Potterton envoy 30, Installation & Service Instructions Manual

Page: 9 / 36

9
THE SYSTEM – Page 9
EXPANSION VESSEL
A diaphragm type expansion vessel to BS.4814 Part 1
shall be fitted close to the inlet side of the pump. The
connecting pipework should not be less than 15mm
(1/2in nominal). Pipework connecting the expansion
vessel should not incorporate valves of any sort.
Methods of supporting the vessel are supplied by the
manufacturer. The nitrogen or air charge pressure of
the expansion vessel shall not be less than the
hydrostatic head (height of the top point of the system
above the expansion vessel). To size the expansion
vessel it is first necessary to calculate the volume of
water in the system in litres. The following volumes may
be used as a conservative guide to calculating the
system volume.
CYLINDER
The hot water cylinder must be an indirect coil type or a
direct cylinder fitted with an emersion calorifier suitable for
operating at a gauge pressure of 0.3 bar (Slbf/in
2
) in
excess of safety valve setting. Single feed indirect
cylinders are not suitable for sealed systems.
METHOD OF MAKE-UP
Provision shall be made for replacing water loss from the
system either:-
i) from a make-up vessel or tank mounted in a position
higher than the top point of the system, and
connected through a non-return valve to the system
Boiler Heat Exchanger 2.4 litres on the return side of hot water cylinder or the return
Small Bore Pipework 1 litre per kW of system side of all heat emitters.
output or
Micro Bore Pipework 7 litres
Steel Panel Radiators 8 litres per kW of system -
output ii) where access to make-up vessel would be difficult by
using the mains top up method or a
Low Water Capacity - 2 litres per kW of system - remote automatic pressurisation and make-up unit
Radiators output as illustrated in FIG. 5, Methods 1 and 2.
Hot Water Cylinder 2 litres
If the system is extended, the expansion vessel volume
may have to be increased unless previous provision
has been made for the extension. Where a vessel of the
calculated size is not available, the next available larger
size should be used.
The boiler flow temperature is controlled at
approximately 82
0
C MAX.
The vessel size can now be determined from the
following table where V=System volume in litres.
MAINS CONNECTION
There shall be no connection to the mains water supply or
to the water storage tank which supplies domestic water
even through a non-return valve, without the approval of
the local Water Authority.
FILLING POINT
The system shall be fitted with a low filling point at low
level which incorporates a stop valve to BS.1010 and a
double check valve (approved by the National Water
Council) to be fitted in this order from the system mains,
refer to FIG. 5, Method 1.
Vessel Charge Pressure (Bar) 0.5 1.0
Initial System Pressure (Bar) 1.0 1.0
Expansion Vessel Volume Litres V x 0.11 V x 0.087