It's definitely a good idea to blow the water out using a compressor. Since naturally there will be sections of the system where water will sit, and the pipes are not very deep (typically 1 or 2'), they will likely freeze, and if that happens the pipes will crack, and you'll have a non-working system (and lots of digging to do) in the spring.
Check this question for advice on how to connect a compressor to the sprinkler system. It's best to blow out each zone one by one, so that you don't end up with water stuck in one line still while all the air escapes out another already-empty zone. Start with the zone with the highest elevation, if possible, and go down from there. You may need to cycle back through one more time.
Once you have the fittings ready to connect your compressor to the system, it's a pretty quick job, should only takes a few minutes really. Once there is air coming out of the zone, you're good and can move on to the next.
50 PSI is about the max you'd need on the sprinkler system side. Be careful going higher - 100 PSI is probably higher than the pipes/fittings used for sprinklers (or the sprinklers themselves) can handle.
"Cycling" in a pressure system is generally when the pump is turning on and off too quickly. Pressure systems are specifically designed so that the pump runs up to its maximum pressure, then you use water from the pressure tank, until it reaches the minimum pressure, at which point the pump turns back on and runs until it reaches the maximum.
The recommended minimum run-time for a 1-2HP pump is usually 2 minutes. How you get to that is based on the flow rate of the pump, and the size of the tank.
Based on your 150gallon tank, and not knowing your flow (in gallons per minute, GPM), based on this tool here's some example flows/times:
- 16GPM: 3 minutes
- 20GPM: 2.5 minutes
- 24GPM: 2 minutes
As you can see, the higher the flow rate, the shorter the pump will run.
In your case, it sounds like one zone is basically matching the flow rate of the pump (you could verify this by watching the pressure gauge while it's running, it should be fairly steady). While this may reduce pump starts, if you use water elsewhere at the same time, your pressure will drop and the pump will not be able to keep the pressure as high.
Now, the flow rate the pump puts out depends on a couple things, most importantly: the pump itself (and now many stages it has), and the depth to the water level. Each submersible pump will have a chart showing the flow rates at different depths, so you'll need to find your model and the water level to figure this out. Here's an example though, using a 2HP pump I found while running at 60psi (depth to water: flow rate):
- 20ft: 23.9 GPM
- 60ft: 22.7 GPM
- 100ft: 21.3 GPM
At first glance, this seems fine. My guess right now is that your first zone matches the flow rate of the pump, while the second zone is simply a lower flow rate than the pump. It's no problem, things are designed to work this way.
If you really want to reduce the cycling, you can hook up a bigger or a second pressure tank. This will give you more capacity, and so the pump will run longer, but it will also stay off longer while you use water stored in the tanks.
Now, if you had fast cycling (eg, <2 minutes run time) or "rapid cycling" (a couple seconds of runtime), then that would indicate a problem with the pressure tank. Normally the tank should be pre-pressurized at 2psi below your cut-off (low) pressure point - so in your case 43psi. To check this, you'll have to turn off your pump and let the water drain out (open a tap somewhere). You can top it up with a normal air compressor.
Best Answer
I have found broken pipes by using a dowel pressing to the ground then pressing my ear to the dowel, if there is water ruling you can hear it 5/7 heads is not that many and if there are no isolation valves it probably worked fine in the past, being built in the 60’s it is probably galvanized pipe, there are many possibility’s for low flow. The first a broken pipe you have thought of, galvanized pipe also can corrode and build up on the inside limiting the flow of this is the case the pipes will need to be replaced and the pipes are old enough for this to have happened, the third thing I think of is the sprinklers may be plugged with sediment (or possibly a screen filter in line is plugged) so there are a few things to check, you stated you don’t know where the well is you can run water inside the home and use the dowel method to find the pipe (normally the well casing extends above the ground but I have seen a few that were buried (not good). Hope this gives you a way to figure out what the problem is.