Glossary



  • Tap gap

    The vertical distance between the lowest part of a tap outlet and the spillover level of the appliance or receptacle over which the tap discharges. Interpretation given in Regulators’ Backflow Specification - backflow prevention read more

  • Technical Committee

    The WRAS Technical Committee purpose is to advise the WRAS Board on technical issues relating to the interpretation and enforcement of the Water Supply (Water Fittings) Regulations/Scottish Water Byelaws and perform such other functions as the read more

  • Temperature relief valve

    A valve which opens automatically at a specified temperature to discharge fluid Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws read more

  • Terminal fitting

    A water outlet device. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws read more

  • Test code sheets

    A series of performance specifications which collectively form the Regulators’ Specification for Water Fittings. To conform to the Regulators’ Specification for Water Fittings a water fittings must satisfy all of the appropriate read more

  • Trap

    A pipe fitting, or part of a sanitary appliance, that retains liquid to prevent the passage of foul air. Interpretation given in Schedule 2: of the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws read more

  • TSG

    The WRAS Technical Support Groups (TSGs) purpose is: to promote the consistent application of enforcement of the Water Fittings Regulations/Scottish Byelaws by the exchange of information relating to interpretation and application of read more

  • Type AA – air gap

    A non-mechanical backflow prevention arrangement of water fittings where water is discharged through an air gap into a receptacle which has at all times an unrestricted spillover to atmosphere. Maximum permissible fluid category against which a read more

  • Type AB – Air gap

    A non-mechanical backflow prevention arrangement of water fittings complying with Type AA, except that the air gap is the vertical distance from the lowest point of the discharge orifice which discharges into the receptacle, to the critical water read more

  • Type AC - Air gap

    A non-mechanical backflow prevention arrangement of water fittings with a vented, but submerged, inlet; the air gap being measured vertically downwards from the lowest point of the air inlet to the critical level. Maximum permissible fluid read more

  • Type AD - Air gap

    A non-mechanical backflow prevention arrangement of water fittings with a horizontal injector and a physical air gap of 20 millimetres or twice the inlet diameter, whichever is the greater. Maximum permissible fluid category against which a Type read more

  • Type AF - Air gap

    A non-mechanical backflow prevention arrangement of water fittings with an air gap measured downwards from the lowest point of the discharge orifice, which discharges into the receptacle, to the critical level. Maximum permissible fluid category read more

  • Type AG - Air gap

    A non-mechanical backflow prevention arrangement of water fittings with an air gap; together with an overflow, the size of which is determined by measure or a vacuum test. Maximum permissible fluid category against which a Type AG air gap is read more

  • Type AUK1 - Air gap

    A non-mechanical backflow prevention arrangement consisting of a cistern with a Type AG overflow and an air gap; the spill-over level of the receiving vessel (WC pan or other receptacle) being located not less than 300 millimetres below the read more

  • Type AUK2 - Domestic tap gap

    The height of air gap between the lowest part of the outlet of a tap, combination fitting, shower head or other fitting discharging over a domestic sanitary appliance or other receptacle, and the spillover level of that appliance, where a fluid read more

  • Type AUK3 - Higher risk tap gap

    The height of an air gap between the lowest part of the outlet of a tap, combination fitting, shower head or other fitting discharging over any appliance or other receptacle, and the spillover level of that appliance, where a fluid category 4 or 5 read more

  • Type BA - Backflow prevention device

    A verifiable mechanical backflow prevention device consisting of an arrangement of water fittings with three pressure zones with differential obturators and that will operate when potential backflow conditions obtain or there is a malfunction of read more

  • Type CA - Backflow prevention device

    A non-verifiable mechanical backflow prevention device which provides disconnection by venting the intermediate pressure zone of the device to the atmosphere when the difference of pressure between the intermediate zone and the upstream zone is read more

  • Type DA - Backflow prevention device

    A mechanical backflow prevention device with an air inlet which is closed when water within the device is at or above atmospheric pressure but which opens to admit air if a vacuum occurs at the inlet to the device. Maximum permissible fluid read more

  • Type DB - Backflow prevention device

    A mechanical backflow prevention device with an air inlet closed by a moving element when the device is in normal use but which opens and admits air if the water pressure upstream of the device falls to atmospheric pressure, the device being read more

  • Type DC - Pipe interrupter

    A non-mechanical backflow prevention device with a permanent unrestricted air inlet, the device being installed so that the flow of water is in a vertical downward direction. Maximum permissible fluid category against which a Type DC arrangement read more

  • Type DUK1 - Backflow prevention device

    A mechanical backflow prevention device comprising an anti-vacuum valve with a single check valve located upstream. Maximum permissible fluid category against which a Type DUK1 device is accepted as adequate backflow protection: Backflow by read more

  • Type EA - Backflow prevention device

    A verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category against which a Type EA device is accepted as adequate backflow read more

  • Type EB - backflow prevention device

    means a non-verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category against which a Type EB device is accepted as adequate read more

  • Type EC - Backflow prevention device

    A verifiable mechanical backflow prevention device consisting of two verifiable single check valves in series, which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category read more

  • Type ED - Backflow prevention device

    A non-verifiable mechanical backflow prevention device consisting of two single check valves in series, which will permit water to flow from upstream to downstream but not in the reverse direction. Maximum permissible fluid category against read more

  • Type HA - Backflow prevention device

    A mechanical backflow prevention device for fitting to the outlet of a hose union tap and consisting of a single check valve with air inlets that open if the flow of water ceases. Maximum permissible fluid category against which a Type HA device read more

  • Type HC - Backflow prevention devices

    "Type HC - Diverter with automatic return" means a mechanical backflow prevention device used in bath/shower combination tap assemblies which automatically returns the bath outlet open to atmosphere if a vacuum occurs at the inlet to the device. read more

  • Type HUK1- Backflow prevention device

    "Type HUK1 - Hose union tap incorporating a double check valve" means a hose union tap in which a double check valve has been incorporated into either the inlet or outlet of the tap. Interpretation given in Regulators’ Backflow read more

  • Type LA - Backflow prevention device

    An anti-vacuum valve or vacuum breaker, similar to Type DA but suitable for conditions where the water pressure at the outlet of the device under normal conditions of use is greater than atmospheric. Maximum permissible fluid category against read more

  • Type LB - Backflow prevention device

    A mechanical backflow prevention device comprising a Type LA anti-vacuum valve and a single check valve located downstream. Maximum permissible fluid category against which a Type LB device is accepted as adequate backflow protection: Backflow read more