As far as opening and closing nothing, just make sure your hose is filled with water it is eaiser to begin vacuuming, normally we attach the hose to the vacuum that goes in the pool then attach the hose to the skimmer then begin vacuuming if we do not loose our prime, if the pressure gauge on the filter is reading low you can probaly can start vacuuming if it is reading mid to high pressure it sometimes is best to backwash before vacuuming.
The vacuum on a pool connects into the vacuum plate that fits over the skimmer basket on the side of the pool. My vaccum attaches in the bottom of the skimmer UNDER the basket. Different types of skimmers.
Sounds like you have too much suction in the skimmer. If you have 2 skimmers and have plugged one to vacuum, try taking it out. If you do not have 2 skimmers and have a main drain, try diverting some more of the suction to the main drain. I am not sure why you would be getting wrinkles unless your liner is loose or you have water behind the liner causing this. Hope this helps
You can find the boiling point of mercury in a vacuum using a closed system.
If you have a dedicated suction for the vacuum hose (illegal in Australia) then you close the skimmer to increase suction.
The vents are opened and closed by vacuum. There should be a vacuum line running from the engine to the inside of the Trailblazer. That line is broken somewhere and it is not sending vacuum to the switch. That will cause it to blow to the top of the dash (defroster) and to the bottom (floor.) Find that line trace it back and splice a new line in where it is broken. That should fix the problem.
Old/worn intake manifold gasket and/or damaged/broken/mis-routed hoses attaching to intake manifold.
The brakes on a 97 S-10 are bled by attaching a vacuum pump to the bleeder valves and loosening the valve. The vacuum is then used to draw out air until only fluid is present.
Basically, the amount of vacuum in the intake manifold varies with how much the butterfly valves(either in the carby, or in the throttle body on a fuel injected engine)is opened. If you take your foot off the accelerater, the engine is trying to suck air past the partly closed butterfly, thus creating vacuum. If you are under acceleration and the butterfly is open, the engine is drawing air freely, so manifold vacuum is low. Turbocharged engines have lower vacuum because the air is force-fed, so an electric vacuum pump is sometimes used to run the brake booster.
Engine vacuum will be affected by valve adjustment due to vacuum leakage when valves are not closed at the proper time, when the piston is on a downward stroke. The vacuum would be less that it should be.