review of pump HP

Need review of what horsepower does on pumps.
I have a well, 29' below where the pump will be. It now has a 2hp Sta-Rite pump on it.
I'd like to put a 1.5hp Sta-Rite on it, because of economics.
Does the HP of the pump relate to how much suction it has, or does it relate to the number of sprinkler heads I feed with it?
If it relates to number of heads I feed with it, I know I can get by with a smaller number of pump HP. I have 3 sections of 4 heads ea.
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A pump doesn't really suck. It just reduces the atmospheric pressure at the inlet. The lack of atmospheric pressure at the inlet will push water into the inlet. Atmospheric pressure is about 14.7 pounds per square foot.
With the maximum 14.7 pounds to work with the practical maximum for the best of pumps is about 25 feet. This 25 foot design would not be easy to prime, and would not be easy on the impeller long term.
You would be better served with a submersible or some sort of jet pump.
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On Sat, 02 Jan 2010 11:01:49 -0500, snipped-for-privacy@mucks.net wrote:

All the above was assuming a non jet pump. If your Sta-Rite pump is a jet pump design the ignore the above.
HP relates to volume not vacuum.
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On Jan 2, 11:10 am, snipped-for-privacy@mucks.net wrote:

The answer is all of the above, plus other factors like how long the pipe runs are, how large diameter pipe, how many GPM the heads are, what flow rate the well can support, etc. I can tell you this. I recently had a 1hp submersible installed on a 50ft well. The water depth is about 40ft below ground level. It serves a 10 zone system, where the largest zone has 10 heads doing 15GPM.

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Summarizing everything that's been said, you can't tell from what you've presented. For example, what is the flow rating of the heads you are using? Do you plan on expanding the system in the future? Does your system use a pressure tank, (high pressure, low volume pump), or no pressure tank (high volume, low pressure, continuous run pump)? From your description it may even be that the smaller pump is preferable, if the larger one is oversize for the application -- more likely to heat up because there isn't enough water being pumped.
We recently had to fix a system that had a mismatch between pump size and application - the original DIY'er had put in a large pump (future planning) but a small pressure tank. Worse, the pump was high volume, low pressure, not matched to the pressure tank. If you could stop the pressure switch from chattering, it would fill the tank in seconds, then shut down while the tank bled down during irrigation, but restarting after only a minute or two of operation. We fixed it by replacing the original pump with a high pressure low volume pump and replacing the small pressure tank with a 100 gallon hydro-tank. Now the pump runs for 3-4 minutes, then shuts down for about half an hour. We also could have removed the pressure tank and operated the irrigation system directly from the original pump, but there was an outdoor sink at the green house that we didn't want to have to replumb.
In your case, I'd take the information on my system to a local irrigation systems supplier and get their advice. You'll probably find that they can steer you in the right direction, avoid buying the wrong items - and that their products are as inexpensive and probably better quality than what's available at the box stores.
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