Without a master valve, once you turn the irrigation off those open sprinklers would continue to leak. With a master valve, turning off the irrigation would shut off the main water supply to the entire system and therefore those sprinklers could not leak.
Correspondingly, How do you turn off a master sprinkler valve? 
Why do you need a master solenoid? Why have a ‘master’ solenoid? Master solenoids (do not confuse these with ‘station’ solenoids) are required for retic systems that utilize mains water supply. A master solenoid is screwed directly onto the retic cut-in and only permits water to flow into the retic system when the retic is operated.
Furthermore, How do you replace a master valve?
Do you need a master solenoid?
Having a Master Solenoid is essential for any reticulation system for a number of reasons. In your reticulation system, a Master Solenoid acts as a fail safe.
How do you manually turn on a Hunter sprinkler valve? 
What causes a sprinkler valve to not shut off? 
Should my sprinkler valves be on or off? Make sure the sprinkler valve is closed, unless it’s the valve farthest from the main water source. You’ll want to leave this valve open and remove the sprinkler nozzle to allow air to escape when you turn on the water.
Should I use a master valve?
If your mainline is located in a place where a leak might cause severe property damage or a danger to the public, you should use a master valve. If you are willing to pay the price of a flow monitoring irrigation controller with a flow sensor, a master valve can be used as a water conservation measure.
Where do you put a solenoid valve? Positioning of the solenoid valve
- It is recommended to install the valve in a dry and ventilated environment. The valve gets hot during use. …
- Most solenoid valves can be used in one flow direction only. …
- The best way to install the valve is with the coil facing upward with a maximum deviation of 90 degrees (see picture).
How do you install a solenoid valve?
How do you replace a sprinkler valve without cutting it? 
How do I fix a leaky solenoid valve?
How do you troubleshoot an irrigation valve?
Should solenoid be on or off? Avoid over-turning the solenoid in either direction, as this can cause damage to the components or cause pressurised water to escape the solenoid. When you hear water rush through the device, it’s easy to tell that the valve has opened successfully.
How do you test a hunter solenoid valve? 
Can you manually open a solenoid valve?
One way is to simply turn the solenoid (the black cylinder with 2 wires) counter-clockwise a 1/4 to 1/2 turn. To shut off the valve, twist the solenoid clockwise until it is snug on the valve. The other way is to use the bleed screw the same way, loosen the screw enough to release air (1/4 to 1/2 turn).
How do you fix a sprinkler valve that won’t turn on? 
What causes a sprinkler valve to stay open?
The valves may have air trapped in them. A small bubble of air becomes trapped in the tiny water ports of the valve, this stops the water from flowing through the port. Since the water flowing through the port is what holds the valve diaphragm closed, the valve stays open.
What causes a sprinkler valve to stay on? One of the most common reasons for a valve to keep running continuously is the accumulation of debris in the diaphragm, which prevents the valve from closing. This video will teach you how to clean the diaphragm on your valve. The most common reason for a valve to remain on, or weep, is debris.
How do you fix a stuck sprinkler valve?
