RBSE Sec Voc Plumbing key terms

Exactly vertical, checked with a spirit level or plumb bob. Pipes and risers must be plumb so joints align and fixtures hang straight; a plumb wall also keeps stacks centred over their supports.

Exactly horizontal, checked with a spirit level. Drain runs are levelled then tilted to a set fall, so level is the reference from which gradient is measured.

The downward slope of a drain pipe expressed as a ratio such as 1:60, or as mm fall per metre. Correct fall keeps solids moving and prevents blockage; too steep a fall leaves solids behind.

The height of the lowest inside surface of a pipe or drain at a given point, measured from a datum. Comparing invert levels shows whether a drain can flow by gravity to its connection.

A fixed reference mark of known height from which all levels on a job are measured. Setting a stable datum lets walls, drains and fixtures be positioned consistently across the whole site.

A check that a pipe system holds water or air at a specified pressure without loss. It proves joints and fittings are sound before the system is covered, tiled or put into service.

The normal operating pressure a system carries in service, usually in bar or kPa. Pipe, fittings and valves must be rated above this value, with a margin for surges.

A valve that lowers incoming mains pressure to a safe, steady outlet pressure. It protects fixtures and appliances from excess force and reduces noise and water hammer in high-rise supply.

A banging noise and pressure surge caused when flowing water is stopped suddenly by a fast-closing tap or valve. It stresses joints; fitting an arrestor or cushioning valve travel reduces it.

A trapped pocket of air in a pipe that blocks or slows water flow, often after a drain-down or on a badly vented system. Bleeding the high point or correcting the layout clears it.

A tank that stores cold water at atmospheric pressure for supply or flushing. It needs a float valve for refilling, an overflow, a lid and correct air gap to prevent backflow.

A valve opened and closed by a floating ball or a lever arm, used to keep a cistern or tank at a set level. Worn washers cause constant trickling and overflow.

A pipe that discharges excess water to a visible external point when a cistern overfills. Seeing water run from it warns of a faulty float valve before damage occurs.

A physical clear space between the lowest outlet of a tap or supply pipe and the flood level of the receiving vessel. It is the most reliable form of backflow prevention.

Reverse flow of contaminated water into the clean supply, caused by back-siphonage or back-pressure. Prevention uses air gaps, check valves and correctly rated backflow devices.

A valve that allows flow in one direction only, closing automatically when flow reverses. Used on pumps, supply lines and heating circuits to stop backflow and unwanted circulation.

A fitting with two spring-loaded discs in series that permits one-way flow and gives a higher level of backflow protection than a single check. It is tested by observing differential pressure across the discs.

The main vertical pipe that carries soil from water closets down to the drain. It must be vented, supported and fitted with a rest bend at the base to control flow.

A vertical pipe carrying discharges from sinks, basins and baths, separate from or combined with the soil stack. Correct sizing and venting prevent trap seal loss.

A pipe connecting a drainage system to open air, equalising pressure so water seals stay intact. It also releases sewer gases safely above roof level.

A one-way valve that admits air into a drainage system when pressure drops but closes to stop foul air escaping. It can replace a vent pipe where a roof penetration is impractical.

The depth of water held in a trap, typically 50 mm, that blocks sewer gas from entering a building. It is lost by siphonage, evaporation or pressure imbalance, so venting matters.

A U-shaped fitting below a fixture that holds a water seal and discharges to the waste pipe. It must be accessible for cleaning and correctly sized for the fixture it serves.

Loss of a trap seal caused by pressure changes when another fixture discharges nearby. It is prevented by correct venting, adequate pipe sizing and limiting the number of fixtures per branch.

A bend with a long radius and a supporting foot, fitted at the bottom of a soil stack to turn flow into the drain. It reduces turbulence and erosion at the base of the stack.

An access point in a drain run, with a removable cover, where the drain can be rodded or inspected. It is placed at changes of direction, junctions and intervals on long runs.

A trapped fitting that receives surface water or waste from outside and connects it to the drain. The trap stops smells escaping while still letting water away.

A chemical paste or liquid applied to cleaned metal before soldering that removes oxide and helps molten solder flow. Residue must be wiped off afterwards because it is corrosive.

A joint where solder is drawn by capillary action into the small gap between pipe and fitting. Both surfaces must be clean, fluxed and evenly heated for a sound joint.

A filler metal melted to join pipes at a temperature below the melting point of the parent metal. Lead-free solder is now standard on potable water systems.

Joining metals with a filler that melts above 450 degrees Celsius but below the melting point of the parts. It gives stronger joints than soldering and suits higher temperatures and pressures.

A mechanical joint where a nut tightens an olive onto the pipe to seal it. It needs no heat, but the pipe end must be cut square and fully inserted to avoid leaks.

A joint where a pipe pushes into a fitting and is gripped by an internal ring and sealed by an O-ring. Fast to install, but the pipe must be cut clean and inserted to the marked depth.

A thin tape wrapped around male threads to seal screwed joints. It is wound in the direction of thread travel so it is not unwound as the fitting is tightened.

An adjustable wrench with serrated jaws that grip round pipe for turning or holding. Correct jaw direction and steady pressure avoid crushing or marking the pipe.

Removing the sharp inner and outer edge left after cutting a pipe. Burrs restrict flow and can damage seals in push-fit and compression joints, so they must be reamed out.

A valve that shuts off water to a section, fixture or appliance for repair. Labelling and testing isolation valves keeps maintenance safe and limits water damage.

The main isolating valve controlling water entry to a property, usually with a screw-down head. It must be accessible and known to occupants so supply can be cut in an emergency.

A device that measures the volume of water passing into a property for billing and leak checks. A meter creeping with all taps closed indicates a hidden leak.

Finding the source of escaping water using observation, meter checks, pressure testing and acoustic or moisture instruments. Early detection limits structural damage and water waste.

A priced schedule listing measured quantities of materials and work for a project. It lets contractors price consistently and forms the basis for progress payments and variations.

The process of measuring quantities of pipe, fittings and fixtures from drawings to prepare an estimate or order. Accurate take-off reduces waste and avoids site delays.

An allowance added to an estimate for unforeseen work, price changes or site problems. It is not profit; it covers risk and is drawn down only when needed.

The order of risk-reduction measures: eliminate, substitute, engineer controls, administrate, then use PPE last. It guides safe decisions rather than relying on protective equipment alone.

Clothing and gear such as gloves, goggles, boots and helmets worn to reduce injury. It is the last line of defence and must fit, be maintained and be used with other controls.

An enclosed area with restricted entry and poor natural ventilation, such as a pit or tank, where gases can build up. Entry requires assessment, testing, a permit and a standby person.

A written authorisation setting out the hazards, controls and time limits for high-risk tasks. It ensures checks are done and the area is made safe before and after the job.

Switching off and physically locking an energy source, such as power or water, before work begins. A tag and lock prevent accidental reconnection while someone is working on the system.

Lifting and moving loads using the legs, a straight back and a close hold, or using aids for heavy items. Assessing the load first prevents back and crush injuries on site.

Using the least water needed through low-flow fixtures, leak repair, metering and reuse. It lowers bills, reduces energy for heating and eases pressure on supply sources.

Collecting lightly used water from baths, basins and showers for flushing or irrigation after suitable treatment. It cuts mains demand but needs separate pipework and clear labelling.

Separating waste such as metal, plastic, packaging and hazardous residue into correct streams. It improves recycling, meets duty-of-care rules and keeps sites clean and safe.

Identifying a customer need and organising resources, price, risk and service to meet it profitably. In plumbing it covers quoting, cash flow, licensing, insurance and building a reliable reputation.

A fixture that receives human waste and flushes it to the soil pipe through a trap. Correct set-out, flush volume and connection height ensure reliable clearing.

The tank that stores and releases a measured flush to a WC pan, operated by a siphon or valve. Inlet and outlet settings control flush volume and refill level.

A valve outlet that controls water delivery to a basin, sink or bath. Washer, ceramic-disc and cartridge types differ in maintenance and flow control.

An appliance that raises water temperature for domestic use, either stored in a cylinder or heated instantly. It needs a temperature relief valve, safe discharge and correct venting.

A safety valve on a stored hot-water system that opens at a set high temperature to release expanding water. It prevents the cylinder from overheating and rupturing.