Expansion tank replacement with a what is that?

Bwebb

I need to replace my leaking expansion tank. When I was investigating it I see that there is this brass (assuming) triangle shaped valve? with pipes coming from all sides. What is this? Do I need it?

There is also a ball valve in this bermuda triangle of pipes connected to my expansion tank. I don't see what it can do. It appears to be connected in a loop with itself.

RJ_4

amtrol

The triangle valve is a Amtrol (Fill - trol) valve, it is an auto feed valve with a built in check valve, see Amtrols website to see how it works. Your system was designed using this so leave it in. Changing the tank safely  will most likely require lowering system press.. and water temp. remember if the diaphram in the tank has leaked the tank will be extremely heavy.   Look up past posts on replacing ex-pansion tanks, remember the hardest part of this job may be to getting the air out of the system after the tank has been replaced. This is a job for a pro

Plumdog_2

a heads up....

Indeed, it is a fill valve and pressure reducing valve. The tank will have a straight thread with a shoulder and seal; but a new tank will have 1/2' (tapered) pipe thread, and may not work. They are sold as a unit most of the time. I usually junk it if it doesn't allow flow, and replace it with a fill valve/backflow combination, using valves before and after to allow easier service. Not for DIY unless you study up on it first!