There is an anti-syphon valve on which the inlet and outlet ports are configured in a U shape. Such a valve is normally required where ever the sprinkler system is connected to the water supply, even it is your private well. The anti-syphon valve is installed about 12" above the sprinkler piping system. A control valve usually has the inlet and outlet ports in a straight line. The easiest way to deal with these valves is to buy the exact replacement and swap out the internal components. If the valve body is leaking, try snugging down the screws evenly. If it is allowing water to pass through when it is closed, then it may need cleaning out only. Disassemble a valve carefully and observe how it has been put together. There is a spring, diaphragm, needle and a disc in there. Usually the diaphragm may need replacement and it is oriented only in a particular way.

The valves that are on the system are old, and I would rather replace them than try to fix them. They are anti-siphon valves and are in the U-shape you described. My question was, are all of the new ones the same size with the ports 3" aprart or do they vary? And secondly, how does one replace them. They are about 10" above ground.

The U-shaped anti-siphon valves are standard for all brands. If you want to replace them, you need to saw off the old valves and cement on new ones with the appropriate PVC piping. I would recommend using extendable PVC joiners between the old pipe and the new valves: they allow you to easily cement in the mating sleeves, then simply screw on the extenders to the old pipes and the new valve.

Lawn Genie are simiular to the Irritrol 2711 (3/4) 2713 (1") dpr or apr. You can replace the pop-it and the diaphragm if you would like or just replace the whole valve.

Here is a link that might be useful: How to change a diaphragm

To John, you mention an extendable PVC joiner. Where can I find that? I've looked everywhere. Is there a particular brand? Thanks

Carol, you can find PVC joiners/pipe fittings on eBay, Amazon and many other reputable companies, including your local home improvement/hardware store.

Here is a link that might be useful: PVC joiners & pipe fittings