Need help with Solenoids.

Yes, I know.... "search the web".

The problem where I am stuck is pump, solenoid, pressure and cost.

This is already costing a bucket load of money - kind of - but a recent development has blown the whole thing out of the water, so to speak.

I was going to get a cheap pump with not too much of a flow rate as the pipes are not going to be closed at the ends. They will simply drain into the plant pots.

Each plant will have its own pipe. Thus solenoids for each plant.

PROBLEM: The pressure out of the pump is not enough to close the solenoid. It seems the solenoids need pressure to close them.

Getting solenoids that don't need pressure cost big $$$$. Getting a pump which can supply the pressure to make the original solenoids close also costs $$$$ compared to the pump I was going to get.

What other methods are there to "switch" where the water goes?

Have you tried reversing the water flow connections on the solenoids. Solenoids should, if anything, need pressure to open - not pressure to close.

Well, at this stage, I don't have any.

I am pricing them and getting the specs.

The ones I am wanting are normally closed, and with 12v DC they open.

So the power opens the valve.

Removing the power - I thought - closes them.

Alas not all. And the person with whom I was talking say those kind cost.

In the mean time I have "discovered" washingmachine solenoids. They seem to be what I want, though they don't exactly have an ouput thread. It is more a spigot. But that would suffice. I just use smaller pipe.

I have sent off a request to a supplier, but what I am asking is not the usual questions so I am not holding my breath for a reply.

Ah, the quest continues.


You can buy washing machine solenoids as spares, e.g. in the UK from The snag is that they may be 115v or 230v AC operated and therefore need an SSR to drive them.

I have found some local and are 12v DC.

I am still waiting on the specs for them.

Fingers crossed.

Just to be clear here, we are talking "solenoid valves" - the standard design is regenerative using fluid pressure to amplify the effect of the solenoid via a diaphragm - these require the difference in input and output pressure to be within specified limits to work - they just open otherwise.

Beware the wikipedia entry on solenoid valves, it doesn't explain their operation correctly.


Thanks very much for the post.

Yeah, I have since leared what you said.

THOUGH! And here's the interesting part......

My washing machine has solenoids. They run on 12 v DC. (Well maybe not, but the ones I have my eye on do.)

Having the tap fully open they work, but when they "close" (as in STOP water) there are problems like "water hammer" in the pipes.

So I turn down the pressure.

I can turn it down so low, the water is hardly trickeling into the tub. I'd call that no pressure.

They stop the water flow when I open the lid.

So I am concluding that they would work for my needs.

Your thoughts?

They are appreciated. I NEARLY did buy 5 of them but luckily the person was honest and realised the ones I was going to get would not close when I de-activated them.

They may have a pressure-reducing valve upstream in the washing machine, or rely on a length of rubber pipe to absorb the water-hammer - I would expect a solenoid valve to be very sudden in its switching since it is the physical analog of a schmitt trigger (positive feedback).

i found for you some small cheap ones take a look here :