Let's Talk about Check Valves....
 

So, as you know I am going twin turbo. I plan to run a vacuum hose from the brake booster port on the intake to a vacuum block, then run all of the vacuum lines from there - including the brake booster. I hear some say yes you need check valves, and some say you don't.

Do I actually need check valves? If so, where?

The brake boost on my car, which was turbo from the factory, has a check valve on it. It is essentially a PCV valve.

The fitting that goes on the end of the hose and presses into the brake booster IS a check valve.

yep- the fitting in the diaphragm is a check.

I do run a check instead of a PCV though.

since I am having a single vacuum hose going to the vacuum block (then everything vacuum related going from there) should I place a check valve between the intake and the vacuum block?

No because then your waste gate would never see positive pressure

My booster did not come with one. I ran a check valve inline to the booster only.

the blend doors on my HVAC are vacuum operated. would all that positive pressure screw them up or should I put a check valve on just that?

I run a ck valve, and oil sep, but only go from intake to PCV valve

I'd consider splitting the vacuum system up. The HVAC needs a check valve, unless you like it switching to the defroster ducts every time you get under a load. There is a GM model (I want to say S10 or maybe Trailblazer, help me here guys) with a check valve on the brake booster that has a port for the HVAC. If you have cruise control, you also will want to check valve that. The others could be run off a good vacuum tree.

not worried about cruise control, I am DBW. I was also told today that my HVAC already has a check valve in it so it looks like I won't need to add any.