where to put the expansion tank??

shredmaster

this is the current piping illustration:

return: 3 zone valve, isolation flange with drain, circulator pump and cold water inlet
boiler: built in automatic air vent on the supply side
supply: boiler isolation + 3 branches to their zone.



If understand pumping away correctly, the circulator would be pumping toward the expansion tank if the expansion tank is right after the fill valve (position . Should I put the expansion tank before the isolation flange (position A)?? Or maybe either position would be fine.

Thanks!

Steven

HomerJSmith

Your drawing is hard for me to understand. Pumping into an EX tank is not to be done. Always pump away from an EX tank. That means that the tank should be connected to the input to the pump.

When you have a conventional hi mass boiler with very low head loss and the pump is on one side of the boiler pumping toward the distribution sys and the tank is connected to the other side of the boiler that would work. If you are pumping toward the boiler from the distribution sys. the tank should be put on the input to the pump at least 10" away from the input. The air separator should be on the outlet of the boiler toward the distribution sys ( the hottest water).

Alan (California Radiant) Forbes

Position "A" will work best. The differential pressure will be added to the outlet piping of the pump, keeping the system properly pressurized.

In position "B", the differential pressure will be subtracted from the suction side of the pump, possibly low enough to allow air to enter the system.

shredmaster

HomerJSmith said:

Your drawing is hard for me to understand. Pumping into an EX tank is not to be done. Always pump away from an EX tank. That means that the tank should be connected to the input to the pump. When you have a conventional hi mass boiler with very low head loss and the pump is on one side of the boiler pumping toward the distribution sys and the tank is connected to the other side of the boiler that would work. If you are pumping toward the boiler from the distribution sys. the tank should be put on the input to the pump at least 10" away from the input. The air separator should be on the outlet of the boiler toward the distribution sys ( the hottest water).

I have the circulator on the return side. Why does the tank need to be put at least 10” away from the circulator?

shredmaster

Alan (California Radiant) Forbes said:

Position "A" will work best. The differential pressure will be added to the outlet piping of the pump, keeping the system properly pressurized. In position "B", the differential pressure will be subtracted from the suction side of the pump, possibly low enough to allow air to enter the system.

I should definitely go with position “A” then. The boiler manual recommendations to have the expansion tank after the boiler isolation valve. 

I have a isolation flange with drain, so in position A, the expansion tank is above the boiler isolation valve. Is there any benefit having tank between circulator and boiler isolation valve?

HomerJSmith

10", a force of habit, I guess. Creates a laminar flow into the pump rather than a turbulent flow. Mostly dealing with certain fittings.

The manufacturers diagram is ok as that is probably a high mass, low head boiler. Although, I would prefer the connection at #13 on figure 11.

On figure 12 the dia shows the pump, either, pumping into the boiler or pumping away from the boiler. I would prefer pumping into the boiler with the E-tank where it is depicted.

Boiler manufacturers sent their boiler out with the pump on the input to the boiler. The fixed speed pump was a guess as to the pumping needs of the sys and thousands went out that way. With out some flow control, sonic or not, something was needed to get the flow right.

Remember, flow is the conveyor belt of heat energy transfer.

shredmaster

HomerJSmith said:

10", a force of habit, I guess. Creates a laminar flow into the pump rather than a turbulent flow. Mostly dealing with certain fittings. The manufacturers diagram is ok as that is probably a high mass, low head boiler. Although, I would prefer the connection at #13 on figure 11. On figure 12 the dia shows the pump, either, pumping into the boiler or pumping away from the boiler. I would prefer pumping into the boiler with the E-tank where it is depicted. Boiler manufacturers sent their boiler out with the pump on the input to the boiler. The fixed speed pump was a guess as to the pumping needs of the sys and thousands went out that way. With out some flow control, sonic or not, was needed to get the flow right.

I have figure #12, the only different is that I use webstone isolation flange with a drain. Therefore, expansion tank is above isolation (position A in my drawing) instead of after the boiler isolation. Is there any disadvantage having the expansion tank above the boiler isolation as oppose to the recommendation by the manufacturer?

HomerJSmith

So, the two valves with handles in your drawing are isolation valves and one has a hose bibb attachment? We usually put isolation flanges on pumps so that we can change out the pump without draining down the sys. We would put a fully ported ball valve on one side of the boiler and on the pump side put the Webstone isolation flange. That would allow minimum fluid loss when removing the boiler. I put isolation flanges on both sides of the pump for the same reason.

I would want the E-tank connected on the part of the sys that doesn't get drained. On fig 11, I would want the present tank connection with an isolation ball valve after the E-tank and before the boiler on the main line and isolation valves on the pump. Of course, I would shift the tank to the bottom of 13 ( the air eliminator), but still put the boiler isolation valve in.

On figure 12, I would use isolation valves on the pump, pumping into the boiler with the drain on the valve on the input side of the pump and a isolation ball valve on the supply pipe, exiting the boiler. then. one could flush the sys with street water if need be.

The advantage is that the tank and contents remain part of the sys.