12V Solenoid Valves
As we know 12v solenoid valves are typically used for simple ON/OFF control of gas or liquid media. A basic brass 2/2 way solenoid valve (2 port 2 position) valve when fitted into a pipework system will control the flow of media flow or no flow. In the case of a normally closed (fail-safe closed) solenoid valve when 12 volts is applied the solenoid valve opens allowing flow. When the 12 volts are removed from the solenoid valve then the valve will automatically close and prevent flow along the pipe. For a normally open solenoid valve then the opposite is true, i.e. the solenoid valve fail-safe position is open and when power (12vDC) is applied the solenoid valve will power close. 12 Volt solenoid valves are typically found in commercial applications, boat gas and diesel lines, car protection systems i.e. anti theft systems on diesel + petrol fuel lines with remote ON/OFF battery powered systems.
With a 12v 3/2 way solenoid valve you have 3 ports, typically 1 inlet port and 2 outlet ports for diverting flow. i.e. for valve actuator control, cylinder control, diesel to vegetable oil car conversion systems or controlling the air supply to an angle set piston valve. In some remote applications there is no power supply but there is compressed air, so by using a 12volt low wattage 3/2 solenoid valve to control the air line supply this in turn can be used to control (i.e. open and close) as much bigger valve in the system, such as a pneumatic angle seat piston valve.
12 volt solenoid valves are used for automotive, boat, commercial, shower and public display systems such as water fountains and water curtain display systems thus avoiding a potentially hazardous high voltage system with water or where no other voltage is available.
One notable point to consider is that most solenoid valve coils have a power rating rating from 5 watts as found in miniature 12 volt solenoid valves right up to 18.5 watts as found in some general purpose solenoid valves or even beyond to 100 watts for big bore direct acting (kick pilot) solenoid valves, so you need to be aware of the current draw. Remember watts = volts multiplied by amps (W = VA), so if you have only 12 volts the ampere or current requirement will escalate. For example 12 volt solenoid valve with 15 watt coil will draw 1.25 amps and if connected to a battery will have a significant power drain and will need topping up according to the power usage. Amps (current consumption) = watts (power consumption of coil) divided by 12 volts.
One way to avoid constant power drain when energising a 12 volt solenoid valve for long periods of time is to use a 12v latching solenoid valve. In this instance only a very short electrical power pulse typically less than 0.2 seconds is required to change the state of the solenoid valve i.e. from open to closed or visa versa. In this way power consumption is greatly reduced saving battery life. However, typical latching solenoid valves will require a reversed polarity electrical pulse to change back.
Example of latching solenoid valve function would be a fast power pulse of 12 volts to open the solenoid valve, the solenoid valve internal magnet keeps the solenoid valve open allowing constant flow without the need for electrical power supply. Now to close the latching solenoid valve the positive and negative terminals are swapped around and the next power pulse cancels the magnetic field allowing the solenoid valve to close and prevent flow.
When using 12 volt solenoid valves out doors be sure to cover the solenoid valve and protect it from the elements. Good quality solenoid valves will have an IP65 protection rating which means when installed correctly they are safe from even powerful water jets from any direction, however damp will ingress over time and can cause the coil to short circuit even after only 12 months.
Helpful hint: Weather proof the solenoid valve, have the cable entry from the ground upward into the electrical connector and clamped correctly onto the cable, fill the connector and sealing faces with some silicone sealant and try to shield the solenoid valve to reduce its exposure to the elements. In the long term this will save time and money.