Motorized valve duty cycle?

[Kabir]

I am connecting a Motorized control valve to a PLC5 with a duty cycle of 50%ED.

Now duty cycle as I know it to be is the ratio of time on and time off in this case 50/50. What about minimum ON or maximum ON time or what cycle time are they referencing the 50% to?

 

[TheStarr]

You did not provide a part#/manufacturer for the valve. That is probably why your question went unanswered.

But, I will assume that it is not a proportional control valve. Just a standard open/closed type valve.

The 50% duty cycle means, for example, that if the valve takes 3 sec to close, then you need to wait 3 seconds before re-opening.

If it took 10 seconds to close, you need to wait 10 seconds before re-opening. Got the idea?

They don't list an actual time because they know approximately how long the valve is going to take to cycle under normal conditions.

 

[Roy Matson]

What it means is it can motor for 50% of the time, for example over a 1 minute period it would be moving for 30 seconds and idle for 30 seconds whereas expecting to continuiously open/close for an hour then wait an hour would likely burn it out.

 

[bernie_carlton]

Roy - solely from the information given by Kabir how do you come up with a figure that 1 hour is too long? The issue that Kabir has is that he cannot find a max time listed. Where did you get the one you stated?

Kabir - determine, if you can, the maximum amount of time it takes to complete one full cycle of the motorized control valve. That should be used as your 'max time'.

 

[mellis]

I'm sure that as the valves get bigger, waiting in between each operation of the valve becomes more critical.

However, this is some data based on past experience with valves in the 2-4 inch range.

I once did some work in a plant that had lots of motorized valves. I was on a recontrol project. During the early phases, I'd noticed that some bright person had rewired two of the valves so that the limit switches were no longer in series with the motor coils. They were wired to PLC inputs only. Obviously, these valves had slightly different logic.

Later on I replaced the code for those two valves, I'd been meaning to get them rewired at the same time so the code was written for standard valves, but I forgot. So what happens? These valves just keep rotating and never stop. They weren't critical and the only person that noticed it, didn't think to mention it to me so they went until they failed. Took a couple days for the first one to melt down. Once the maintenance tech noticed it, he went looking for the other one (he knew there were 2 wired different) and found it still going but extremely hot. He replaced both actuators and all was well.

 

[Kabir]

I must say sorry for the lack of information within my post but it was really because of a lack of information about the valve itself.

This is what else I can supply you guys with 60mm Travel at 0.44mm/sec.
With that I can work out my maximum time the valve motor should be on for complete travel however my problem is more on the other side of things.
i.e for tight control what is the normal safe minimum time I could pulse the valve in a particular direction for?

 

[mellis]

Seems like your valve is for proportional control. The ones I was talking about were on/off types.

Manufacturer and model number on the motor operator would be helpful.