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Which Solenoid is better and why?

2Biz

2Biz

Thread Killer!
I am comparing the difference between a Pilot Operated Piston Solenoid and a Pilot Operated Diaphragm Solenoid. I’m mainly comparing the differences between a Dema 414P and a Dema 474P, both are ½” solenoids. The 414P has a .438 orifice and the 474P has a .562 orifice. Aside from orifice size and Cv rating, why would you select one over the other? There is less than $5.00 difference in the two.
 
I bought a couple of the 474P diaphragm type about a year ago. The first one failed "full open" the next day. The other one lasted about a month and did the same thing. Needless to say, I went back to the 414P.
 
Piston valves require slightly higher inlet pressure to maintain closed position. This means they don’t always close in gravity feed installations.

Diaphragm valves tend to open and close more slowly than piston valves and are more likely to suffer from failure due to chemical degradation of the diaphragm.

Diaphragm valves are recommended for unfiltered fluid applications but tend to fail open due to contamination/clogging of the diaphragm bleed hole. Also, reduced output is caused by contamination above the diaphragm...preventing full opening of the valve.
 
Thanks CB80 and I.B.,

I.B., What was your application when the 474P failed?

I had a 414P on my weep system. It failed closed (Caused a freeze up) and I replaced it with an Asco Diaphragm type valve. The Asco has been flawless. I opened the 414P and found a lot of Calcium/Lime buildup. I have no idea how long it was in service....

I'm trying to decide which valve would be the best for direct/regulated city pressure to my pumps. I know Randy uses the 414P and doesn't have any problems. I'm trying to make the most educated decision based on the specs/service life of the valves. Dema does not list service life on their valves. Asco's diaphragm valves have a 10,000,000 service life for comparison. I may like the idea of a slower acting valve to minimize water hammer, but could there be vacuum issues with the valve when the pump kicks on at the same time? Could this cause a diaphragm valve to fail closed? I don't have to worry about chemical degradation since its a water only application. Thanks!
 
Mine was used to fill the pre-soak water holding tank on a Mark VII auto. It received soft water at city pressure and filled the tank with water only, no chemical. The chemicals are injected downstream, the valve comes in contact with nothing but clear water.
 
Dema USED to be the best solenoid - I've seen 40 year old ones on pump stands that have never been touched and work perfectly. Our equipment was built with 412P, and all of them failed within a few years, some wouldn't open fully and some wouldn't close. There was nothing visually wrong with any of them. I've also had brand-new O412P solenoids on weep systems fail to open or close the first time they were called to cycle.

The Vector has ASCO RedHat solenoids on the low-pressure manifold, and I've replaced many of them because the brass seat eroded. I use Dema 473P or 474P on everything and have never had one fail to open. Out of a dozen in service I've had a couple not close fully, which was fixed with a diaphragm kit.
 
Why is it solenoids work better for some and not others? How can that be? I have to get (8) of these 1/2" solenoids and would like to get the right/best ones first time out of the gate. Enie, Meanie, Minie, Moe!

Mep, Most of the 1/8" Dema's on my pump stand are the original ones installed. They were installed about 1985....But they are the direct acting kind. They don't have pistons or diaphragms to go bad or fail....
 
Those were made back when Dema solenoids were still made well, and there's only one moving part: the plunger. The others have close-tolerance parts, and more of them, so of course even the slightest problem causes a failure.
 
Of all my solenoids, the Rainbird's are by far the most reliable. And, they're always in stock at Home Depot!
Too bad their specs indicate Max temp of 110F! :)
 
Rainbird's....Never heard of them! A google search indicates they are for irrigation and are all plastic? And they are your most reliable?
 
Oh...I forgot you're not in "irrigation country". Our landscaping would not survive with our sprinkler systems.
Yeah...they're extremely reliable. I can't remember repairing more than 4 out of the 60some Rainbirds I've owned. And, all they needed were diaphragms. At one property I've owned for 20 years, I can't even find 7 of them...they're buried somewhere in the backyard??? Fortunately, they just keep on working.
 
We’ve used the DEMA 0414P solenoid valves for over 30 years, in 30 plus years I think I’ve replaced maybe 3 of them. We don’t try to rebuild them, we keep one spare and just replace them when they go bad, when they go bad they’ll leak by. All solenoid valves have their own application, so saying that all DEMA and ASCO solenoid valves are not good is not a correct statement, there were probably used in the wrong application.

2BIZ here's a link to Rainbird http://store.rainbird.com/default.aspx?gclid=CPv5i6jU0LoCFeh0QgodNE8AIw
 
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