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Discussion Starter #1
Motorized valve nothing special just a geared motor and 2 micro-switches caused me grief today. (less than a few weeks old)

Valve fails to make the limits but when i open the actuator the alarm clears. Watch it cycle a few times and can not repeat the problem.
Called back same problem a hour later.
This time i check the plc side and the valve is not indicating closed but the valve is physically closed.

Open the actuator and the alarm clears again.
So its going to be one of them days. 20 cycles later with the cover removed it finally failed and the meter showed the micro-switch n/c opened and the n/o did not make. Accidentally tapped the switch with the meter prob and heard the tiny click and now the the n/o is closed.
Never seen this happen before so i removed the switch and was unable to replicate the problem in my hand. I found this interesting so i dissembled the micro switch and drilled a hole so i could see the contacts then reinstalled it. A few cycles later it failed again and the n/c had opened (motor feed) yet the spring had not caused the contacts to change (gap was tiny between the contacts). Just a tiny tap on the body of the actuator completed the state change. (no visible mechanic jam in the switch)

So now i know im not going mad so i stole a micro from a new valve and have some on order. I thought that it was impossible for a micro to do this but i guess that's what you get from thinking.
 

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Bilge Rat
motors and controls.........
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I've never seen an actual micro fail, the main problem I've seen is the cam doesn't push the plunger far enough.
 

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Had a brand new oil flow switch be bad right out of the box not too long ago, was one of those little microswitches with an arm with a roller on the end of it. I fully actuated it manually and the NO contacts wouldn't close, preventing the start of the machine.
 

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HVAC-R master tech, over 20 years playing with wires
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18 Posts
Im not bothered if it doesnt last i just want it to fail in a predictable way. Nothing worse than trying to find a glitch and having to change a $800 head to fix a 20 cent switch.
Thats good how you babysat to find out whats actually going on. There are many who would rather throw parts at it.

I have babysat many long hours in my life. Granted it sucks big time , but it usually pays off. Friend of mine just babysat a RTU for 6 hours straight before hearing a intermittant spark tripping the breaker, and he was like " Jesus Christ , FINALLY"...lol
 

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Ready Mix concrete plant electrician
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I've never seen an actual micro fail, the main problem I've seen is the cam doesn't push the plunger far enough.
I’ve seen a few fail on cement gate duty. The ash and cement powder is a pernicious substance that gets into anything and everything eventually.
 

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442A -Industrial Electrician's ticket since '93
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I find the working environment has a lot to do with microswitch failures. It doesn't take much foreign material to jam the roller arm or the mechanical plunger that switches the internal contacts.
Is changing to another style of switch practical? Any means of positioning feedback on the motorized control? This would allow you to use the micro as a redundant backup or even eliminate it.
 

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Discussion Starter #11
I find the working environment has a lot to do with microswitch failures. It doesn't take much foreign material to jam the roller arm or the mechanical plunger that switches the internal contacts.
Is changing to another style of switch practical? Any means of positioning feedback on the motorized control? This would allow you to use the micro as a redundant backup or even eliminate it.

normal these controllers do well as long as no one smashes the plastic indicator from the top.
micro.jpg


bad micro switch was the bottom one. Its a real simple design. Common is power to motor, Motor runs till it opens switch, common via N/O now goes to relay board for plc input.

Can not find the picture where i moved the bad one to the top and drilled a hole in it. It sounds anal to go to all this hassle for a simple valve controller but it's 70 miles from home base so i want to be 100% sure i have found the problem rather than thinking i had found it.
 

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Good job on the diagnosis. I have installed a bunch of those same valves. I absolutely hate adjusting the cams on that valve. To get to the set screws in some positions you have to remove parts and then the cam slips down and isn't centered with the micro switch.
 

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Chief Flunky
Field Service Engineer
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You are not going to get down to 20 cents but an inductive proximity switch is an inexpensive and nearly indestructible replacement. They can be buried in cement and keep working. Even in steel and iron plants. See IFM Efector for good ones.
 

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Discussion Starter #14
You are not going to get down to 20 cents but an inductive proximity switch is an inexpensive and nearly indestructible replacement. They can be buried in cement and keep working. Even in steel and iron plants. See IFM Efector for good ones.

We probably had 2000 Efector prox switch's onsite and i have replaced hundred of them. Outside the led seal/glue fails in sun light (dry rots) then they get wet inside and die.
Inside the plastic turns brittle and they snap really easy especially after being exposed to orange juice. (orange oil)
 

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Scada Supervisor
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Those type of switches are notorious for that. We had them on air valves and if air pressure was to low valve moved real slow the switch would not change state. We also had them in our MIG welders and the operators learned that if you released the trigger slow enough they would not change states, and the wire would continue to feed. They would power up the machine and wire would feed, we would squeeze the trigger like nominal and everything worked good. This way they would get out of work till we got there.

Cowboy
 
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