mosfet as a switch, manual over-ride switch?

Hi,

I have a mosfet that is used as a switch to control a solenoid valve. The mosfet is controlled by an Arduino.

Is it safe to add a switch between the drain and source to function as a manual on/off switch for the valve and will this be OK to use when the mosfet gate is high as well as low?

|500x370

That would turn the solenoid ON, but would fail to turn it OFF if the mosfet is conducting.

Add the manual switch between Source and Gnd. If the mosfet isn't grounded, your circuit will be open and the solenoid won't fire.

What is the purpose of the switch? - switch it off when already on or switch it on when already off? - keep it in the switched state permanently (toggle switch) or only as you press the switch (momentary button)?

You can't add a manual ON/OFF switch.

You can add however: - A manual off switch - A manual on switch - or on/off/auto switch ;)