Solenoid coil drop out speed

[tgcoakley]

I have a 120 volt ac coil on a 2" water valve that I would like to convert to slow operating to prevent water hammer. Can I accomplish this with a capacitor and a resistor or will this just create a delay in operating circuit with the same operating speed?

 

[Skogsgurra]

A capacitor will most likely not work in an AC delay circuit (it _could_ work, but then as part of a resonance circuit and not as a classic delay element).

Even if you convert to a DC valve, you will probably not get anything but a delayed off. The magnetics will keep the valve open until it can't hold it any more. And the plunge moves just about as fast regardless of how you reach that point - be it fast AC off or slow DC off. You need a valve that closes slowly to avoid water hammer.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[tgcoakley]

Thank you. Are you saying that the circuit would be like a tank circuit? And I guess when the delay circuit lets the threshold voltage down to the value where the spring overpowers the coil, the speed of close would be the same.

 

[Skogsgurra]

Yes. You got it!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

There are plenty motorised valves out there for the commercial heating market which will give you the characteristic you want for a reasonable price. Slow on-off just isn't a solenoid valve feature: most valves of this size use the solenoid to control a pilot line to a diaphragm, and the soft parts of these valves aren't designed for throttling duty (i.e. operation in a part-open state).

You might want to ask the question in the HVAC forum, or maybe the Valve Engineering forum. The valve people are usually more biased toward industrial process control, so my bet is with the HVAC guys: forum403.

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[tgcoakley]

Thank you all for you input!!! The solenoid yalve was chosen to maintain a tank level in our ozone laundry systems. As a commercial washer (one of 4) demands treated water, it is pumped out of the treated water tank (refilled by city water via the solenoid valve). We considered a motorized valve, but the closing time of 10 to 16 seconds causes the tank to overflow before the motarized valve can shut.also the high number of cycles tends to overheat the operator and it might stick in mid-position asit cools down.

I bit the bullet and purchased the slow closing (2500 msec) solenoid valves, rather than trying to do product development at our customer's location. The high cost and low availability of slow closing solenoid valves prompted me to explore another way.

 

[itsmoked]

Your other option would have been to put in a surge eliminator. A little tank with a diaphragm in it.

I built one for my bathroom sink. I have a $700 IR no hands bathroom fixture and it shuts off so fast all the pipes in the house rattle and sleeping people get woken up.(ridiculous!)

I built a surge tank out of PVC fittings and put in a smaller orifice to create an RC. Works fine.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[OperaHouse]

In many solenoid operated valves, the solemoid omly operates a small pilot that operates the larger valve. I doubt that slowing down the solenoid would do anything. You are stuck with finding some mechanical ball valve or a snubber for the pipe.

 

[ScottyUK]

Hi Operahouse,

That almost sounds like "Slow on-off just isn't a solenoid valve feature: most valves of this size use the solenoid to control a pilot line to a diaphragm" doesn't it!

tgcoakley,

For our collective benefit, where did you find slow-acting solenoid valves? Do you have a manufacturer and part number? Good to know you got things sorted out.

 

[lighterup]

Keith has the most cost-effective solution to the problem, a surge eliminator. I have seen this implemented by installing a parallel vertical closed-end pipe stub filled with air, which unlike water is compressible. The air acts as a shock absorber, and dampens the pressure wave created by the fast acting solenoid valve. The stub should be placed as close as practical to the offending valve, and care should be taken that it does not fill with water prior to closing the end. Also, the larger the diameter of the pipe stub the better.

 

[tgcoakley]

Scotty,

Burkert German) makes a solenoid valve that is slow closing. It and the ASCO Vave 8221 series are somewhat expensive, but they work without surge eliminators, which in our 2" 80 psig existing laundry room application might require some trial and error to get it right.

 

[jraef]

If you are using a motor operated pump to do this, you could simply put in a soft starter or VFD and slow the pump down (soft stop).

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[danw2]

The statement on the ASCO spec sheet for the 8221 series "Slow Closing" 2 way solenoid valves says, "Snubber slows disc closing speed to protect system against
water hammer damage more effectively than other techniques."

http://www.lesman.com/unleashd/catalog/valves/valves_8221.html

This vendor indicates either stock of 3-5 day availability of several models:

http://www.lesman.com/acatalog/Online_Catalog_2_Way_Slow_Closing_Valves_186.html

Dan

 

[ScottyUK]

They look like an interesting alternative to motorised zone valves. More expensive, but I suspect far more reliable too.

Thanks tgcoakley and Danw2.


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