RETURN. A safety valve is specified for the primary flow to ensure discharge path
at all times in the event the feed/vent connection is isolated from the boiler flow
[see 3.7.2(i)]. However, in the event the system is configured with no isolation
valve on the primary flow and wired such the boiler cannot fire when all zone
valves are closed, then the safety valve may be omitted. Note that the minimum
static head required is 9 ft at the top of the boiler.
Although suitable for open vented systems with combined feed and vent
arrangements, the Q37 are low water content boilers. As such, any air
entrainment within the system water will produce boiler “kettling”. It is therefore
recommended, if in any doubt, to consider the use of sealed systems where
possible.
3.7.2
Sealed Systems
Sealed systems must be designed in accordance with BS 5449 and BS 7074 Pt1.
A typical sealed system is shown in Figure 2.7.2. It must include :
(i)
A safety valve fitted on the flow, adjacent to the boiler. It must be non
adjustable and preset to 3 bar. A drain pipe must be attached, at least as
big as the valve connection, and routed to drain in any area not
hazardous nor where it may be subject to freezing.
(ii)
An expansion vessel complying with BS 4814 and sized in accordance
with the requirements of BS 5449 and BS 7074 Pt 1. The vessel must
be positioned on the primary return to the boiler. Table 3.7.2
Expansion Vessel Selection provides guidance for the correct expansion
vessel size to use.
(iii)
A filling point must be fitted, in accordance with local water authority
requirements.
(iv)
A method of system make-up (automatic or manual), in accordance with
local water authority requirements.
WD500
Chapter 3 - Boiler Location
The Keston Q37 & Q37P Boilers
Installation & Servicing Instructions
Page : 14
Keston Q37
Rad. 2
Rad. 1
FLOW
RETURN
By-pass
L/S
Cylinder
Expansion
Tank
Expansion
Pipe
Minimum
9ft Height
28mm
Minimum
Figure 3.7.1 Open Vented System Diagram
Valve
Safety
Valve
