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Cliff Dredge
November 28, 2016, 10:10 PM
Hi,

Have a PRV that is normally shut with a reflux bypass to fill a res. The downstream pressure of the PRV is normally greater than the setting and it stays shut. Although at times when the network is configured or when breaks occur the downstream PRV pressure will drop below the set point, causing the PRV to open and maintain it's set point pressure.

Can't seem to model this, couldn't think of any logic controls either. Any ideas?

Thanks,

Cliff Dredge.

Patrick Moore
November 29, 2016, 05:29 PM
Cliff the PRV will automatically close if the downstream pressure is higher than the setting and has a built in check valve to eliminate reverse flow. If you set it up as a standard PRV it will automatically maintain the downstream setpoint or close when the downstream pressure is above the setpoint.

You should not need to write any controls, just put it in as a standard PRV.

From the image it sounds a bit different, but its difficult to follow what your requirements are.

IF you need to allow the PRV to provide reverse flow then add a bypass line with a check valve from the downstream side of the PRV to the suction side. That line will only open if the suction head of the PRV falls below the downstream of the PRV. IF you want to have control on the reverse flow CV (you can't control a CV pipe) then add a short pipe downstream of the CV and put your controls on that pipe (open when pressure below 13m and closed when pressure is at or above 13 m. The CV will then allow flow as needed based on the heads when the downstream pipe is open.

Hopefully this at least gives you ideas to try. Reply back to this thread if you need further assistance or if I misunderstood your control scheme.

Patrick


Hi,

Have a PRV that is normally shut with a reflux bypass to fill a res. The downstream pressure of the PRV is normally greater than the setting and it stays shut. Although at times when the network is configured or when breaks occur the downstream PRV pressure will drop below the set point, causing the PRV to open and maintain it's set point pressure.

Can't seem to model this, couldn't think of any logic controls either. Any ideas?

Thanks,

Cliff Dredge.

Cliff Dredge
December 1, 2016, 07:25 PM
Hi Patrick,

Thanks for your reply.

Yes there is a bypass for reverse flow. I had a pump running that was playing havoc. I used the PRV initial status setting control and it's spot on.

Thanks!

Patrick Moore
December 2, 2016, 08:46 AM
Cliff,

Glad to hear that was enough to get you going! Best to you in your future modeling efforts!

Patrick