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Son of Samurai's Blog

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Can Low Water Pressure Cause Solenoid Valves to Leak?

Son of Samurai

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We run into water inlet solenoid valves in many different situations -- washers, dishwashers, refrigerators -- so it's important to have a firm grasp on exactly how they work. For example, I just talked with a tech recently who was wondering why low water pressure can cause inlet valves to leak.

It seemed counter-intuitive to him, and he's not wrong. Wouldn't it make more sense for high water pressure to cause leaking? But once you learn exactly how these valves work, it will all make sense.

First, the solenoid part. To boil it down, all a solenoid is is a coil of wire and a shaft that fits inside the coil. When current flows through the coil, it produces a magnetic field, which pulls the shaft into the coil and holds it there. Simple as that. If you put a plunger on the end of that shaft, then you've got the moving component of an inlet valve. When current flows through the valve coil, the shaft and the plunger lift, allowing water to flow.

That explains how the valve opens. But what about closing again? For this purpose, there's a spring that pushes the plunger back into place once the solenoid deactivates.

But keep in mind that this plunger has to make a tight enough seal to keep water at high pressure from leaking through. A little bitty spring isn't going to cut it. The simple solution to this is to use that high pressure to the valve's advantage. See the diagram below:

Direct-acting-solenoid-valve-working-principle.jpg

You see, the water is actually allowed to fill the space above the plunger. That means that when the valve isn't energized, the water pressure helps make the seal that keeps water from getting through the valve. Pretty nifty!

So now you see why low water pressure becomes a problem. Typically, water inlet valves have a minimum spec of 20 PSI. Anything less than that, and the water pressure just isn't enough to make a reliable seal. That's when you get inlet valves "weeping" -- letting a small, slow trickle of water through. Not a problem with the valves themselves, but with the water pressure coming to them.

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Great illustration!

Is there an easy trick to find out that the water pressure is below 20 PSI, before ordering the new valve?

Thank you.

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rasputista

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Beware of Reverse Osmosis systems on fridges causing dripping and ice maker problems, the customer has to get a booster pump.

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Jedi Appliance Guy

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It's a common issue down here in South Florida. The Snowbirds go back up North. They shut off the water to the house at the main. The house plumbing will loose pressure over time (less time if there's a plumbing issue like a leaky toilet flapper) and one of the solenoids in the house, either the dishwasher, the washing machine or the refrigerator, will let go when the pressure falls below the threshold and release the remaining water pressure in the house. 

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