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Experience Answer About IP 4..20 valves behavior.

I may have asked this once before. We've been living with it as is because it seems to work but is not acting as it should.

The scenario:

Curing ovens that use steam heat exchangers for the radiant heat employ a 4..20 ma output controller to drive a 4..20 IP valve which outputs 0..20 PSI to a pneumatic valve which gates the steam.

The IP controlling actuator is a simple unit that employs a ZERO set point (mechanical)and a spand (electrical), its nothing more than a DC magnet with spring tension to meter the air to the output which follows the 4..20 ma signal.

The problem is when the output is reaching 10 Lbs or more, the IP solenoid starts to pulse/chatter on the output. We use these units else where with out this problem..

Q. could it be that there is a long run of air line from the output of the IP to the input of the steam actuator valve? This is the only thing I can contribute to the problem?

P.S. The signal from the controller is steady btw.

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Jamie
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It sounds as though the resonance of the air line is too close to that of the mass and spring of the solenoid valve. Similar things happen to stepper motors. Shortening the line to raise the resonance, or putting a local air tank near the solenoid valve to lower it should help.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

yes, that sounds like the problem.

The line is that 3/8 air hose (not pipe), its a temp install for the time being how ever, it's about 50 feet between the gate valve and IP. Some times if I disrupt the air and let it resume, the oscillation stops. it's about 2 Hz oscillation.

Mechanical engineering is not my #1 area how ever, lately, it seems that i've had to dig into my old engineer books and blow the dust off them. I did find a section in there on oscillation of air movement. Lots of formulas to work with.. Most of them practical, some a little off the wall but still ok. Ok, thanks very much for your services. check is in the mail :)

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

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