This is something I got curious about in the course of diagnosing this issue.

Our washing machine has a couple of electronically controlled valves on its intake (I believe they're called "solenoid valves"). Based on observing the flow of water into the block above the detergent/conditioner drawer, they each appear to be able to function in two modes:

  • A "full bore" mode, where water gushes into the machine and shoots into the channels above the drawer and from there down into its compartments.
  • A "trickle" mode, where the valve is presumably partially open and the flow is much less. It seems to be deliberately restricted so that the flow falls down at back of the drawer, bypassing the detergent/conditioner compartments.

Each valve seems to be used in both modes at some point in the longer machine programmes. Typically both are opened fully simultaneously to fill for the final rinse.

When I first saw the "trickle" being used, I initially assumed the valves must be sticking, but it's used with exactly the same timings each cycle and seems to be quite intentional.

My questions are:

  • What voltage do these things typically operate at?

  • How is the valve's flow-rate controlled, given they seem to be capable of more variation than simply on/off? Is it via the voltage level, or the polarity, or something else? (There are only 2 wires going to each solenoid).

Googling around finds me a lot of replacement parts for sale, but I cannot find any concrete specifications for any of them which would actually answer the above!

Here's a picture (the machine is an AEG L69480VFL, but the parts for most machines look so similar I'm guessing they all operate in a similar manner).

Washing machine intake valves

Update: I found an image on a spare parts site of what I am pretty sure is the same valve. I think that makes it clear what the voltage is: AC mains level. Although, if it is AC, that makes it more mysterious how each valve seems to be able to support two different flow levels though. (Will definitely now take this one to Elec.Eng SE, as suggested in comments below).

Intake solenoid valve

Update: In response to a comment on an answer below...

The pattern of valve operation on the machine's shortest wash cycle is (left/right as looking at the machine from the front):

  • Fully open left hand (green topped) valve. Water flows to right hand side of the plastic block above the drawer, which squirts it leftwards to the channels above the detergent compartment.

  • Apparently partially open right hand (brown topped) valve (or if it's not the valve partially opening, something else is acting to restrict the flow to less than it can be). Water has insufficient pressure to get into the channels above the conditioner compartment (I think this is "by design") and drops down at the back of the drawer to fill the machine. However with our low water pressure there are repeated fill timeouts. And with the restricted flow this stage is insufficient to activate a 0.5l/minute flow-activated pump.

  • Fully open right hand (brown topped) valve. Water has sufficient pressure to get into the channels above the conditioner compartment and flush/syphon the conditioner into the machine. I am virtually certain the transition to this stage is under control of the machine: it happens with the same timing, and the machine does some rotations then a drain between the two fills; it's clearly not a stuck valve just deciding to fully open after a while.

  • Fully open both valves for final rinse fill.

On longer cycles, the left hand green topped valve also seems to used in partially open "trickle mode" at one point but I forget exactly when in the cycle; possibly it was used as an initial stage to wet/"pre-wash" the load before using the full flow which would draw in detergent.

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    A) this might be better suited for Electrical Engineering, B) I find it amusing that those black feed tubes are crossed. It's like group a designed one part and group b designed the other, then they put it all together and said "oops!". – FreeMan Jun 23 at 16:54
  • @FreeMan: Yes I raised an eyebrow at that crossover when I first opened the machine. The tubes and the nozzles they connect are actually a slightly different diameter, so it's quite deliberate! (Guessing the different diameters are actually a guard against assembly folks connecting them the "obvious" straight-across way). The Elec.Eng site is a good idea; will try it over there if nothing comes up here in a few days, or noone migrates it for me. – timday Jun 23 at 17:07
  • I've requested a migration - keep an eye out. – FreeMan Jun 26 at 15:20
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    The crossover allows the pipes to flex more easily under vibration, as they are already flexed. That maybe one reason for it. – SiHa Jun 26 at 16:56
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    If you can afford to waste some water for the sake of science: set up something to bleed just enough water to keep that flow-activated pump active, then try running the washer. If you know the timing of the washer's cycle you could open the bleeder in anticipation of each water fill step and close the bleeder when the machine has opened its valves. It might be interesting to learn how the valves behave if the pump is already active when the valves open. – Greg Hill Jul 1 at 17:42

It's difficult for me to imagine that these valves are truly intended to operate in the "full bore" and "trickle" modes you described. I think it's more likely that the "trickle" mode is actually a malfunction.

After reading a little about the differences in operation between direct-acting solenoid valves and pilot-operated solenoid valves at Burkert and at Instrumentation Tools, and also reading your linked question, I'll venture to guess that the valves in your machine are pilot-operated and that your water supply pressure is sometimes so low that the pilot operation fails. Maybe the water pressure vs spring is so low that the main valve opens only partially, or even not at all and the trickle is just what flows through the pilot.

The situation mentioned in that linked question, in which a flow-activated pump is installed to feed the washing machine, is interesting. But I think it's consistent with the theory above. As the pump is flow-activated, it does not provide any boost in pressure until after the valve has opened enough to allow sufficient flow. Thus the pump does not provide any additional pressure at the time the valve should transition from closed to open, and in fact probably is a pressure loss, further impairing the ability of the valve to open in the first place.

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  • Thanks. This interpretation of the observed phenomenon is looking more likely the more I learn. The thing which puzzles me is how consistent the flow pattern is across repeated use of the machine. I'd expect any sticking of the valve or a marginal pressure & flow resulting in the pump triggering or not triggering to be more random, whereas the "trickle" vs. "full" flow modes seem to occur precisely repeated to within a minute over a 30min wash. It's very strange. I need observe it some more with the above in mind I think. – timday Jun 26 at 22:12
  • Does the machine sometimes operate both valves at the same time? That might be a factor. – Greg Hill Jun 26 at 22:17
  • Added a description of the valve opening pattern to the question. They are used simultaneously for the fill for a final rinse, and that's the only time I've seen them both open. Presumably at that point the detergent and conditioner drawers have been consumed and there's no need to bypass them by trickling water in more slowly. – timday Jul 1 at 15:04

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