Yes I agree with the addition of the expansion tank and the check valve in those locations shown on your diagram.
I'm not so sure about your circulator pressurizing the cold water feed. A circulator for that application typically wouldn't be capable of producing a pressure greater than the domestic water pressure. It's only has enough pressure capabilities to overcome the friction loss when circulating.
My name is Diehard for a reason. It bothers me that I can't see the actual cold water connection(shown as a tee in your sketch) to either the high or the low pressure systems.
Could you take a picture of those 2 tees where the domestic CW is connected?
I'm not sure what else it could be. Do you think thermal expansion alone could cause it to bury the needle on a new gauge? Picture of the gauge is just so you can see what it is. It's not the most expensive on the market but read 50 psi when I first installed it with the prv so I'm confident its correct.
Now that we have established a check and expantion tank are indeed called for in this system, what about sizes? It's a half inch line so I assume a .500 spring check would be sufficient in combination with the expansion tank. Should I install a 2 gallon tank or try to get a mini? Inflate to static pressure of the high pressure system correct?
As I suspected, that low pressure PRV behind the boiler is connected to the domestic hot water system, which is suppose to be the high pressure. Your sketch shows it connected to the Heating system. Don't you agree or am I missing something?
Where is that High pressure PRV tee'd into the system. You show it in your sketch as located between the storage tank and the boiler, which is also feeding the Domestic hot water system.
Somethings not right.
I'll have to take a fresh look at it in the morning.
I think you are confusing the direction of flow. If you look at the upper left hand corner of my sketch the prv is a little bit cut off. That is the high pressure prv reducing city supplied water pressure.
The other prv you are referring to is flowing in the direction of the heating system. I know it works because just today I shut down and isolated the boiler. Depressurized and drained the heating side and installed a new 30 psi pressure relief valve. When I recharged the system I toggled the lever on the low pressure prv to fill and I heard it seat while watching the pressure on the boiler come up and stop.
The prv in the beginning of the system does have an integrated bypass. In the event thermal expansion causes the system to rise above the city supplied 125 or so psi it will flow backwards.
The prv above the boiler does not have this feature. I think I will install a backflow preventer as well. Upstream of the low pressure prv and down stream of where it tees into the cold water.
Yes I give in!
I was basing my assumption of the flow direction on the fact that it was connected to the domestic HW circulating loop.
I neglected the CW drop from above.
In response to earlier questions...
Thermal expansion could definitely cause pressure to go exceptionally high when it has no where to expand to. Just depends on the amount of rise in temperature.
Why a spring check as opposed to a swing check?
The size of the expansion tanks are typically based on size of storage tank, the typical maximum pressure and the maximum temperature.
If you look up a tank type water heater, it will show you the recommended sizes of expansion tanks. But be cautioned as their chart for residual applications is likely based on 120 degrees, while your system would fall under commercial since you are using the higher boiler water temperatures.
For example if your tank was 50 gallons, max temp of 140 degrees, and pressure of about 50 to 60 psi, they would recommend a 4.5 gallon minimum.
Spring because I intend to install it on a vertical pipe. It also closes faster, so you get less of the water hammer effect. I intend to do this install fairly soon. I priced everything out. Shouldn't cost more than 150 or so. I'm going to change out a few valves that are crusty and no longer functioning. I'll post pics of the final product and whether or not it solved my problem. Thanks for all the time you spent responding to this post!
I FINALLY got the time to install the check valve and expansion tank. It took longer than expected and I think I deviated from my original plan. I didn't write down my plan but the list of fittings I bought a few weeks ago didn't match up to what I used. Anyways the sweat joints are far from pretty but all 920 of them are holding. Fingers crossed!!
Now what you all came here for... the water hammer is gone!! I'm getting a steady static pressure of 60 PSI and a drop of about 7 PSI when a fixture calls for water. Thanks for all your help diehard.
On another note, what do you prefer for torch fuel? Propane or map gas? I like the map gas but I think I overshoot the ideal temp to flow the tin.
Hope you all are safe and healthy in these crazy times.
I have not sweated any fittings in a while now.
But when I was doing more of it, I usually got along fine with regular propane.
You need a decent torch, some of them don’t concentrate tightly, and they somehow are just weak output, like they are not pulling in enough combustion air.
I did resort to Mapp gas a few times, when I was soldering big heavy brass fittings that were hard to heat up.
Glad to hear it!
All's well that ends well.
All my soldering has been limited to propane, as I am not a plumber. I was a plumbers helper(with my father and brother) part time for many years when young but my mother didn't want me to come home dirty all the time, so I ended up dabbling in plumbing engineering, for an environmental engineering firm.