pressure pumps

We are looking to installing a irrigation system at our lake house using lake water. Is is necessary to have a pressure tank with our pump or can we just use a pump large enough to carry the water to the heads. I have heard two different opinions. They say it is better to have a pressure tank so it will save the life of the pump. Then again the other opinion is that it is not necessary to have a pressure tank. Will it hurt the pump to run all the time while watering the lawn? Or will it save the life of the pump to have a pressure tank?
Thanks in advance for your opinions. Please help me.

You are correct, in that both options are viable. I think what you will find, as you do the research, is that it is not the overall run time that determines the life of the pump, but rather the frequency of starts / Stops. If you are using the pump for nothing other than irrigating your lawn using an automatic system, then a pump only solution would be what I would recommend. Most control timers have a Master valve/Pump channel, which in combination with a pump relay will turn your pump on when the timer starts irrigating, and off when it is finished. One start per cycle. Be sure to do your homework on the design, and match the output of each zone, to the amount of water output by your pump.

The way that you should match the zones to the pump is as follows:
1. Set up your irrigation system in zones; either one zone, or more than one zone with approximately equal flow in Gallons per Minute.

2. Select a pump that will be operating near its maximum efficiency point at the flow rate for the zones, and with a pressure that gives the required range for the sprinklers at that flow rate. You will want to look at a curve with pressure or head on the left (1 psi = 2.31 ft of head) and Gallons per Minute along the bottom. The operating point you want is probably near the manufacturers capacity rating of the pump.

3. Set up the system so the flow is never completely shut off when the pump is on. Ideally you would have a controller that opens the valve for the succeeding zone before the previous one is closed so you are never "dead heading" the pump. There may be enough mechanical delay in closing the valve so that the switchover can be made without deadheading. A second or so won't hurt if you have a a relief valve on the submersible.

Consider a submersible pump or a centrifugal "Irrigator" pump unless you have a very small area to irrigate. If it is a very small area you can use a shallow well jet pump, but they are quite inefficient.

The irrigator pump will require a foot valve and strainer in the lake and you will need to prime it the first time. It should be located as near to the lake as possible and as low as possible. You want to minimize the lift to minimize priming problems.

If you use a submersible you should put a relief valve on the line in case the controller ever fails to shut off the pump with the valves closed.

The Irrigator pump is best if you require a lot of flow, such as 25 or more gallons per minute. It is hard to find a centrifugal irrigator pump that provides adequate pressure and is efficient at low flow. A submersible with low pressure capability is the most efficient for lower flows.

The submersible will have a wire running with the pipe to the lake.

Try this reference before selecting anything. Irrigationtutorials.com check out the section on country bumpkin water. This will lead you step by step through the lake house irrigation. In answer to your 1st question, you do not need a bladder tank for the system. On a sprinlker system you want to run each head about 2.5-3.5 Gallons per minute. If you have 4 or more on a line youre into the 12 -15 GPM range. Your pump is going to run all the time you water without cycling whether you have a tank or not. Start and stops are what kill pumps. Pump relays on most sprinkler controllers lock in until all stations are cvcomplete eliminating cycling. Check the reference, its a good Saturday morning read.