Flush valve or cistern? A guide to choosing your flushing system
Compare cisterns and flush valves, understand top-entry and back-entry connections, and choose a flushing arrangement for stainless steel toilets and urinals.
Basterfield EngineeringUpdated
Flush valve or cistern: what is the difference?
Start with the fixture: its flush inlet, drainage outlet and intended installation. Then check the water supply, space, operating control and maintenance access. Use the selected model's specification and drawing to confirm the complete combination.
A conventional gravity cistern stores water before releasing it into the pan, then refills between flushes. A direct flush valve delivers water from the pressurised supply during the flush, without a separate storage cistern. The valve needs sufficient pressure and flow while operating; the cistern needs a suitable filling supply and time to refill.
Here, flush valve means the direct flushing system offered as an alternative to a separate cistern. A cistern also contains an internal flushing mechanism, sometimes called a flush valve. These are different purchasing decisions.
| Selection question | Gravity cistern | Direct flush valve |
|---|---|---|
| Water source during flushing | Water stored in the cistern | The pressurised supply |
| Space to plan |
Top entry and back entry describe the flush inlet
Top entry means flushing water enters through the fixture's top connection. Back entry, also called rear entry, means it enters through a connection at the rear. Match the flushing arrangement to that inlet.
These terms do not describe where fresh water enters a cistern. For example, the B17110(L380-DPB) cistern serves top-entry WC pans but has a side water-supply inlet.
The drainage outlet is another separate choice. Both B17642 pedestal toilet models have back-entry flushing: B17642(P) has a horizontal P-trap waste outlet, while B17642(S) has a vertical S-trap waste outlet. Specify the flush inlet and waste outlet separately.
Exposed or concealed is a separate choice
An exposed installation leaves the valve or cistern on the room side. A concealed arrangement places components behind a wall or within a service space, with an appropriate operating control and maintenance access.
Back entry does not automatically mean concealed. The Walcro 106B is an exposed back-entry valve; the Walcro 103LC is a concealed back-entry valve. Plan how the connections and operating mechanism will be serviced after the wall is finished.
Match the flushing system to your WC pan
The following are catalogue examples. Confirm the exact model, supply requirements and pipe alignment before ordering. Sharing an inlet direction alone does not establish compatibility.
| Selected fixture | Flushing options | Before ordering |
|---|---|---|
| Compatible top-entry pan, such as B17654(PT) | B17110(L380-DPB) cistern or Walcro 106T exposed valve | Select one flushing arrangement; the WC pan is separate. |
| B17642(P) or B17642(S), back entry | B17110(L380-CPB) cistern, Walcro 106B exposed valve or Walcro 103LC concealed valve | Choose for the site layout, available services and maintenance access. |
| High-level cistern installation | B17112 high-level cistern with pull rod operation | Confirm fixture compatibility, mounting height and flush pipe. |
| B17656(CTP) close-coupled suite | Includes a stainless steel cistern and internal flushing mechanism | Check the suite contents before adding accessories. |
Low-level, high-level and close-coupled cisterns
Low-level and high-level describe the cistern's installation position. Close-coupled describes the cistern and pan arranged together as a suite. Read these descriptions alongside the flushing inlet and drainage details.
The B17110(L380-DPB) and B17110(L380-CPB) are 9-litre low-level cisterns for their respective compatible top-entry and back-entry pans. The B17112 high-level cistern uses a pull rod. The B17656(CTP) suite already includes its cistern and internal mechanism.
Cistern capacity is not confirmation of the delivered volume on every flush. Check the specified flushing volume and settings for the complete cistern-and-pan combination.
Check operating pressure and available flow
The manufacturer's Walcro range sheet lists the maintained-pressure ranges below. These are valve-specific figures, not a guarantee that a building supply will flush the selected pan correctly.
Ask the installer to check pressure during operation, available flow and the effect of other fixtures operating at the same time. A static pressure reading alone is insufficient. The nominal inlet size describes a connection; it does not by itself size the building's supply pipework. Match the flushing volume to the fixture's requirements.
| Valve | Nominal supply inlet | Maintained pressure |
|---|---|---|
| 106T, exposed top entry | 25 mm BSP female | 30–600 kPa |
| 106B, exposed back entry | 25 mm BSP female | 30–600 kPa |
| 103LC, concealed | 20 mm BSP female | 100–600 kPa |
Urinals need their own matching controls
WC and urinal flushing systems are separate selections. For the B17744 bowl urinal range, choose accessories for the selected inlet arrangement. The bowl and flushing accessories are separately priced.
- B17744(T), top entry: one Walcro 103LUR exposed urinal valve and one UR15TP 15 mm offset flush pipe per bowl. Include the pipe when selecting this valve arrangement.
- B17744(B), back entry: one B17744(155UW) concealed 15 mm push-button flush system per bowl.
What to confirm before requesting a quotation
Send the selected fixture code and site details so the proposed combination can be checked. Include a drawing or photograph of the connection positions where available.
- Exact fixture model, top-entry or back-entry flush inlet, drainage outlet and mounting arrangement.
- Preferred cistern or direct valve, and exposed or concealed installation.
- Available supply pressure and flow, checked against the selected system.
- Connection positions, wall space, flush-pipe alignment and maintenance access.
- Operating control and position, including handle side and reach requirements for accessible layouts.
- Included and separately specified parts: cistern or valve, flush pipe, bung or adaptor, controls, toilet seat and fittings.
Can I replace a cistern with a flush valve?
Possibly, if the fixture, connections and supply suit the proposed valve. Have the installer assess pressure during operation, flow and pipework before choosing a replacement. Check the complete installation rather than assuming the new valve can use the old cistern's supply connection.
Is a flush valve always more water efficient?
Compare the specified flush volume and performance of complete systems. The system type alone does not establish water consumption. An unsuitable setting can leave the fixture needing another flush; do not infer tested consumption from cistern capacity alone.
Are the flushing system and toilet seat included?
Check the selected product's specification. The separate WC pans illustrated here require the flushing system to be specified; the B17656(CTP) close-coupled suite includes its cistern and internal mechanism. Check seat inclusion separately.
Handle orientation is also model-specific. The B17110(L380-DPB) has a right-hand handle as standard; request a left-hand handle when ordering if required.
Get help matching the fixture and flushing system
Browse the cisterns and flush valves range or request a quotation from the relevant product page. Include the fixture code, preferred arrangement and available supply details. Confirm the final connection and installation requirements before ordering.