Introduction: Automatic Water Level Control From Washing Machine Parts

By Ted Gresham
About: I am an erstwhile Trailerpark Scholar, tinkerer, student of life, graduate of the school of hard knocks.... with a couple of tech schools and a college degree tossed in. I live in Lufkin, Texas, with my wife…

My little hydroponics system uses a 55 gallon barrel for water storage. Water flows from the barrel through the plant trough by gravity and is then pumped back into the barrel. Any system is prone to leaks. Mine is more so than some. I have drips here and there from my plant trough. Evaporation and the plants themselves draw water from the system, too. I’ve had to add water ever couple of days to keep the level up.

We’re planning a vacation, however, and there’d be nobody to keep the barrel full. I needed an automatic system to do the job for me. Recently I disassembled an old washing machine and had the parts at hand that I needed to make an automatic system. A couple hours’ work this morning and now I have a system that will keep the barrel full while I’m away.

Here's a narrative description of this project.  I've added pictures with descriptions to help explain.  This project is one that will require a bit of hands-on know-how.  It can be adapted to an assortment of applications but the basics of how the system is constructed and how it works is about the same.

Most every washing machine has two controls that together will do the trick quite nicely. Washing machines control the water supply with an electric solenoid valve. They use a pressure switch to control the water level in the tub. Those two devices together are what is needed. The solenoids are on the back of the machine. The pressure control is most often in the top of the machine with the other controls.

It’s really a rather simple system. All that is required is wiring the solenoid with the pressure switch in the circuit to cut the solenoid on when the water is low and off when the water level reaches maximum. As usual, I scrounged for most of what I needed. I used a couple of old extension chords for the wiring and an old piece of water hose for the water supply.

The solenoid control has two valves that controlled the hot and cold water for the machine. I used only one. The valves are normally closed so there’s no problem with the other side leaking. Solenoids have spade terminals. I took a six foot (give or take) electric chord and put two female connectors on the end. I then took a longer chord, about 15 feet, and put spade connectors on both ends. I attached one of the spade clips from the power chord to the solenoid. The other I connected to one side of the pressure control wire using a small piece of metal. I could simply have connected them with a wire nut but by using the spade clips I made disassembling the system easier. I connected the other lead from the pressure switch wire to the solenoid. Then I connected the other end of the long chord to the pressure switch using the spade clips.

A washing machine pressure switch is a simple device. It has a length of rubber hose that is lowered into the water supply. Water pushing up into the tube creates air pressure that moves a diaphragm that turns a switch on or off. Some machines have a simple pressure switch that is normally open but closes when activated by rising water in the tube. Those will have only two terminals. Mine had three terminals attached to a double-throw switch inside the control. I had to use an ohm meter to figure out which terminals to use. I connected the wiring to the side of the switch that is open until the diaphragm is activated by rising water level. It’s easy to activate the switch to test it. All one has to do is blow in the tube. The control clicks when the switch is thrown. (Note: if one knows a bit about wiring and has a double-throw switch like the control I used the other terminal could be used to wire in a low water alarm. That is another project, however.)

Some pressure switches have a level control, a knob that adjusts when the switch will be activated. The one I used had a three-position knob. This knob determines how sensitive the switch is. I checked each setting until I determined the best one to use so the switch would activate the quickest. Older machines have simpler valves with no settings at all. I have in my junk box another pressure switch that is simply an enclosed diaphragm/switch and two terminals.

I completed the wiring on my work bench before taking everything to the greenhouse. I mounted the solenoid control high on a wall near the roof of the green house above an electrical plug. I made a mounting bracket by flatting and bending a piece of electrical conduit. I used a length of old water hose for the supply from the solenoid control to the water barrel. I used one of the washing machine hoses for the water input. A garden hose will screw right into the other end of the washing machine hose for the water supply.
I ran the hose from the solenoid and wire for the pressure switch along the ceiling of the greenhouse to keep it out of the way. The wire and hose drops down from right above the barrel.

Getting a pressure switch to work properly takes a little bit of fiddling with the rubber tube that controls the switch. The tube has to be lowered carefully down into the water so water rises in the tube pressurizing the air in the tube as it rises. I fastened the rubber tube around an old pipe, actually part of an old tent pole, using a wire tie at each end. The hose was too long to go straight down so I wound it around the pole. The pole holds the tube down into the water and allows for adjusting the depth of the hose at the same time. The switch will not work properly if the tube is cut off. The full length must be used.

When I had everything in place I worked with the turns of the tube on the pipe, lifting it and lowering the control into a full barrel until it cut on and off at the right places. The control should click on when lifted from the water six or eight inches and off when lowered to the appropriate level for full. The distance between cut on and cut off may differ depending on the particular control and tubing configuration. The tube must be configured to work with the depth of the water tank. In a deep tank the tub can simply be suspended straight down. When the tank is not deep enough, as in the case with my barrel, the tube has to be coiled.

I hooked up the water, plugged in the power, and lifted/lowered the pressure control to make sure the water flowed correctly. I secured the pressure control inside a plastic freezer carton just so the terminals would be protected a bit. With everything working I secured the pressure switch on the top of the barrel. Project complete!

Some might say the one disadvantage of this system is that it uses high voltage (110v household current) in a damp environment. This is true but if the wiring is done right and properly covered where necessary there shouldn’t be any problem. I would note that anyone attempting to make this system should know a bit about basic household wiring. The wires should be secured well and not strung where they might be caught, pulled or cut by something.

This project didn’t cost me anything to make since I had everything I needed lying around my shop. By scrounging the solenoid valve, pressure switch, and washing machine hose from an old washing machine and dig up an old water hose one can build this system for a few bucks, the cost of a couple of cheap extension chords and some spade connectors. It works just as well as a much more expensive system bought commercially. Now it’s time to figure out where we can go on our vacation with our tiny little budget!