That second valve would make it a closed system and keep your well tank from absorbing that pressure.
Expansion tank pressure switch.
Code requires an expansion tank only if the system is closed this absorbs excess pressure as the water heats.
If you do have another check valve then you would need an additional expansion tank also.
A bladder expansion tank is a system which is used for heating and cooling purposes by absorbing the expansion force.
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Most expansion tanks come pressurized to 12 40 psi but before you install the tank you have to match the system pressure.
The pressure switch monitors the pressure in the tank.
During this draining watch and listen to the water.
Close off all plumbing fixtures that are using water in the building.
Start by removing the protective cover from the air valve on the tank.
It informs the well pump when to turn on and when to turn off based on the rise and fall of the pressure within the tank.
Use a tire gauge to check the pressure.
Open one or more plumbing fixtures to drain the water pressure tank.
Turn on the water pump and let the system run until the water pump cuts off.
Here is the procedure.
Start by removing the protective cover from the air valve on the tank.
Use a bicycle pump or compressor to fill the tank to match the system pressure you noted earlier.
Most households are set up to run with a pressure switch that turns the pump on at 30 pounds of pressure and turn the pump off at 50 pounds of pressure.
Most expansion tanks come pressurized to 12 40 psi but before you install the tank you have to match the system pressure.
Use a tire gauge to check the pressure.