Worked example
The example below is for a G 1/2” temperature & pressure relief valve with
a discharge pipe (D2) having 4 no. elbows and length of 7 m from the
tundish to the point of discharge.
From Table 2
Maximum resistance allowed for a straight length of 22 mm copper
discharge pipe (D2) from G 1/2” T & P valve is 9 m.
Subtract the resistance for 4 no. 22 mm elbows at 0.8 m each = 3.2 m.
Therefore the maximum permitted length equates to: 5.8 m.
As 5.8 m is less than the actual length of 7 m therefore calculate the next
largest size.
Maximum resistance allowed for a straight length of 28 mm pipe (D2) from
G 1/2” T & P valve equates to: 18 m.
Subtract the resistance for 4 no. 28 mm elbow at 1.0 m each = 4 m.
Therefore the maximum permitted length equates to: 14 m
As the actual length is 7 m, a 28 mm (D2) copper pipe will be satisfactory.
d) ELECTRICAL
WARNING:
The appliance must be earthed
The electrical installation must be in line with the current I.E.E. wiring
regulations.
A mains supply of 240 VAC 3 kW (13 amps) is required
(Fig. 5 & 6)
Heat resisting cable, round 3 core 1.5 mm (to BS 6141 table 8) should be
used to connect to the electrical supply through either:
- a 13 amp socket to BS 1363; or
- a double pole fused isolating switch with a contact separation of 3 mm
minimum on each pole.
The cable enters the terminal compartment through a tube embedded in
8
Valve outlet size
Minimum size of
discharge pipe D1*
Minimum size of
discharge pipe D2*
from tundish
Maximum
resistance allowed,
expressed as a
length of pipe (i.e.
no elbow or bends)
Resistance created
by each elbow or
bend
G 1/2
15 mm
22 mm
28 mm
35 mm
Up to 9 m
Up to 18 m
Up to 27 m
0.8 m
1.0 m
1.4 m
G 3/4
22 mm
28 mm
35 mm
42 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.0 m
1.4 m
1.7 m
G 1
28 mm
35 mm
42 mm
54 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.4 m
1.7 m
2.3 m
Table 2
Sizing of copper discharge pipe “D2” for common temperature valve outlets.
