4.9 tUndiSH
A suitable tundish is supplied with the cylinder for fitting in the
common discharge pipe from the T&P and Expansion relief
valves. On the pre-plumbed cylinders this is factory-fitted on the
secondary circuit pipework. On the standard cylinders this is
supplied loose and must be fitted by the installer.
! WArninG !
the tundish must not be positioned above or in close
proximity of any electrical current carrying devices or
wiring.
A discharge pipe must be fitted to the outlet of the tundish. This
must conform to the requirements as given in Section 4.9 of these
Installation and User Instructions.
4.10 diScHArGE PiPE
1. 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:
a) Be at least one pipe size larger than the normal outlet
size of the safety device unless its total equipment
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 larger
than the normal outlet size of the safety device, between
18m and 27m at least three sizes larger and so on.
Bends must be taken in to account in calculating the
flow resistance. Refer to sections 4.10, 4.11 and 4.12.
b) Have a vertical section of pipe at least 300 mm long,
below the tundish before any elbows or bends in the
pipe work.
c)
Be installed with a continuous fall of 1:40 (2.5°).
d) Have discharges visible at both the 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.
2. Examples of acceptance discharge arrangements are:
a)
ideally below a fixed grating and above the water seal in
a trapped gully.
b) downward discharges at a low level; i.e. up to 100mm
above external surfaces such as car parks, hard
standings, grassed areas etc. are acceptable providing
that where children may play or otherwise come in to
contact with discharges, a wire cage or similar guard
is positioned to prevent contact, whilst maintaining
visibility.
c) discharges at high level; e.g. in to 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 3m from any plastics guttering systems that
would collect such discharges (tundish visible).
3. 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 6 systems so that any installation 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 storage systems are installed where
discharges from safety devices may not be apparent i.e.
in dwellings occupied by blind, infirm or disabled people,
consideration should be given to the installation of an
electronically operated device to warm when discharge takes
place.
! notE
!
the discharge will consist of scalding water and steam.
Asphalt, roofing felt and non-metallic rainwater goods may
be damaged by such discharges.
4.11 diScHArGE PiPE
ArrAnGEmEnt
Safety device ( e.g.
temperature relief valve)
Metal
discharge
pipe from
temperature
Metal discharge pipe from tundish
with continuous fall. See table and
worked example on next page
discharged below
fixed grating
Fixed grating
Trapped gully
Tundish
600mm max
300mm
min
figure 4-2:
Typical discharge pipe arrangement
Section 4: Secondary circuit installation
Page 16
