Nu-Way MDFL 3300, Installation And Maintenance Manual

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Valve Proving System
Valve proving systems are standard on all MDFL 3300 and 4000 burners. The standard model fitted
is the Landis & Staefa LDU11. (See page 15)
When the burner operating sequence is initiated the burner control box energises the proving system,
which then carries out the following checks:
The LDU11 control unit is designed to provide automatic gas valve proving (leakage test) based on
the pressure proving principle. The system comprises the control unit, which is fixed to a
bracket/terminal box assembly close to the main valve block, and a dual pressure switch which is
connected to the test space between the main valves. The unit comes pre-wired as part of the gas
train harness.
Gas valve proving is initiated automatically on completion of the burner control circuit prior to burner
start-up. The proving test is based upon the 2-stage pressure proving principal. First, the main
safety valve (V1) on the upstream side of the gas circuit is tested by evacuating the test space (via
the pilot valve V3) and by monitoring the atmospheric pressure in it, then the valves (V2 and V3) on
the burner side are tested by pressurising the test space and monitoring the gas pressure. If the
pressure increases excessively during the first test phase (TEST 1) or decreases excessively during
the second test phase (TEST 2), the control unit inhibits burner start-up and goes to lockout. The
lockout reset button lights up and signals a fault.
A programme indicator, which stops whenever a fault is signalled, indicates which valve(s) set is
leaking.
The control unit requires to be reset manually, either on the unit itself or by a remote resetting if this
has been fitted.
MDFL 3300 & MDFL 4000 Issue 2 08/08 Page 14