4
EN2R--9023 9705R0--NE
DESCRIPTION
The A4021 valve proving system checks the effective closure
of the valves
before
burner start--up (pre--configuration) or
at
the end of
a heat demand (post--configuration). The
configuration can be set by means of wiring the A4021 in two
different ways, see Fig. 2. and 3.
The flow chart (Fig. 5. ) and sequence diagram (Fig. 6. )
explain the procedure during the valve proving.
An external pressure switch monitors the pressure between
both valves. The pressure switch must be set to half the inlet
pressure in order to test both valves with the same sensitivity.
After a short interruption of the mains supply during valve
proving or during RUN, the A4021 restarts automatically.
The A4021 valve proving system can be used with several
pilot--valve configurations, like intermittent and interrupted
pilot systems and 3--valve configurations as well.
14
9
L
12
A4021
ignition
controller
H.D
LGPS
Fig. 2. Valve proving
pre--configuration
.
14
9
L
12
A4021
ignition
controller
LGPS
H.D
Fig. 3. Valve proving
post--configuration
.
V1
V2
heat
demand
burner
Pinlet
Pinlet
2
L.G.P.S.
G.P.S.
gas
air
Servo Motor MT4000 Series
Combi--valve VQ400 Series
Valve Proving System
A4021 Series
burner--controller
7800 SERIES
Gas pressure switches
C6058A Series
Fig. 4. System set--up .
Working principle
The A4021 valve proving system is based on the pressure
status--principle. This means that the valves are checked by
means of measuring (on/off) the pressure in the gas--pipe
between the two safety--valves. This system will only work
when there is sufficient gas--pressure (line--pressure).
Therefore a Low Gas Pressure Switch (LGPS) is part of the
installation. When the line--pressure (Pinlet) is too low the
LGPS will disable the valve proving system.
The section between the two valves is filled with gas
(high--pressure status) by opening valve--1 (upstream valve)
and the pipe is emptied (low--pressure status) by closing
valve--1 and opening valve--2 (down--stream). When one of
the valves is leaking this will mean that either the pressure
will not maintain the high--pressure status or the low--pressure
status at the end of the test period.
For this method of testing, the test time is a function of three
parameters.
−
inlet pressure
−
volume between the valves.
−
maximum burner capacity.
The test time can be calculated as given on page11. Different
test times are available by different O.S. numbers.