Common Shut off Valves
These are typical irrigation shut off valves normally located where the water main enters the house or building.
You may have multiple valves that look like the ones below. If you think you know which one it is you can trace the pipe from the "outlet" side of the valve to where it exits the building/house. Normally it will exit above ground and outside on the other side of the wall will be your valve box and winterization point.
(To check if you open the hose bib attached to the system or manually turn on a zone it should not come on and you should still have water for the rest of the house)
The Double Check Valve as shown is how it needs to be for the Spring Turn On service. For the Winterization either one or both need to be turned to the "Off" position which is a quarter turn clockwise so the handle(s) are perpendicular to the pipe.
Valve to the left is a standard ball valve. "On" position for spring and "Off" position for winter.
Older systems may have a gate or globe valve as shown on the right. Same applies. Turn clockwise to "Off" and counterclockwise to "On".
One or more of these can usually be found where the irrigation main exits the building or house as well as other areas of the property. These should be kept clear of grass and mulch. They can be very difficult to locate for the mechanic if hidden.