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Modifying flush tank system for Cleaner Toilets

[box type=”shadow” ]Maintaining hygiene condition and elimination of the foul smell of the toilets or water closets in washrooms has become a severe problem. Having restrooms with or without toilet alone does not ensure hygienic standards unless the toilets are always kept clean and odour free, says Bangalore-based SK Bhat, retd. engineer and technology educator.


There are three styles of toilets;

• The Wash- down style
• The Wash-out style and
• The Reverse Bowl or Shelf Style

One side of the U conduit has a hollow siphon tube longer than the water in the bowl. The siphon tube connects to the drain. The stagnant water in the bowl acts as a barrier to sewer gas coming out of the sewer through the drain, and also as a barrier for the reflux of waste matter and the entry of rats. Sewer gas is vented through a separate vent pipe attached to the sewer line.

When a user flushes a toilet, the inlet of the syphon (in the old mechanism -flapper valve opens) in the flush tank gets opened and siphons the water from the flush tank quickly to the bowl of the future.

This rapid influx from the tank results in the swirling of the water within the bowl and fills the U-shaped inverted siphon tube mounted in the back of WT and
facilitates the required siphon action. The siphon action quickly siphons all the waste and water from the bowl down the drain. After flushing, the siphoning action stalls and the flush tank is refilled facilitating reuse of the apparatus.

The ballcock or float valve is often used to regulate the filling of the flush tank or cistern. When the fluid level drops, the float descends, levering the valve opening and allowing more fluid to enter. Once the float reached the ‘full’ position, the arm presses the valve shut again. These types of valves are found in almost all types of toilets. The valves are of two main designs, the side-float design and the concentric-float design. The side-float design has been used since over a hundred years. The concentric design that has been recently developed valve is gradually becoming more popular than the side-float design. The sidefloat design uses a float on the end of a lever to control the fill valve. The float is usually shaped like a ball, so the mechanism is called a ball-valve or a ballcock. The float was originally made from copper sheet, but it is now manufactured using plastic. The float is located to one side of the main valve tower at the end of a rod or arm. As the side-float rises, so does the side-float-arm. The arm connects to the valve that blocks the water flow into the flush tank, and thus maintains a constant level in the tank.

The siphon flush system (SFS) invented by Albert Giblin, uses a flush / storage tank. SFS is sometimes referred to as a valve less system, since no flapper type of valve is required. In SFS, the user presses a knob or valve opening mechanism, forcing the water up into the tank siphon passageway which then empties the water in the tank into the bowl. The advantage of a siphon over the flapper valve is that it has no sealing washers that can wear out and cause leaks, so it is favoured in places where there is a need to conserve water. The use of the siphon flush system has the advantage of preventing the wastage of water by millions of litres as compared to the toilets with flapper valves. However, SFS are sometimes more difficult to operate than a flapper valve system because the SFS lever requires more torque than a flapper valve system.

Earlier systems, known as high suite combinations, used a high-water head level tank and were operated by pulling a suspended chain hanging down from a lever attached to the tank. Modern close coupled water tank and bowl combinations were first referred to as low suite combinations. New versions have a stylish low-level tank with a lever that the user can reach directly, or a close-coupled tank that is even lower down and is integrated with the bowl itself. Consistent adaption has improved design and with a focus on water conservation, a flush toilet has been designed recently. This either flushes comparatively less water or a large amount of water. The waste matter from the bowl is washed out to the sewage conduit by flushing water.

Fluid power includes fluid mechanics, fluid kinematics and fluid dynamics. In fluid mechanics, the characteristics of stagnant fluid a fluid at rest is the most important part. Fluid may liquid / in compressible fluid or may be gaseous / compressible fluid in this case water is used. One of the characteristics of water at rest (stagnant water) is that the pressure intensity varies in the vertical direction / plane. The pressure intensity increases with the depth. However, along the horizontal direction / horizontal plane, the pressure intensity will always be constant and its value will be same in all directions.


Let there be an ordinary rectangular cross section big tank with no opening and a small rectangular cross section tank with a small opening beneath. The big tank water be filled with water up to a level of three metres, measured w.r.t. to the bottom of the tank. As a result, the pressure head on the bottom surface will be three metres of water. In the similar way, if the small tank is filled with water up to one and a half metres, the pressure head at its bottom surface will be one and a half metres of water. It is observed that no water flows out from the opening of the small water tank when the small water tank with a small opening at its bottom surface is kept in the big water tank at a depth of one and a half metres from the bottom of the big water tank.

This is due to the high-pressure head in the big tank acting at that water level. This fundamental fact is used to modify the flushing system of WT and to achieve automatic cleaning.

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