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Building Technologies Division
CC1N7696en
20.04.2016
Function
During the first phase of the valve proving test called «Test1», atmospheric pressure
must exist in the length of pipe between the valves to be tested. In plants with a vent pipe
to atmosphere, atmospheric pressure is available if the valve proving test is made prior to
or during the prepurge time. In plants without vent pipe, atmospheric pressure is made
available as the valve proving system opens the valve on the burner side during evacuat-
ing the test space (t4). If the valve proving test LDU11... is performed after burner opera-
tion, the valve on the burner side after the controlled shutdown can be kept open until
evacuating the test space (t4) has elapsed, thus lowering the pressure in the test space
and making certain its gas content is burnt off in the combustion chamber during the
postpurge time. Prerequisite for this procedure is a suitable control program of the burner
control as provided by burner controls type LFE..., LFL..., LGK... or LEC...
The test space is closed off after evacuation. During the first test phase «Test1», which
then follows, the LDU11... checks with the pressure switch if the atmospheric pressure in
the test space is maintained. If the valve on the mains side is leaking, causing the pres-
sure to rise above the switching point of the pressure switch, the LDU11... will trigger an
alarm and initiate lockout. The program indicator then stops to indicate «Test1».
If the pressure does not increase because the valve closes correctly, the LDU11... con-
tinues its program with the second test phase «Test2». For that purpose, the valve on the
mains side is opened during filling the test space (t3) so that the test space is pressurized
(«filling» the test space). During the second test phase – if the valve on the burner side is
leaking – this pressure must not fall below the switching point of the pressure switch. If it
does, the LDU11... will initiate lockout also, thus preventing the burner from starting up.
On successful completion of the second test phase, the LDU11... closes the internal
control loop between terminals 3 and 6 (circuit path: terminal 3 - contact (ar2) - terminals
4 and 5 - contact III - terminal 6). This control loop is normally included in the burner con-
trol’s start control loop.
After the control loop has been closed, the programming mechanism of the LDU11...
returns to its start position to switch itself off. During these so-called idle steps, the posi-
tions of the programming mechanism’s control contacts remain unchanged.
