Worked Example; Draining The Appliance - Ariston PRO1 ECO Series Manual

If unvented hot water storage systems are installed where discharges from safety
devices may not be apparent i.e. in dwellings occupied by the blind, infirm or disabled
people, consideration should be given to the installation of an electronically operated
device to warn when discharge takes place. Note: The discharge will consist of
scalding water and steam. Asphalt, roofing felt and non-metallic rainwater goods may
operated device to warn 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.
be damaged by such discharges.
Table 2
Sizing of copper discharge pipe "D2" for common temperature valve outlets.
Valve outlet size
G 1/2
G 3/4
G 1

Worked example

The example below is for a G 1/2" temperature & pressure relief valve with a
Worked example
discharge pipe (D2) having 4 no. elbows and length of 7 m from the tundish to the
The example below is for a G 1/2" temperature & pressure relief valve with a discharge pipe (D2) having 4 no. elbows and
point of discharge.
length of 7 m from the tundish to the point of discharge.
From Table 2
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
Maximum resistance allowed for a straight length of 22 mm copper discharge pipe
to: 5.8 m.
(D2) from G 1/2" T & P valve is 9 m.
As 5.8 m is less than the actual length of 7 m therefore calculate the next
Subtract the resistance for 4 no. 22 mm elbows at 0.8 m each = 3.2 m.
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.
Therefore the maximum permitted length equates to: 5.8 m.
Subtract the resistance for 4 no. 28 mm elbow at 1.0 m each = 4 m. Therefore the maximum permitted length equates
As 5.8 m is less than the actual length of 7 m therefore calculate the next
to: 14 m
largest size.
As the actual length is 7 m, a 28 mm (D2) copper pipe will be satisfactory.
Maximum resistance allowed for a straight length of 28 mm pipe (D2) from G 1/2" T
& P valve equates to: 18 m.

Draining the appliance

Subtract the resistance for 4 no. 28 mm elbow at 1.0 m each = 4 m.
The appliance must be drained if left inactive in a room subject to frost and/or in the event of prolonged inactivity.
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.
Typical drain arrangement and system designs will vary:
1. Turn power off to ensure appliance is not operated when empty.
2. Turn off cold supply to appliance.
3. Shut off hot water feed from appliance.
16
4. Connect hose to drain cock and place other end in sink, basin etc.
5. Open drain cock and open TPR valve to vent cylinder.
Minimum size of
discharge pipe D1*
15 mm
22 mm
28 mm
Minimum size of
discharge pipe D2*
from tundish
22 mm
28 mm
35 mm
28 mm
35 mm
42 mm
35 mm
42 mm
54 mm
Maximum
resistance allowed,
expressed as a
length of pipe (i.e.
no elbow or bends)
Up to 9 m
Up to 18 m
Up to 27 m
Up to 9 m
Up to 18 m
Up to 27 m
Up to 9 m
Up to 18 m
Up to 27 m
Resistance created
by each elbow or
bend
0.8 m
1.0 m
1.4 m
1.0 m
1.4 m
1.7 m
1.4 m
1.7 m
2.3 m