Mostly suction apparatus with dual head motor, consist a non-return valve, what is its function to have it on the apparatus and not to have it?
It depends on the size and pressure rating as to the material used. Small lower pressure valves can be brass or bronze while larger high press valves will be made from cast steel. Brass can be used for some internals because it is corrosion resistant. It is also softer which makes is good for seating material.
Non return helps to prevent flow back of the material needed for trasportation,also helps to prevent material to be lost when the motor is turned off,ensures maximam flow. Not to have reason all liquid intedend for transportation will flow back when motor is turned off,difficult to ressit materiall in vertical direction.
A non-return valve ensures when you stop the motor that what ever material you have sucked does not return back to it's original location. Take the example of a vacuum cleaner and a bowling ball... If you were to pick up the bowling ball with a vacuum cleaner and then turn the vacuum cleaner off, the ball would fall. However, if you had a non-return valve along the piping of your vacuum cleaner, when you turned the vacuum cleaner off the bowling ball (assuming there is a perfect seal between bowling ball and vacuum cleaner's attachment and the piping of the vacuum cleaner did not leak!) would stay attached to the vacuum cleaner and not fall! Non-return valves in the case of suction apparatus, usually act as a safety device to ensure if the power is lost to the motor, that any vacuum that has been produced is not lost.
