The majority of WCs are fed with their flush water by means of a direct action cistern. The water supplies the system via an inlet valve. The inlet valve is opened and closed by the action of a hollow ball float connected to the end of a rigid arm. As the water starts to rise in the cistern, the float lifts until the other end of the arm shuts off the valve and stops the water feed. To operate the flush a lever is depressed, and this is connected by a wire to a rod attached to a perforated plastic or metal plate at the bottom of an inverted U-bend tube (the siphon). When this plate begins to raise, the perforations become sealed by a fitted flexible plastic diaphragm (flap valve). The plate can now displace a body of water over the U-bend to commence the siphoning process. The diaphragm lifts under the pressure of the water behind it and now the contents of the cistern flow up through the perforations in the plate, over the U-bend and down the flush pipe. As the water level in the cistern falls, so does the ball float, and opens the inlet valve which begins to fill the cistern. A Plumber can fix any cistern issues. There are some issues connected with this type of cistern, but they are easy to resolve. Slow or noisy filling can often be rectified by replacing the ball float inlet valve. If the WC will not flush unless the lever is used constantly, the flap valve usually needs to be replaced. If the flushing lever feels very loose, check that the wire link on the end of the flushing arm is still in one piece. If water is running continuously into the WC pan, check the condition of the washer at the base of the siphon. Plumbers are skilled professionals.

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