question on NCARB sample #13

[aiwan]

can anyone kindly explain why it's a gate valve rather than a globe valve? thanks!

13.JPG

[Sparky83]

https://www.quora.com/What-is-the-diffe ... lobe-valve

[aiwan]

Thanks Sparky83.
I had originally thought it'd be the gate valve for position 1 (by the service) - was trying to understand why it needs to be an all on/off to the pump? Would all positions (1-4) req a gate valve?

[jaginomoto]

Thanks Sparky83.
I had originally thought it'd be the gate valve for position 1 (by the service) - was trying to understand why it needs to be an all on/off to the pump? Would all positions (1-4) req a gate valve?

It needs to be an all off type of valve at the pump as that is the hot water return to the boiler. You don't need to control (regulate the flow) of the water coming back to the tank when you are servicing the unit. You just want the water to turn off.
At the cold water service line (bubble #1), you may want to install a globe valve there so you can control the amount of water flow into the boiler unit, although as a shut off (on or off valve) over time these tend to fail and water sometimes passes through (leaks).
Typically you would install one prior to the tank (bubble#1) and if like the diagrams shows if the cold water supply line continues onto the other areas (kitchen, Utility, Bath) you would install one after the tee to the tank. This helps in replacing the tank in the future and prevents back flow when servicing.

An angle valve would throttle the flow, as well, as it is pictured it is a globe valve that is just not "in line".
There are angle valves, which use balls, that are turned to shut off the flow, the one shown is not one of them.
There are also pressure release valves, which use springs, none of them are shown.
The question is asking for an in line valve, leaving you with one option.
Hope that makes sense.