Yes, where you tap into your water well system does matter. If you tap into your system before the pressure storage tank, it will eventually not only effect your household water pressure but can lead to eventual pump damange. The "Tank" is not only a storage tank for water, but also your hous water pressure. Most storage tanks work by holding water and vapor pressure in the tank for use when someone opens up a valve inside the home. Once a tap is opened up, water moves from the tank to the point of opening and at the same time the pressure in the tank falls. Once the pressure falls below the set point of the pressure regulator, it starts the pump and the tank begins to refil. Since the water line from the tank to the pump is empty, the first thing that enters the tank is vapor pressure. Once all the air has moved from the water line to the tank and the line fills with water, the tank begins to fill. Once the water demand has ended, the tank will continue to fill until it reaches the set point of the pressure regulator which will trip, turning the pump off.

A check valve which will probably be installed on the water line coming into the pump, but close the the pump will close, preventing water from the tank draining back into the water line. A air valve (looks similar to valve stem on a car tire) opens up and allows air to enter the water line which releases the vacuum in the line and lets the water in the line to drain back down into the water well.

When additional demand for water happens, this valve closes and the pump is activated, and again the air that is now inside the tank rushes into the tank ahead of the water. This air creates a vapor space inside the tank which creates a more constant water pressure inside the house. Without this system, your water pump would kick on every time someone opens a tap inside the home, and would cause the pump to run unneccessarily. This will shorten the life of the pump dramatically.

If you tap your irrigation system into the water line upstream of the tank, and you turn your irrigation system on, you will get an initial rush of air out of the spray heads and eventually water. Once the watering stops and the valves close, the water line will not be able to refill with air. Thus, once water demand happens from within the house, the line will still be full of water and will not refull the tank with air. Eventually your tank will become water logged and your water pressure will be effected which will cause your pump to run all the time.

Sorry for the long reply, but couldn't find a short version of explaining this.

Sincerely,
Curtis Anderson
Evergreen Sprinklers

Here is a link that might be useful: EvergreenSprinklers.com

Curtis does explain well how a pressure tank and well system works, but his last portion regarding air in the lines seems to be a little misguided.

Most pressure tanks installed in the last 20 years are actually a rubber balloon inside a steel tank. The air pressure is on the top side of the balloon filled with water. This prevents air from ever entering the system. (if the bladder is not damaged) You will need to add a backflow preventer to your system, to keep water from re-entering your household system.

You can tap your feed pipe before it hits your pressure tank if your only check valve is at the well head. It is standard procedure to add hydrants between the well head and pressure tank. I suggest contacting the company that installed your well and ask them.

I just bought a house, My system looks rather old maybe not,it seems to have probably a 3 to 5 gallon tank on top and on the side it says that "2o Psi is factory PRECHARGED"
100 psi is continuoslly and max.
What does this all mean.
With the motor not running what does the pressure need to be at, it is at 24 PSI's at idle.
My problem that brought me here is that my "water pressure" seems to be pretty low, but increase's dramatically when the pumps kicks in...[1/2" HP by the way]
and it turns on Imediatlly when a hose is used, or every 1.5 minutes of constant use. Thanks

Bigham,
What all this means is that with the system drained (pump off, all water drained out) there should be a 20PSI air pre-charge in the tank. Typically, the pre-charge is 2PSI below the cut-in pressure (set by adjusting your pressure switch). According to the info you gave, your pump should turn on at 22PSI, and shut off around 42 PSI.
Be aware that the most common pressure gauge is the "air-filled" type, which are notoriously inaccurate. Invest $20 in a glycerine-filled gauge for the system and a good-quality tire pressure gauge to check the tank pre-charge pressure.
You don't mention the size or type of pump so I can't really address the low-pressure issue other than to recommend checking your tank pre-charge and cut-in/cut-off pressures. Again, pump should turn on 2 psi above pre-charge pressure and shut off about 20 PSI higher than cut-in pressure.
Also check to see if your tank bladder has become waterlogged: push in on the Schrader valve on the tank - if only air escapes, you're probably good to go. If any amount of water sprays out, replace the tank.

BK

Everything explained above has some merit within. However, the best solution to your problem is to add another pump for your sprinkler line (assuming you have a resevoir) with an automatic pressure switch/valve if you can afford the additional cost. The number of stations will depend on your well flow rate. Doing this will save you a considerable amount future cost and time. Curtis