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Author Topic: Motorizing a valve, which of this two options is better?  (Read 2071 times)
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Hi, I need to motorize a 1" valve and I have two valve options.

Ball Valve:


Globe valve:


I can´t decide which is better, Ball valves have only 90 degrees of movement, but are harder to move, I was thinking of using a Servo, probably the TowardPro Mg996r which hace 12-13 Kg-Cm, but I really don´t know if its enough. It have metal gearing but plastic enclousure and arm.

The second option probably I will need a servo with continuius rotation, But the problem that I see is that the wheel will move up and down depending if its closing or opening the valve, so I can´t figure out a plan to fix the servo in one position. I don't have a lot of gears or equipment.

Which one do you recommend? Do you think a servo with 12-13 Kg-Cm can open the ball valve?
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You'll need to measure the torque yourself - then allow a heathy safety margin (factor of two or three perhaps?).  Measure the force needed to pull the arm, multiply the force by perp. distance from pivot.  Piece of string and a weights pan might be the simplest.

For motorising the globe valve things will be more complex as the end-stops can only be determined by measuring the torque or stall condition.  You have to avoid over-tightening yet be able to supply a larger torque to reverse from the end-stops (such valves bind when closed, more torque is needed to un-stick them due to static friction).

Offhand I'd say you could use something like a motor with a series resistor.  You normally power via the resistor and monitor the current by measuring voltage across the resistor - this allows you to detect when the motor stalls (endstop).  To then reverse back you briefly bypass the resistor to get more current/torque to start the motion again before going back to current-monitoring mode.  So having an H-bridge supplied via a load resistor with a high-side switch in parallel to the resistor might be one way.

As for the mechanical issue, the motor would need to either be in a frame than can slide up and down with the screw-thread motion, or (perhaps better) done via a reduction gear with the pinion long enough to cope with the along-axis motion.

Another method is to have the motor drive a set of prongs that go into the holes in the hand-wheel - easily removed and allows manual override.

Note that if you have two much reduction-gearage it will be hard to measure / limit the torque to valve, too little and the motor will need be over-powered.
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How about option 3, the way it's done in the real world: a solenoid valve?

Google "sprinkler valve" or "solenoid valve", or just walk down the plumbing aisle of your local borg and look for the sprinkler valves.

I'd probably look for a model that will operate on 12VDC, since that's pretty easy to come by and it's a well-documented arduino-level switching problem.

When figuring out your arduino circuit, treat it like a big relay, only for water.

-j
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As well as solenoid valves, you can also get 1- and 2-way motorised valves of the sort that are commonly used for central heating and hot water systems.
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Yes, first you have to decide if you require the ability to control the amount of flow or is full on/full off good enough for your application?

Lefty
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look for the sprinkler valves. I'd probably look for a model that will operate on 12VDC

I wish they made 12v sprinkler valves, but 24v are the only ones I've seen.
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Which one do you recommend? Do you think a servo with 12-13 Kg-Cm can open the ball valve?

I doubt you will find an inexpensive servo (how much are you willing to spend?) to turn the ball valve. You may have to go with a sink valve as they are easy to turn and usually half a turn goes from full open to full closed.
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look for the sprinkler valves. I'd probably look for a model that will operate on 12VDC

I wish they made 12v sprinkler valves, but 24v are the only ones I've seen.

24V will work just fine. Whatever is cost effective and available.
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I wish they made 12v sprinkler valves, but 24v are the only ones I've seen.
I just did this for one of my own projects.  The average 24v solenoid valve should operate just fine on 12v wall wart switched with a 2n2222, at least three different ones did for me (Lawn Genie, Toro, and rain Bird).
« Last Edit: October 22, 2012, 01:00:26 am by seanz2003 » Logged

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Thanks for your help, I analize all of your answers. Unoftunately 1" selenoid valves are expensive and sprinkler valves are impossible to use for my applciation because I need to close and open the valve with or without pressure across the valve, sprinkle valves usually need a pressure in the system to open and close and in my project the pressure is very low.

I resolve this problem with the ball valve and a servo, I use a cheap 11 Kg-cm servo and until now is doing just fine. Probably I will need to change it in the future for another of better quality or stronger.

Thanks again!

 
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Depending on the application you may be able to use some silicone "plumber's grease" on the ball in the valve to make it turn easier.
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Thanks for the advice!
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Hey travis12,
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use a cheap 11 Kg-cm servo
Where'd you get it? The power and gears sound impressive but I saw one review on Youtube that was interesting.

- Scotty
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Hi scotty, I use almost the same servo of the review, I get the MG996R. I saw the review too and a lot of comments in forums before bought the servo, after all the research I also believe this kind of servos are not very good for RC application where centering, overshoot and speed are very important features (or your RC plane or car crash and get destroyed). The most extreme case I found was someone who claims his servo get in fire.

But for my application and budget(similar servos of better brands costs almost three or four times more than this) I decided to give it a try and It worked just fine. If you don't need precision, and speed, for the price I probably reccomend you to buy one or two and see by yourself how they work, the worst case scenario is that you expend a very few dollars in something that you can't use now but surely you will find something fun to do with them in the future.

I get them in a local store (I'm outside US) but this model is popular on ebay and RC online stores.


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