Hyd. Calcs with Pres. Rest. Valve

[FireSprinkler]

I have a standpipe system in a high-rise building and am using pressure restricting valves (Cla-val #90-21). Any thoughts on the 'best' way to do the hydraulic calculations with the pressure restricting valves? Could I simply calc back top the valve itself and plug in 1000gpm (flow required for my standpipes) at a given pressure, or do I go back to the pump but figure the valve in somehow?

Does anyone have any experience with this sort of arrangement?

 

[gouveia]

I have done this a couple of different ways:

1. As you suggested, simply calc it back to the outlet of the PRV. Then insert the flow demand on a second calc on in the inlet of the PRV back to the pump/city supply.

2. Call the PRV a fixed pressure loss (i.e. a backflow preventor). This allows you have a single calculation and possibly see what is happening a little clearer.

One of the concerns I have had in the past is that the pressure drop across a PRV is not fixed. The valve is not perfect. Therefore you need to verify with the manufacturer's pressure charts. You also need to maintain a minimum differential pressure across the PRV.

Hope these few random thoughts help,
Regards, Mark

 

[TravisMack]

Are you trying to calculate the sprinkler system coming off the standpipe, or the standpipe system itself.

 

[FireSprinkler]

mfpd:
Both. Initially the standpipes but later the systems that will come off the combined standpipes.

(I did not get the notification email for this response, if site manegment is listning...)

 

[TravisMack]

Ok...I didn't check into the Cla val on the 1st reply. I was thinking a 2½" pressure reducing valve for the sprinkler system control valve....

- When calculating a system with the pump and relief valve, I take the calc all the way back to the pump. However, I always check the pressures at each node to verify that the required pressure does not exceed 175 PSI, or whatever the valve is rated at...

- Since most of the fittings at the pump and standpipe can readily be obtained at 300# with minimal incurred additional cost, why not install the 2½" pressure reducing control valves at each floor, and just use Sch 10 pipe and grooved fittings with welded outlets for the standpipes...that way, you meet all of the requirements of NFPA 20. Check out Potter Roemer Valve 4036...

I hope this helps!