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Toilet tank parts (C) DanieL FriedmanToilet Flush Mechanisms
How Flush Toilets Work, parts & features

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Toilet cisterns & flush tanks:

This article explains how a flush toilet operates and describes the types, parts, and operation of the toilet cistern or toilet flush tank.

This article series describes the different types and models of toilets: historical or old toilet types, wooden high wall-tank toilets, conventional reservoir tank toilets, low-flush toilets, water saving toilets, back-flush toilets, up-flush toilets, and even chemical toilets. Here we explain how to diagnose and repair problems with toilets, leaks, flushes, odors, noises, running and wasted water.



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Toilet Tank-Reservoir (Cistern) Flush Toilets & How They Work

Side valve flush lever toilet (C) D Friedman

Tank reservoir toilets have been in wide use since the 1940's and some tank reservoir or cistern flushed toilets have been in use for more than 100 years. At left we see the flush handle on a modern tank or cistern operated gravity flush toilet.

[Click to enlarge any image]

While there have been improvements in toilet tank fill valves, flush valves, floats, and water savings, the design has remained about the same.

Here we describe the basic sequence of operation when a toilet is flushed and we explain the function of the key toilet flush and fill valves and diverter / overflow tubes.

Article Contents

What Happens when a Toilet is Flushed: 3 Basic Operations

  1. Flushing the toilet opens the flush valve: A flush lever moves an arm to lift a flapper valve or tank ball to permit water to rush into the toilet bowl below, washing away waste into the sewer pipe. [Other toilets may use a siphon-flush valve to activate the flush cycle.]

    Details are at TOILET FLUSH VALVE

    At the end of the flush cycle, a float arm, or a float moving on a vertical stalk (newer valves) drops to open a valve permitting the toilet tank to refill with water.
  2. Re-Filling the Toilet Cistern or Tank: When the toilet tank water level reaches the proper level, the float closes the toilet tank fill valve.

    Details are at TOILET FILL VALVE
  3. Additional Water Enters the Toilet Bowl: during the re-filling of the cistern or toilet tank, as long as the toilet fill valve is open to allow water to enter the toilet, most designs use a small diameter tube to direct a portion of the incoming water down the cistern tank overflow tube (see sketch above) and into the toilet bowl. This extra water helps assure a proper level of water in the toilet bowl to prepare it for its next use.

    Details are at TOILET DIVERTER & OVERFLOW TUBE

Following our description (below) of how the flush valve works and how the fill-valve re-fills the toilet tank or cistern we describe the operation of a variety of other toilet types including:

Toilet Flush Valves

Flapper valve controls toilet flush (C) Daniel FriedmanWhat happens inside the toilet cistern / tank when the toilet is flushed?

When a gravity type toilet is flushed, the toilet flush valve sends water out of the toilet tank or cistern (conventional flush valves) or directly from the building water supply without a toilet tank or cistern (flushometer valves) into the toilet bowl below to flush waste into the building drain system.

The two most common toilet flush valves used on toilets that make use of a tank or cistern are the flapper type toilet flush valve (illustrated just below) and the tank ball type toilet flush valve (illustrated further below).

Flapper type toilet flush valve: (photo at left) (see below) is a toilet flush valve that closes the opening at the bottom of the toilet tank using a semi-round flapper (usually rubber) rather than the rounded tank ball shown in the sketch.

Like the toilet tank ball type flush valve (illustrated in the sketch below), the flapper valve is pulled up to open the toilet reservoir tank drain opening to send flush water down into the toilet.

The shape and position of the flapper cause it to remain in the open position until the water level in the toilet tank drops to nearly empty, then the flapper "flaps" down over the drain opening to stop the toilet flush cycle and to permit the toilet fill cycle to begin anew.

Toilet tank parts (C) DanieL FriedmanOn modern tank type toilets we see mostly flapper valves; tank ball flush valves (below) are still found on older equipment however.

Once the flapper valve is closed, water pressure from the filling toilet tank or cistern presses the valve face against the valve seat, holding it shut against leakage.

Toilet flush valve repair: If your toilet is "running" and has a flapper valve, often the leak between cistern and bowl is at this valve. Try cleaning the valve seat. If that doesn't work, a new flapper valve may cure the leak.

Other repairs include an epoxy add-on new flush valve seat that glues atop the existing one, or else disassembly of the toilet tank to replace the entire assembly.

If your toilet uses a tank ball flush valve, be sure that the lift rods move freely and are not bent or binding. The opening in the rod guide (see sketch at left) that guides the lift rod should be centered over the center of the tank ball.

Tank ball type flush valve: the control that sends water from the toilet tank (or building water supply) into the toilet bowl to flush away waste. There are many models of flush valves, using varying designs. A tank ball flush valve assembly is shown in the sketch at above left.

In a traditional side float flush valve assembly (sketch at left) the toilet is flushed by pressing on a handle outside the toilet tank that lifts a trip lever that pulls a chain or rod that lifts a tank ball or a tank flapper that otherwise seals the bottom of the toilet tank.

For modern toilets important are designs that conserve water either through the valve design itself (see Top Flush Control Toilets) or by means of a plastic "dam" around the valve assembly.

Toilet Flush Valve or Flush Control Operating Details

Flapper valve controls toilet flush (C) Daniel FriedmanThe toilet flush valve sends water out of the toilet tank or cistern (conventional flush valves) or directly from the building water supply without a toilet tank or cistern (flushometer valves) into the toilet bowl below to flush waste into the building drain system.

The two most common toilet flush valves used on toilets that make use of a tank or cistern are the flapper type toilet flush valve (illustrated just below) and the tank ball type toilet flush valve (illustrated further below).

Flapper type toilet flush valve: (photo at left) (see below) is a toilet flush valve that closes the opening at the bottom of the toilet tank using a semi-round flapper (usually rubber) rather than the rounded tank ball shown in the sketch.

Like the toilet tank ball type flush valve (illustrated in the sketch below), the flapper valve is pulled up to open the toilet reservoir tank drain opening to send flush water down into the toilet.

The shape and position of the flapper cause it to remain in the open position until the water level in the toilet tank drops to nearly empty, then the flapper "flaps" down over the drain opening to stop the toilet flush cycle and to permit the toilet fill cycle to begin anew.

On modern tank type toilets we see mostly flapper valves; tank ball flush valves (below) are still found on older equipment however.

Toilet tank parts (C) DanieL FriedmanOnce the flapper valve is closed, water pressure from the filling toilet tank or cistern presses the valve face against the valve seat, holding it shut against leakage.

Toilet flush valve repair: If your toilet is "running" and has a flapper valve, often the leak between cistern and bowl is at this valve. Try cleaning the valve seat. If that doesn't work, a new flapper valve may cure the leak.

Other repairs include an epoxy add-on new flush valve seat that glues atop the existing one, or else disassembly of the toilet tank to replace the entire assembly.

If your toilet uses a tank ball flush valve, be sure that the lift rods move freely and are not bent or binding. The opening in the rod guide (see sketch at left) that guides the lift rod should be centered over the center of the tank ball.

Tank ball type flush valve: the control that sends water from the toilet tank (or building water supply) into the toilet bowl to flush away waste. There are many models of flush valves, using varying designs. A tank ball flush valve assembly is shown in the sketch at above left.

In a traditional side float flush valve assembly (sketch at left) the toilet is flushed by pressing on a handle outside the toilet tank that lifts a trip lever that pulls a chain or rod that lifts a tank ball or a tank flapper that otherwise seals the bottom of the toilet tank.

For modern toilets important are designs that conserve water either through the valve design itself (see Top Flush Control Toilets) or by means of a plastic "dam" around the valve assembly.

Flushometer or flush-o-meter toilet valves & toilets: these tankless toilets are flushed using building water pressure and a vacuum-breaker valve control.

See FLUSHOMETER VALVES for TOILETS URINALS for details about these valves and how they are adjusted or repaired.

Also see Toilet Types, Flush Methods for a discussion of variations in toilet flush mechanisms & methods.

Toilet fill valve and flush valve details (C) D Friedman  & Urrea Fluye, MexicoGravity flush toilet: (sketch at left) the conventional and most common water-operated toilet world-wide is flushed by water that flows (from a reservoir tank) into the toilet bowl by gravity; the reservoir tank must be above and is typically attached to or part of the toilet assembly, though early flush toilets (illustrated below) placed the flush tank much higher on the wall in an effort to obtain a more cleansing flush for early bowl designs.

When the toilet is "flushed" using its handle, a flush control valve (see "tank ball in our sketch above) opens to send water from the reservoir into the toilet bowl to flush it clean.

At the end of the toilet flush, a ball cock valve or equivalent (#1 & assembly "C" in our sketch at above-left) refills the toilet tank from the building cold water supply (the fat blue arrow in our sketch).

Hatbox toilet: a tankless toilet design by Kohler (illustrated below) that uses an electric pump to deliver flush water and adequate water velocity

Overflow tube, toilet: the overflow tube (item #8 in our sketch at left), is found on virtually all modern toilet flush control valve assemblies. This tube prevents a malfunctioning toilet tank refill assembly from flooding the building. (Unfortunately if the toilet drain is clogged and the toilet overflows you'll have a different sort of flood
See TOILET OVERFLOW EMERGENCY.)

During toilet tank re-fill, if the tank over-fills, the overflow tube (blue #7 in sketch at left) will excess water from the toilet reservoir tank down the overflow tube (#8) into the toilet bowl. This is a critical function since otherwise if the toilet fill-valve malfunctions water entering the toilet tank will fill the tank to overflowing and leak into the building. But if your toilet is "running" the problem may be just that - the fill valve is sending water continuously into the tank where it enters the overflow tube.

A second feature of most toilet fill valve assemblies and overflow tubes is that some water will be diverted from the fill valve into the overflow tube during the toilet tank fill-cycle - see the small curved blue tube marked #7 in our sketch above). This makes sure there is enough water in the toilet bowl before its next use.

Pressure-assist flush toilet: the toilet is flushed by water that is given a velocity boost by a pressure system using a pump,compressed, air, or other means. Typically pressure-assist toilet designs are found on water-saving low-flush-volume toilets.

Flushometer or flush-o-meter toilet valves & toilets: these tankless toilets are flushed using building water pressure and a vacuum-breaker valve control.

See FLUSHOMETER VALVES for TOILETS URINALS for details about these valves and how they are adjusted or repaired.

Also see Toilet Types, Flush Methods for a discussion of variations in toilet flush mechanisms & methods.

Toilet Fill Valves

Ball cock valve / Concentric Float Valve

Toilet ball cock valve assembly photo (C) D Friedman Concentric float toilet fill valve (C) Daniel Friedman

The toilet ball cock fill valve shown in our photo at above left is a traditional side-float brass ball cock valve by Urrer is the control that refills the toilet tank after a flush. the rod that carries the float, the float itself and other toilet parts are not shown in this illustration.

Concentric float toilet fill valves (photo at above right) omit the rod, side-arm, and float ball. Instead a float rises on a vertical shaft that also supports the fill control valve.

In our photo my finger is pressing up on the lever that stops the flow of water into the toilet tank. You can see that an adjustable rod on the float (below the valve) will push up this stop lever on its own as the water level in the tank rises.

In some small-tank toilets we found that installing a concentric float toilet fill valve solved a problem of frequent jamming of the older side-float valve assembly whose float or rod would rub against the overflow tube or the toilet tank sides, jamming and giving recurrent "running toilet" problems.

Toilet Fill Valve Operation

The toilet fill valve admits water into the toilet reservoir tank or cistern to refill the cistern following a toilet flush. Most fill valve designs also send some water through the overflow tube and into the toilet bowl during cistern re-fill.

Two common fill valve designs in current use are the ball-cock toilet fill valve and the concentric float toilet fill valve. Both of those designs are illustrated above. Synonyms for toilet fill valves include: ball cock valve, concentric float valve, toilet water supply valve, toilet tank fill valve.

Toilet tank float arm and float ball (C) Daniel Friedman

Toilet Cistern / Tank Float-Controlled Fill Valve

The toilet tank float assembly activates the toilet fill valve as water level in the toilet tank or cistern drops during and at the end of a toilet flush.

Illustrated above at concentric float toilet fill valves, the float for that device is a cylinder that moves down or up on a vertical shaft as tank (cistern) water level in the cistern falls or rises, to open or close the fill valve itself.

A ball cock toilet fill valve is opened by movement of a float arm rod attached to a round float ball (illustrated at left) that drops as water level in the cistern falls during a flush, and the ball cock valve is closed as the float rises, lifting the rod to which it is attached as the water level in the toilet tank rises to the fill line.

In our photo (above left) a white plastic ball cock fill valve is shown in lieu of the older traditional brass and bronze ball cock valve illustrated earlier on this page.

Toilet tank float adjustment procedure

Adjust the float lever angle so that combined with the ball cock shutoff adjustment the assembly stops water flow into the water tank when water reaches the fill line marked on the tank.

If you do not see a fill line marked in the toilet cistern, set the fill level at least 1/4" below the top of the overflow tube. Also be sure that the float ball moves freely in the toilet tank. If the float ball rubs on the tank sides or end it is likely to jam and the toilet may not fill properly, or the toilet may run continuously.

Toilet Overflow Tube & Diverter Tube

Toilet Diverter Tube & Overflow Tube Bowl-Fill Operation

Toilet tank float arm and float ball (C) Daniel Friedman Toilet Overflow Tube, Brew Moon, New Zealand (C) Daniel Friedman

[Click to enlarge any image]

Overflow tube, toilet: the overflow tube (photo above left), is found on virtually all modern toilet flush control valve assemblies. This tube prevents a malfunctioning toilet tank refill assembly from flooding the building. (Unfortunately if the toilet drain is clogged and the toilet overflows you'll have a different sort of flood
See TOILET OVERFLOW EMERGENCY.)

External toilet overflow tubes: On some toilets such as the toilet found in the Brew Moon restaurant in New Zealand, a separate overflow drain is provided and is connected to a waste line (blue arrows in our photo at above right). This toilet cistern overflow drain has the sole function of preventing the toilet cistern from over-filling and spilling into the building.

During toilet tank re-fill, if the tank over-fills, the overflow tube (blue #7 in sketch at left) will excess water from the toilet reservoir tank down the overflow tube (#8) into the toilet bowl. This is a critical function since otherwise if the toilet fill-valve malfunctions water entering the toilet tank will fill the tank to overflowing and leak into the building. But if your toilet is "running" the problem may be just that - the fill valve is sending water continuously into the tank where it enters the overflow tube.

Diverter tube empties into Overflow Tube: A second feature of most toilet fill valve assemblies and overflow tubes is that some water will be diverted from the fill valve into the overflow tube during the toilet tank fill-cycle (Thin blue arrow in the photo at above left). This makes sure there is enough water in the toilet bowl before its next use.

Other Toilet Flush Methods & Types

Here are descriptions of additional toilet designs that use different flush methods from those described above.

Back Flush or Rear Flush Toilets Using a Reservoir Tank

A back-flush toilet that does use a reservoir tank is also produced for special situations such as a location that prohibits installing a drain line in the floor below the toilet. At below left we illustrate a back-flush toilet installed in a Two Harbors Minnesota home built in the 1960's.

Our second back-flush toilet photo (below right) shows a reservoir-tank back-flush toilet located in a basement in the Hudson Valley of New York. In this basement the sewer line ran just a few inches above the basement floor. The plumber mounted a back-flush toilet on a short concrete pedestal, raising it just enough to flush into the nearby sewer line found in the wall behind the toilet.

Back Flush Toilet with reservoir (C) Daniel Friedman Back flush flush valve toilet in Norway (C) Daniel Friedman

At above left is a photo of a modern tankless, back-flush, flush valve operated toilet installed in Molde, Norway. This toilet is also a back-flush model, sending waste out of the bowl towards the rear of the toilet and into a waste line in the building wall rather than in the floor.

The flush control for this tankless (cisternless) back-flush toilet is that round button just above the toilet tissue holder. Other water operated tankless toilets that are not back-flush models are discussed at Flushometer Toilets & Urinals.

At above right is a rear-flush toilet manufactured by Crane and installed in the Mansfield Hotel in New York City. Other modern brands of rear-flush toilets include American Standard, Burdett, Crane, Gerber, Kohler, Sani-Flow, Toto.

Up-Flush Toilets Located Below the Sewer Piping, No Toilet Tank

Up Flush Toilet (C) Daniel FriedmanA variation on the flush valve toilet is the up-flush toilet used in bathrooms whose toilet was located below the building's sewer line exit to the sewer or septic system.

An up-flush toilet relies on building water pressure to force the waste from the toilet up to a higher sewer line.

Because an up-flush toilet that relies on building water pressure to work forms a cross connection, these toilets are not permitted by plumbing codes in most jurisdictions.

In our photo of an up-flush toilet you can see the flush control lever mounted on the wall at the upper right.

Like the modern flush-valve toilet shown above, the up-flush toilet is also a back flush or rear-flush model. But don't confuse the two.

The flush valve toilet shown above does not form a cross-connection, drains into a gravity-sewer line rather than an elevated sewer line, and it is permitted by current plumbing codes.

 

Top Flush Dual-Flush Control Toilets

Details about water conserving or water saving toilets begin at TOP FLUSH TOILETS and at DUAL FLUSH TOILETS.

Separately at LOW WATER USAGE TOILETS we discuss toilet that use a reduced water quantity, and at FLUSHMATE TOILETS we discuss power-assisted flush toilets that also conserve water. Excerpts are just below.

Water saving models (typically a pair of buttons giving different flush volumes) illustrated below. Dual-flush water saving toilets typically deliver 1.1 gallons to flush liquid waste or 1.6 gallons to flush solids.

Top flush flush valve toilet Glacie Bay (C) Daniel Friedman Top flush flush valve toilet Glacie Bay (C) Daniel Friedman

Low Water Consumption Toilets - Water Saving Toilets

Water saving toilet using internal reservoir (C) Daniel Friedman

Details are at
LOW WATER USAGE TOILETS where we discuss toilet that use a reduced water quantity, and at

FLUSHMATE TOILETS we discuss power-assisted flush toilets that also conserve water. Excerpts are just below.

Also see water conserving or water saving toilets that use different flush volumes for urine than for solid waste, now discussed at
TOP FLUSH TOILETS and at

DUAL FLUSH TOILETS.

Water saving toilets use several strategies to reduce the volume of water used in flushing away waste: varying flush volume, pressure or power assisted flush using a small flush water volume, and reduced flush water volume using a reservoir barrier in th cistern or toilet tank.

At LOW WATER USAGE TOILETS we give the various water volumes used by each toilet type and design.

Air & Water Powered Flush Toilets (Pressure Assist): the Sloan Flushmate

Sloan Flushmate power flush toilet tank & controls (C) Daniel FriedmanDetails for power assist or power flush toilets like Sloan's Flushmate are found\ at FLUSHMATE TOILETS

Power flush toilet model shown in our photo below: Sloan Flushmate® Model M-101526-F3 using a 1.6 gpf or 6LPF toilet flush volume. Other Flushmate® toilet models (Flushmate IV) use less than 1 gallon per flush.

The FLUSHMATE® system traps air and as it fills with water, it uses the water supply line pressure to compress the trapped air inside. The compressed air is what forces the water into the bowl, so instead of the “pulling” or siphon action of a gravity unit, the pressure-assist unit “pushes” waste out. This vigorous flushing action cleans the bowl better than gravity units. - quoted from www.flushmate.com, retrieved 2/2/2014

 

Electric Flush Toilets & Pressure Assisted-Flush Toilets

Our toilet photographs below illustrate a tankless, electric-flush toilet produced by Kohler. As you can see (below-left) the toilet may be a little unfamiliar to new visitors at the New Hampshire inn where this unit was installed.

Pressure-assisted flush toilets may use water pressure from the water mains to improve the flush cleansing of the bowl, or they may use a pump or an air bladder system that is in turn operated by water pressure. By providing a more aggressive and higher velocity flush than a gravity flush toilet a pressure-assist system generally uses less water, ranging from 1.1 to 1.4 gallons.

Kohler Purist Hatbox Toilets

Electric flush Kohler toilet (C) Daniel Friedman Electric flush Kohler toilet (C) Daniel Friedman

For a newcomer, flushing this Kohler hatbox toilet could be a bit of a mystery. Searching for a flush lever or button finally leads to a round silver button located on the right side (if the user is seated) of the unit (photo, below right).

Pushing the flush button on the older unit that we tested produced an aggressive and roaring "flush" along with a bit of pump noise. Other literature describes these toilets as "quiet". Our photo at below left gives a clue about how this toilet was powered.

Electric flush Kohler toilet (C) Daniel Friedman Electric flush Kohler toilet (C) Daniel Friedman

Newer versions of the electric flush toilet made by Kohler include a reservoir tank and an electric pump that moves water from the reservoir through the bowl and toilet trap. This design offers a toilet that provides a low profile but nonetheless a very powerful flush in a compact design.

The Kohler hatbox toilet installation we examined had been in place for some time; this product is still available at a typical retail price of $2,725.

Flushometer Toilets & Urinals

Flushometer toilet or urinal valve (C) Daniel FriedmanTankless flush-o-meter valve toilets, in widespread use in North America since the 1920's, and unlike tank reservoir toilets, do not include a reservoir tank of water.

The flushometer valve is particularly suitable to public restrooms since there is no delay between toilet uses waiting for a reservoir tank to refill. Typical flush volume is 1.6 gallons.

Details are at FLUSHOMETER TOILETS & URINALS

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Continue reading at TOILET FLUSH VOLUME or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see TOILETS, INSPECT, INSTALL, REPAIR. This toilet buy, install or repair guide article series discusses the cause, diagnosis, and repair of toilet problems (water closet problems) such as a toilet that does not flush well, clogged toilets, slow-filling toilets, running toilets, loose wobbly toilets, and odors at leaky toilets.

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TOILET FLUSH OPERATION at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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