8
7. Discharge arrangement.
The T&P valve may be discharged vertically into the tundish, with the pressure relief valve T’d in from
the side (see Fig 7.1 below). The Tundish must be installed in a position so that it is clearly visible by
the user. In addition, the discharge pipe from the Tundish should terminate in a safe place where
there is no risk to persons in the vicinity of the discharge, be of metal and:
Fig 7.1
(a) Be at least one pipe size larger than the normal outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of a straight pipe 9m long, i.e. discharge pipes between
9m and 18m equivalent resistance length should be at least two sizes larger then the normal outlet
size of the safety device, between 18m and 27m at least three sizes larger and so on. Bends must be
taken into account in calculating the flow resistance. Refer to the diagram, tables and worked
example detailed in Fig 7.3.
(b) Have a vertical section of pipe at least 300mm long below the Tundish before any elbows or bends
in the Pipework.
(c) Be installed with a continuous fall.
(d) Have discharges visible at both Tundish and the final point of discharge, but where this is not
possible or practically difficult,
there should be clear visibility at one or other of these locations.
Examples of acceptable discharge arrangements are:
-
Ideally below a fixed grating and above the water seal in a trapped gully.
-
Downward discharge at low level, i.e. up to 100mm above external surfaces such as car
parks, hard standings, grassed areas, etc. providing that where children play or otherwise
come into contact with discharges, a wire cage or similar guard is positioned to prevent
contact whilst maintaining visibility.
-
Discharge at high level, e.g. into a metal hopper and metal down pipe with the end of the
discharge pipe clearly visible (Tundish visible or not) or onto a roof capable of withstanding
high temperature discharges of water and being 3m from any plastic guttering system that
would collect such discharges.
-
Where a single pipe serves a number of discharges such as in blocks of flats, the number
served should be limited to not more than six systems so that any installation discharging
can be traced reasonably easily. The single common discharge pipe should be at least
one pipe size larger than the largest individual discharge pipe to be connected. If unvented
hot water stored systems are installed where discharges from safety devices may not be
apparent i.e. in dwellings occupied by blind, or disabled people, consideration should be
given to the installation of an electrically operated device to warn when discharge takes
place.
T&P Valve
Pressure
Relief Valve
15mm
15mm
15mm
22mm
Tundish