 40# and 40' depth
I'm hoping to run 4 sprinklers at once.

Thanks again

Standard big box sprinklers use around 2.5 gpm. (This is not to say yours do) So if you have a 25 gpm pump at your water level, your pump is overkill.

bob...

Thanks, Bob.
It is 25GPM, it's a well submersible pump.
Am I hurting anything with the overkill, other than using more electricity?

You could be cycling the pump to death unless you add a Cycle Stop Valve

bob...