Seeking plumbers advice. Is a pressure relief valve needed?

[Reedmaster16]

I finished putting together an auto refill system for the sump of my new 800 gallon aquarium and had a couple questions.
First let me just breakdown what I am trying to do.

I teed off the hot and cold water lines and soldered a ball valve on each.

From there I added a check valve on both the hot and cold lines and a thermostatic mixing valve downstream to regulate the temperature of the water.

After the mixing valve I placed a pressure reducing valve (set to 50psi) that goes into a whole house 20" sediment and carbon filter.

I then reduced the line down to 1/4" high pressure poly tubing that runs through two additional granular activated carbon filters. The line then goes into a float valve in the sump that opens when the water level drops to a certain point. (An automated refill system for water changes)

I began it testing last night and everything worked flawlessly when the float valve was open adding water to the sump. The water flow rate is around .5-1gph.

When the water level rose enough to close the float valve for an extended period of time is where an issue popped up. After about an hour or two minor drip leaks began developing at the hot and cold inlets of the thermostatic mixing valve from what I believe to be an excessive amount of pressure. I shut down the hot and cold supplies and vented the excess pressure by pressing the air purge button on the top of the 20" whole house filter housing.

The float valve will only open when the water level drops from evaporation and when I perform bi weekly water changes. So it would open briefly for an estimated 2 times per day to replace evaporated water and 2 times per week for around 2 hours to refill after I do the water changes.

Is there a major flaw in the plumbing layout anyone can point out to me?

Would a pressure relief valve be a potential solution to the excess pressure build up when the float valve is closed? Other suggestions options?

Any help would be greatly appreciated.

Thanks,
Reed

 

[Reedmaster16]

Bump for any helpful suggestions/advice

 

[kendragon]

When you say minor drips at the mixing valve, is that internal or external? I mean is it leaking out of the coupling or pipe? Perhap the pressure regulator should have been before the mixer or do you have one already somewhere before the heater?.
My experience with household water pressure is when the heater kicks in, the house pressure rises. Put a pressure gage on a cold water hose bibb. Watch it increase when the heater starts boiling.

 

[kendragon]

Also using joint compound on the brass nuts may allow you to torque them a little tighter to compress the flat o-ring a bit more.
50 gallons of hot water expands as much as 2 gallons, they remedy this with an expansion tank. Google it.

 

[Reedmaster16]

Thanks alot for replying Ken, always very much appreciated.

The pipe expansion from the hot water was one of the primary things that concerned me. I would have gone with just the cold water line for the refill but the tank was close enough to the hot water tanks for the heat loss to be minimal. As you mentioned a pressure regulator on both the hot and cold lines upstream from the mixing valve appeared to be the ideal setup but I was hoping the pressure would be low enough to not cause any problems/damage and I could get away with one PRV. The mixing valve is rated up to 150 psi.


I was informed by a plumber yesterday that the system ahead of the mixing valve should never be able to generate enough pressure to cause the leaks. In addition, the pressure after the regulator has nothing to do with the pressure ahead of it. If the regulator is working properly, there is no "excessive buildup" when the float valve is closed.


I took apart the mixing valve last night and cleaned the o rings off and reapplied silicone based lubricant. I was able to tighten the brass nut a little farther on than before. Tested it for the refill and worked great again with no leaks. I only left the hot and cold valves open for an hour after the float valve closed to observe and there were no leaks.


It looks like it could have been the o ring was not compressed enough to handle the incoming water pressure with the float closed. Or at least this is what im hoping the issue was haha. I am going to keep testing this weekend into next week with longer intervals of the hot/cold valves open with the float valve closed to see if any leaks develop. Worst case scenario I will have to buy another PRV and have one on the hot water line and one on the cold water line as well before the mixing valve.

I will post results for future reference for anyone who may try something similar.