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Cycling Too Fast. Help


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#1 idonotknow

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Posted 05 May 2012 - 10:52 PM

some info.

2 119 gallon tanks
goulds variable frequency drive
12 hp motor
230 gallon a minute
commercial business/ laundromat

I just switched to vfd system. was told i only need 1 119 gallon pressure tank (psi of tank at 48) but i installed 2 just incase if one went bad. I had 7 before the new system. the psi at the switch is set at 55 to 62. when i installed the system i noticed my pump was running way too much. when there was medium demand i would notice the psi at the switch go from 55 to 61 then go back down and go up and then go back down then finally set at 62 and it would finally stop. (then turn on again) is this normal? i am thinking this is bad for my pump. Do i need more tanks because everyone i talked to said 1 tank would be good enough but then i dont understand the short cycling. do i need to decrease pressure? increase?

#2 marke

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Posted 06 May 2012 - 04:57 AM

Hello idonotknow

Welcome to the forum.

It sounds like you are using a pressure switch rather than a pressure transducer.
If you use a pressure transducer to control the pressure, I would expect that you would not have a problem.

You would need to set the drive up to work with the PID with the presure transducer connected to the feedback input and a set point set on the reference.
We do this very often without problems.

Best regards,
Mark.

#3 idonotknow

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Posted 07 May 2012 - 03:09 PM

thanks for the feedback mark.. but i have no idea what youre talking about. lol. is there any was to make it work without that? maybe more tanks? lower pressure?

#4 marke

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Posted 07 May 2012 - 10:53 PM

If you are using a pressure switch to start and stop the VFD, there is no point in using the VFD.
The advantage of the VFD is that you are able to control the speed of the motor, but to do that for your application, you need some intelligence to tell the VFD what speed to run.
Most modern VFDs include a PID control system that can be set up. In your case, you would use a pressure transducer which provides an output proportional to the measured pressure. The PID control system compares the measured pressure against a set point presssure and tells the VFD to speed up if the pressure is low, or slow down if the pressure is high. This way, it keeps the motor and compresor running all the time with the speed following the demand.

It appears that you are not familiar with setting up VFDs in this type of operation. I recommend that you contact someone locally who would be3 able to set it up for you.

Best regards,
Mark




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