Deadend waterline

[SMIAH]

A water pipe will be installed with a check valve so that the flow from network #1 can come in support to network #2 if the pressure drops (e.g fire protection).

Under normal conditions, the static pressure in network 1 = 68 PSI and the static pressure in network 2 = 129 PSI.
When network 2 drops below 68 PSI (say a little under) the check valve will open and flow from network 1 will come in support to network 2.

I'm trying to find a way to maintain a minimum flow through the pipe to avoid having a dead-end waterline.
A way to maintain a minimum flow so that this volume of water (5 cubic meter = 160 m @ 200 mm) is not stagnant for more than 1-2 days.

The head differential is quite high though (129 - 68 = 61 PSI) and I don't know any diameter/length/roughness/Head-loss combination that can keep a low flow (say a drawdown in 24 hours).
Do you have any ideas of what device (purge) or simple solution that can be applied to this problem?

Thanks

 

[SMIAH]

A sketch

 

[cvg]

why not a small diameter bypass line with an orifice to limit the flow? you only need about 1 gpm, so the size would be quite small.

 

[SMIAH]

That's my point. The size has to be really small, isn't? I don't want more than 1 GPM and the head (61 PSI) is high.
I think a 1/4'' is too much.

 

[LittleInch]

What about drilling a small hole in your nrv flapper or whatever it made of. Start with 3mm and do an orifice calculation to get your small flow. The only issue with v low flow is that it might not flush the entire cross section and laminar flow probably results.

I assume your water is very clean otherwise any flow restriction will quickly block up.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

You most likely will put the check valve into a vault. If you have electrical power at the vault, you can use a timer and a solenoid operated check valve (ClaVal) to periodically cycle the check valve.

 

[SMIAH]

(it's clean water)

The check valve has to open in the opposite direction. It can't open in both side (?)

 

[77JQX]

We use these for exactly what you're facing.

http://www.okcc.com/PDF/Restriction Orifice Union pg.29.pdf

 

[SMIAH]

We're thinking using a pressure reducer with a valve and a flow-meter as a bypass on the check-valve.
So we can adjust it to approx. 1 GPM.

Thanks for the reducer. I'll keep this info.