Motorised Proportional Valve Control

[johnf]

I want to maintain a constant pressure of 5.3bar in a compressed air ring main by exhausting air through a silencer using a 1inch ported Valpes motorised proportional valve. The air demand varies from high to low throughout the day so valve position will continually change. There's a 0-10bar 4-20mA pressure transmitter in the air line which is used to measure and record pressure.
So far so good. Now the bad bit. The only tool left in my toy box is an SMC/Mitsi Alpha 10 i/o controller.
How can I use the output from the pressure transmitter to control the input to the motorised valve?
Thanks for your help!

 

[leitmotif]

I want to maintain a constant pressure of 5.3bar in a compressed air ring main by exhausting air through a silencer using a 1inch ported Valpes motorised proportional valve. The air demand varies from high to low throughout the day so valve position will continually change. There's a 0-10bar 4-20mA pressure transmitter in the air line which is used to measure and record pressure.
So far so good. Now the bad bit. The only tool left in my toy box is an SMC/Mitsi Alpha 10 i/o controller.
How can I use the output from the pressure transmitter to control the input to the motorised valve?
Thanks for your help!

John

Sounds like a plant air system. 5.3 bar is about 90 psi. How much volume are you talking about here?
Could be done with a system like you propose
BUT
assuming this is plant air with a large flow ie 20 cfm or more.
why compress the air only to dump back to atmosphere?
Compressed air is most expensive utility in a plant.
think I would control at the compressor to ensure delivery no more than 90 plus allowance for line pressure drop.

Dan Bentler

 

[TConnolly]

Sounds incredibly wasteful. What you are proposing will be an energy hog. Like Dan said, compressed air is the most expensive utility in the plant, and not by just a little bit but by a factor of 8 times or more. If you vent back to atmosphere then your compressor will run fully loaded all the time.

Use a mechanical air regulator between the ring and the air compressor trunk line. It will be more stable and provide better response and it is set and forget. On the compressor side of the trunk add a surge tank so that the compressor is not constantly loading/unlaoding or starting/stopping.

Since being green is vogue, especially in the compressed air business, your compressed air equipment vendor will probably be more than happy to discuss energy efficient options with you, and given the cost of compressing air, the options are very easy on the pocket book.

 

[johnf]

Not sure what happened to my earlier posted reply.
Yes, I agree it's energy wasted but I'm comparing the performance of two spin on separators fitted to two 90scfm screw compressors and need as many hours on full load as I can in the shortest time to complete my test program. It's less wasteful than the other option I have of dumping all the air 24/7 and using a third compressor for shop air 6am-10pm.
Back to the task in hand. It's been suggested I use an analogue expander on the SMC controller and use this output to control the valve. Does this sound feasible?
John

 

[leitmotif]

Not sure what happened to my earlier posted reply.
Yes, I agree it's energy wasted but I'm comparing the performance of two spin on separators fitted to two 90scfm screw compressors and need as many hours on full load as I can in the shortest time to complete my test program. It's less wasteful than the other option I have of dumping all the air 24/7 and using a third compressor for shop air 6am-10pm.
Back to the task in hand. It's been suggested I use an analogue expander on the SMC controller and use this output to control the valve. Does this sound feasible?
John

John I assume you mean water air separator. We had these screw on type (or cartridge if you want to call it that) on a 60 (??) HP screw dont know flow. Had factory fitted DP indication - never went into red zone. So I guess they worked OK.

Myself I would put a Magnehelic or similar DP gage across teh filter and measure pressure drop.

The loss in power across a filter due to PD is much less maybe than the lost money spent on damaged components due to water in air.

The other think I would consider is how much water is still in air after the filters.

What are your test criteria ie what aspects of perfomance are you testing for?

Dan Bentler

 

[johnf]

Dan,
It's the air/oil spin-on separator inside the compressor we're testing. We're comparing the rate of DP and oil carryover increase over time with separators A & B using a standard air intake filter.
John

 

[leitmotif]

Aah THAT separator.
So why are you doing this
--- to reduce carryover
--- reduce DP on separator?
Both ?? Now that would be nice.
Would like to hear more about this

Dan