sort of..
vac is not like pressure or liquid. If a line is under a vacuum the whole thing, branches, different size lines, chambers, everything is under the same vac. Only time that changes is when there is an increase in pressure from a leak or a servo that may allow air to enter the system. Otherwise, thru the check valve and the entire vac system there will be similar levels of low pressure.
The check valve is'nt complicated. Its just a very lite spring against a plunger/seal that opens as air moves from one side to the other. IF air were to try to move the opposite direct the plunger/spring closes the passage. Normally the valve is closed until vac from the engine pulls against the plunger and opens it. Once the "low pressure" has been generated on the other side of the valve, its everywhere. Diaphrams move, servos move, work takes place. Basically the engine sucks all the air out of those hoses and lines and that is used as a power source to actuate small devices like dash vents or cruise controls. This is exactly the same thing as air brakes on a truck, just the opposite. Vac is a powerful source of power BUT, to utilize it effectively you have to have a large enough diaphram to transition the low pressure to some form of mechanical action. Because HIGH pressure is easier to apply and is almost limitless, you do not see vac used in things that require lots of power because vac does have a LIMIT and its harder to generate and maintain a steady vac...Max is about 29.3 in/hg (IIRC). Thats about as much as can be done easily on earth..
Pressure on the other hand can build until liquids form. So pressure can do more work, as in braking systems. Simple compressor, limitless supply of gases. Pressure is very easy to work with as a power source. Takes too much work to generate a vac unless it happens to be a by-product of some other action thats already present...like a running internal combustion engine.
Back at the ranch...
that check valve has little to do with any thing. Its just there to stabilize the vac so the vent doors don't move everytime the throttle does or engine rpm changes. The vac "ball" or resevoir is there to act as a dampener and absorb some of the pressure spikes to help maintain a steady low pressure in long systems or where long lines exist or larger diaphrams that might have a momentary effect on other things as they move. Its size is no accident. The remainder of the hvac system has a resevoir as well...the tubes and larger hoses that are used in other underhood vac systems store enough "void" to keep the system stable.
Cruise diaphram..It needs a stable vac because its trying to hold a steady speed even though the engine may be trying to react to varying conditions that effect the manifold vaccum level, so the resevoir manages the vac to help the CC stay stable and maintain the set speed. It adjust constantly to the changing conditions. The largest on the car is the brake booster. The brake booster also has a check valve so the power level does not fluxtuate when your foot in on the pedal. Thats also why its so big...so there is plenty to spare. D/C the booster for a day and see just how much work a good diaphram really does...
I've been in the FSM trying to find how or how much vac the actuators hould need and how to test properly. So far, its unclear. There is no set amount of vac that can be applied with an expected result. Assuming that the normal vac range is similar to what manifold vac is on average, that would have to be what the actuators should be working with. As far as how long they should hold vac, thats also not described. In my experience, I have seen systems that would hold the vac for several seconds up to several minutes...even longer after the engine was shut off. Much of that depends on check valves and resevoirs. As stated earlier, whatever vac is present is the same throughout the system.
My question after thinking about this, was:
If vac was applied to an actuator, should that actuator hold that vac and its position for a given period of time? As a test of its power and ability to seal against leaks..?
My conclusion after reading the FSM on this....
I suppose that IF the actuator works and does its job at the normal vac level, and operates as it should, releasing the mechanical device as it should then if it leaks a little, thats ok since vac is always replaced with a running engine. It takes a pretty large diaphram leak to have a negative effect on the engine...like the brake booster for example. I've seen many leaks that changed idle slightly, but higher rpm there was no difference since there is so much air being moved thru the manifold...the leak is insignificant above idle.
Hope this helps...don;t know how it would...but hope it helps with the current question...
which was, what again?:L
