24
Sealed system requirements
See
Fig. 1.35
A.
The installation must comply with the regulations in
force. Maximum water 82ºC temperature.
B.
An approved safety valve set to operate at 3 bar (44 Ibf/
In2) shall be fitted in the flow pipe close to the boiler.
There must not be any valve between the safety valve
and the boiler. The valve should be positioned on a
discharge pipe fitted to prevent any discharge or creating
a hazard to occupants or cause damage to electrical
components and wiring.
C.
An approved pressure gauge covering at least the range
0 to 4 bar (0 to 60 Ibf/In2) shall be fitted in the system, in a
visible position.
D.
An approved diaphragm type expansion vessel, shall be
connected at a point in the flow pipe close to the boiler.
The vessel must be chosen to suit the volume of the
water in the cistern and the system charge must not be
less than the static head at the point of connection.
Safety Valve
Setting
3.0 bar
Vessel charge
and initial
system
pressure
0.5 bar
1.0 bar
Multiplying
Factor
0.09
0.16
Expansion
Vessel volume
(litres) =
System volume
Vs x factor
L
Vs x
0.0833
L
Vs x
0.109
Vs = System Volume Litres
Sealed System
E.
The hot water cylinder shall be either the direct coil type
or a cylinder fitted with a calorifer which is suitable for
the system pressure.
F. The Make-Up Vessel
Provision shall be made for
replacing the lost water from the system by either of the
following methods:
a.
From a make-up vessel or tank, and connected
through a non-return valve to the system on the
return side of the hot water cylinder or return side of
all heat emitters or radiators.
b.
Where access to a make-up vessel would be difficult,
by a remote automatic pressurisation and make-up
unit.
c. Mains Connection
There shall be no connection to
mains water supply or to the water storage cistern
supplying domestic hot water, even though a non-
return valve may be fitted, without the approval of
the local water authority.
d. The Filling Point
The system shall be fitted with a
filling point at a low level, and be used in accordance
with the local water authority requirement.
e. Commissioning - General
The system shall be filled
by water by a method acceptable to the Local Water
Authority.
Check the operation of the safety valve manually. After
flushing and refilling the system either:-
•
(a) If a make-up vessel is filled release water from the
safety valve until the level in the make-up bottle falls
visibly, then top up the make-up bottle.
•
(b) If there is no make-up vessel either release or
introduce water until the designed cold water pressure
level is reached.
Commissioning
Follow the commissioning instructions as for open vented
systems. See section Commissioning Instructions with the
following additions:-
Fill the system until the pressure gauge registers 1.5 bar
(22Ibf/In2). Clear any airlocks and check for water soundness.
Check the operation of the safety valve, by allowing the
water pressure to rise until the valve opens. The valve should
open within ±0.3 bar (±4.35 Ibf/In2) of the pre-set pressure, if
this is not possible conduct a manual check and test.
Release water from the system until the minimum system
design pressure is reached 1.0 bar if the system is to be pre-
pressurised.
Any set pointer gauge should be set to coincide with the
recommended filling pressure.
