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Question about a mixing circuit with fixed premixing

Question about a mixing circuit with fixed premixing

(OP)
Hi everyone,

First of all, sorry for any mistake, I am not a native English speaker.
I am starting an internship and I have been said that I would work on the following cooling circuit:



I've never really worked on hydraulics circuit, so I tried to find some information.
I would like to have a confirmation that what I found is right, and I also still have some questions.

1) First, I found that it's a "mixing circuit with fixed premixing", is it correct? I understand that the fluid flows through A-B-C-D-E-F, that a part of the flow goes trough G, and that a part of the flow also goes through the line under G. In C, there is a mix of the cold water from the bottom and of the warmer water from the right. The fact that some warmer water comes from G also permits to increase the temperature of the very cold water from the bottom. Thanks to that, we can control the valve C from "totally closed" to "totally open", even though the water from bottom is very cold. It facilitates the control : if we just regulated the heat transfer at the top with a throttle, we would have to control very small flows. Is it correct?

2) I wonder why there is a kind of rectangle divided in two on each side of each valve : are they all flanged valve (I saw that the symbol of a flanged valve normally has two lines on each side; here it's two rectangles, but it's maybe just because of the software that was used to make the drawing) ? Beside, what's a flanged valve ? I found many product descriptions, but no clear definition

3) What's the empty circle in the middle of the valves A and H ? Is it a ball valve ? If yes, if you can also help me to understand what's a ball valve..

4) What's the valve B ?

5) Valves F and G : I found that they are called Y pattern valves. Apparently they are interesting because they result in a lower pressure drop. Could you help me to understand that a bit more?

6) What are the "+" signs on F and G ?

7) Here is how I see the role of the different valves:
A is like a resistance to avoid that all the cold water from the chiller comes in this subcircuit. It's apparently cold "balancing".
B : no idea of its function
C is a three-way valve : the output flow is constant (as it's a mixing circuit), and we can control if the water comes 100% from the bottom, or 70% from the bottom and 30% from the right, etc...
G permits to control how much warmer water comes from the right. Is it a one-way valve ?
H is like a resistance to force the water to stay in the circuit and flow through G for example. Without it, the water would just go where there is no resistance, like electricity, and get back to the main circuit.
F : no idea of its function

Thanks very much for your help!

RE: Question about a mixing circuit with fixed premixing

(OP)
The circuit is enclosed in the last message, to directly see it:

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