B
Bernie2
Some of the cold screw down stop taps where intended to act like a none return valve by having loose washer jumpers.
The water entered through the seating by pushing the jumper up in the air any backflow is supposed to force it back down onto the seating stopping backflow into the main water.
Many screwed down main water stop cocks still use the same principle today, but they are not classed as none return valves.
Incidentally you can find them on some old bath taps as well. You usually find out when you nearly blow your brains out blowing against a closed valve when your trying to clear air locks, or the hose jumps off when you try to force water down the pipe to clear air locks.
They can also be found on some main storage cisterns preventing you blowing air out of the pipes into the cistern also to clear air locks.
The water entered through the seating by pushing the jumper up in the air any backflow is supposed to force it back down onto the seating stopping backflow into the main water.
Many screwed down main water stop cocks still use the same principle today, but they are not classed as none return valves.
Incidentally you can find them on some old bath taps as well. You usually find out when you nearly blow your brains out blowing against a closed valve when your trying to clear air locks, or the hose jumps off when you try to force water down the pipe to clear air locks.
They can also be found on some main storage cisterns preventing you blowing air out of the pipes into the cistern also to clear air locks.
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