W74 water running thru prewash tank

[Anonymous]

OK, I know this is fairly basic, but how do the water valves actually work on Wascomats (or other machines)? I know they have a electrically actuated plunger and a diaphragm, but how do they actually work. There are three tiny holes in the diaphragm and one little hole that the plunger covers. It just seems impossible that the tiny force from the plunger can hold the water back. What am I missing?

[CharlieS]

OK, I have to be careful about opening my mouth here, but I think this is correct.

The diaphragm covers both the water intake and the water outake. On the intake side of the diaphragm is a ventilating hole, which allows water into the sealed compartment above the diaphragm. In the center of the diaphragm is a pilot hole, which is larger than the ventilating hole, and which is normally covered by the solenoid piston, which is spring loaded to the off position. To cut on, the piston is energized and retracted, the pilot hole is uncovered, and water rushes out from above the diaphragm, releasing the holding pressure. The water at the intake edge of the diaphragm pushes it up and out of the way, allowing full flow. In the off position, The solenoid piston covers the pilot hole, with spring pressure. Water pressure begins to build back up above the diapragm, equalizing the pressure with the intake pressure. Once equalized, only a little spring pressure is required to actually hold it closed. The remaining pressure comes from the water intake itself, which is equivalently balanced against itself. A pretty neat piece of engineering which uses the hydraulics of the water and permits a low power valve design.

Charlie

[mike]

If I was smart enough to understand ANY of that explanation,
I would not be in the laundromat business !

[CharlieS]

Okay, its really just MAGIC !!!


I'm not sure I understand it either. Who the heck wrote that explanation? Its nothing but gobbledeygook.

Okay, imagine you drove your car off the dock and into the water, sinking immediately. You can't open the door, because of all the water pressure against it.

You break or crank down one window. You hold your breath as the car fills with water. The pressure is now equalized on both sides of the door, and it opens with just a little effort.

This valve works the same way. Water pressure holds it closed. When the piston activates, water flows to the other side and equalizes the pressure, allowing the diaphragm to open and let the water flow. It closes by reinstating the water pressure on one side, along with a little spring pressure.

The maintenance procedure involves cleaning the little waterways, which can clog.

BTW, this is why you should consider carrying a hammer or other tool to break a window in your car. If you end up in water, this is a very real scenario, and with electric windows, you have to break the glass with a tool. A little scary afterwards as the car fills with water, but the only way to get out. There are special hammers sold just for this purpose.

Charlie

[Anonymous]

Thanks for the explanation of the valve. That is what I thought happens, I am just a little confused on how it works to close the valve. It is shocking that one little tiny grain of sand can keep it from working.

[CharlieS]

Kirby - There is a difference in the size of the holes. The 3 small holes are still smaller in total size than the center pilot hole. The three small holes constantly let water to the back side of the valve diaphragm. When the center hole is opened, it is larger, and allows most of the water to run out, relieving the pressure on the back side, and allowing the front side pressure to push it open. When it closes, the back side pressure builds up again, equal to the front side pressure, and the small spring is all that is needed to push it closed.

Because the 3 small holes are small, the back side pressure cannot keep up with the front side pressure when the large center pilot hole is open.

[Anonymous]

You are correct on the "new" valves, but the one I just had a problem with was an old valve on a W124, it only has one hole in the diaphragm and one in the center. That is what surprised me.

[Lar Hylobates]

I carry the hammer in the trunk.

[Anonymous]

A straight pin works much better to remove the grain of sand.

[mr_soap]

Last night I found w74 with water running thru the prewash
tank. Door was open machine was off.

I turned off the water and power and left.

What should it check?

Thanks

[CharlieS]

Replace the diaphragms in the water valve. This is a quick job and a common problem. Always carry a supply.

This assumes that the water runs even if you cut power to the machine. If power makes a difference, then you have a different issue.

Charlie