gledhill GB10 Installation And Servicing Instructions page 16

3.6. SYSTEM / BOILER PUMP
The variable duty pump should be fitted
on the flow pipe from the boiler and have
isolating valves on each side as shown
schematically in diagrams 3.3 and 3.4.
The pressure loss characteristics of the
boilers are shown in diagram 3.9. The
water flow rates and the boiler pressure
o o
losses at 11 C and 20 C temperature
differences are also tabulated below
in table 3.4.
The variable duty pump should be set to
give a temperature difference of no greater
o
than 20 C between boiler flow and return to give
minimum flow rate through the boiler shown
in table 3.4. High resistance micro bore systems
may require a higher duty pump.
3.7. FLOW RATE
If it is necessary to alter the flow rate in a
system, the system can be fitted with a
lockable balancing valve in the main flow or
return pipes. The example is shown as a
valve 'A' in diagram 3.4.
The flow rate through the boiler must not be
allowed to fall below the values given in table
3.2 for the boiler model selected.
3.8. BYPASS VALVE
A bypass is not required on the central heating system unless the system controls could allow the boiler and
the pump to operate when there is no flow.
When a bypass valve has to be fitted, it must be placed at least 1.5 meters away from the boiler as shown
schematically in diagrams 3.3 and 3.4. An automatic bypass valve is recommended.
3.9. DOMESTIC HOT WATER STORAGE CYLINDER
Single feed indirect cylinders are not suitable.
The domestic hot water cylinder must be of the double feed fully indirect coil type. It must be suitable for
working at a gauge pressure of 0.35 bar above the safety valve setting.
When the storage vessel will not have vent to the atmosphere i.e. unvented cylinder is used, then the
installation must comply with the Building regulations and Local Water Company bylaws. See also the
current issues of BS5546 and BS6700.
VER: 02.3 _260505
Supplied By www.heating spares.co Tel. 0161 620 6677
Diagram 3.9 Pressure loss characteristics of the boilers
4.5
4.0
3.5
3.0
2.6 m
2.5
2.0
1.9 m
1.5
1.3 m
1.0
0.8 m
0.5
0.0
0 100 200 300 400 500 600
GB-10
10kW = 430 l/h at 20K dif f
15kW = 640 l/h at 20K diff
Table 3.4 Boiler pressure loss data
Boiler Temperature
Model difference (K)
11
GB30
20
11
GB25
20
11
GB20
20
11
GB15
20
11
GB10
20
GB_10, GB_15
GB_20, GB_25, GB_30
700 800 900 1000 1100 1200
Flow rate (litres/h)
GB-25
25kW = 1070 l/h at 20k diff
GB-15 GB-20
20kW = 850 l/h at 20K diff
Flow rate Pressure loss
(Litres) (m WG)
2342
1288
1951
1073
1561
858
1171
644
780
429
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1300 1400 1500
GB-30:
30kW = 1280 l/h at 20K diff
6.66
2.30
4.79
1.69
3.22
1.17
3.91
1.47
2.00
0.80