High Pressure RP backflow Device

[Kuhuh]

I have a situation where I need a Reduce Pressure Principal Backflow Prevention Assembly to meet a maximum operating pressure of 235 psi. The agency standards require a RP not a double check. The problem is most of the common manufacturers all have told me no one makes one rated for that high of pressure. They all top out at 175 psi operating pressure. The situation I have does not allow for a pressure reducing valve. Any one run into this problem before?

 

[PEDARRIN2]

If this is for a domestic water system (potable), there is a maximum pressure for fixtures of ~80 psig.

Why can you not use pressure reducing valve? If the higher pressure is a requirement, I would recommend using a pressure reducing valve upstream of the backflow to reduce the pressure, then use a booster pump downstream to bring the pressure back up. Make sure the fittings/parts are rated for the higher pressure.

 

[Kuhuh]

I have attached a simple P&ID diagram to explain why I can't use a PRV. I agree with your logic but won't work for my application.

 

[PEDARRIN2]

Put the PRV upstream of the RPZ to lower it to ~150 psig. Depending on flow, you would have ~13 psig loss across the RPZ. Add a booster pump downstream to bring the pressure up to the 200 psig required.

If that doesn't work, then you have to have a tank with an air gap to protect your source and have a booster pump to bring it back up to pressure.

 

[coloeng]

What is the source of supply for the pump you are showing on your diagram? If the source is pressurized, could you split to your two downstream uses, install necessary bfp and then boost to the pressure you need for each individual use. This would require two pumps, but because you are boosting the one to a lower pressure than the other, you may save energy costs on operation of the pumps. This would also eliminate the need for the PRV on the lower pressure use.

If the source is not pressurized, boost the initial pressure to your lower pressure needs and then install another booster pump after the BFP for the higher pressure needs.

You don't really give enough details for us to know your exact circumstances, so I'm just throwing it out there and seeing if it will stick.

 

[bimr]

What flow capacity are you working with. Why do you need such a high capacity on the non-domestic water line. What is this application.

 

[Kuhuh]

800 gpm. I have to have the higher pressure in order to pump into an existing pipeline flow direction #1. The water source is non-domestic water as well. Putting in another pump is practically uneconomical.

 

[PEDARRIN2]

If the water source is non domestic and you are protecting a non domestic, why is the RPZ required?

Why not redundant check valves?

 

[Kuhuh]

The system is for an interconnect between two agencies. The pump is pumping non-domestic well water from agency "A". The recycled water is sourced from another agency agency "B". Agency "B" is requiring an approved certified RP device in order to contain agency "B" contaminants from the recycled water entering. The thought is, if pump is turned off the recycled water can flow reverse through flow direction 2 and into whatever that pipe leads to which is owned by Agency "A". Agency "B" is trying to protect them selves from any potential cross contaminant issues.

 

[PEDARRIN2]

Your system is exceeding the pressure limits of the RPZ - so, whether economical or not, you either have to reduce the pressure so the RPZ works and then repressurize it downstream or you have to go to the next level of protection, which is an air gap, which will require a storage tank, level controls and a pump.

Another thought is to have an actuated valve so when the pump turns off, the valve closes and there is no backflow. You could add a check valve in there as well.