Hi lawn nut,

Your pump should have a chart that shows pressure head versus flow rate. If you didn't get one with your pump in the manuals then your supplier or the manufacturer probably has one. This is not your concern really since for whatever head you are pumping against you are getting about 60 gpm. This has nothing to do with the 1/2" outlet except the water velocity produced by the pump is higher for a 1/2" outlet than a 3/4" or 1" line. Think of a fire nozzle that has very small diameter and the velocity is very large. Pressure washer use this principal as well. What reduces your flow rate is the mainline you use. Small diameter lines have more friction or resistance loss if they are long. Larger lines reduce velocity and have less friction loss. If you kept the outlet size, the water would be accelerated through that orifice but reduce velocity and friction loss in a larger pipe after the orifice. Turbulent flow is what you are trying to avoid so size the mainline pipe to keep the velocity to around 5 feet/second. There are pipe design calculation that give you the velocity. The irrigation design head flows(sometimes in GPH) for a given pressure can be added up and checked against your 60 gpm. You should only have the number of heads equal about 80% of you 60 gpm (3600 gph).
Find your pressure as well. At each irrigation head and pipe section there is head loss. This additive loss should also be about 80% of your system pressure.

maine_lawn_nut and lehua13 - Now I'm confused. I'd calculate this at 5 gallons in 55 seconds being equal to 5.45 gallons per minute, not 60 GPM. That seems like very low flow capability for an irrigations system to me.

I just checked mine by filling up six side-by-side 5 gallon buckets in 1 minute and 45 seconds = 17.15 gallons per minute. I used a 1/2 inch valve and six foot hose to do it so I'm hoping my actual capacity through the 1 inch system I'm installing (T'd off the main supply line) is higher than that. Have I messed up my calculations? Phil

Hi Lawn nut,

Yes you are correct and I made a mistake. I won't try to do any more math. That will be your flow through a 1" pipe just the velocity will be slower. It is what your pump can produce at that head (lift in feet). What is each irrigation heads rated and how many do you need? Aloha

Look at this first. Helped me greatly.

Here is a link that might be useful: Great tips to help get started

BL,

Excellent link site. It says it all. Aloha.

A 1/2 hp shallow well pump will only be good for about 8 gallons per minute for sprinkler systems which means you could PEE better! 3/4 HP centrifical pumps are A-1 for this job, providing you have adequate well point source and zone sizing, as in 15gpm per zone and 4 well points(sand), 5 would be better! providing a (minimum) of 5gpm each. This way you don't over pump the system and cavitate the pump and kill the wells and pump. IF your using a well casing, 3' or 4' you must have static water level not to exceed the 25ft range of the pumps lift!Jet pumps INCREASE pressure but pump less water meaning A LARGER PUMP!Hope this helps!!!

Before you get the idea to replace the pump with a larger pump, get your well tested. I looked into this. My local pump guy said lots of people upgraded their pump to a 1 HP pump. Higher flow rates started moving sand thorugh the pore spaces in the aquifer. After a year, the well only would provide about 2 gpm.

If you have the space for it, it may be worth buying a 4000 gallon tank (cheaper than a new well, more expensive than a new pump) Let the well keep this tank full, then use a secondary pump to run the irrigation system.