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Originally Posted by signalredcoupe
I agree, but as I stated, the schader valve does have a spring to hold it closed & will overcome the approx. 1/3 to 1/2 lb of force of the ambient atmosphere trying to enter the vacuumed system. Unless of course, the schader valve spring is incredibly weak. Paul.
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& I may be wrong, but the spring only works to seal when the hi pressure comes from inside the system..with 230 psi freon in the system, the spring poppet will be pushed shut from the freon inside and it can't escape.
With vacuum in system, the high pressure is on the other side of the system and the spring can't close because pressure inside the system (-30 psi) due to the vacuum is less than pressure from the atmosphere(14.7 psi). The spring simply cant be forced shut by a vacuum. if anything the vacuum will pull the spring poppet open. Therefore atmosphere goes into the vacuum and the vacuum disappears.
The only way you can beat this is to leave your manifold guage assembly attached after drawing the vacuum and then close the manifold. Directly after disconnecting the vacuum pump from the yellow middle hose, attach the pressurized freon to the yellow hose, open the cans and then open the manifold.Even then u might get 1 psi leakage, but i can live with that....