Sequence Of Operation; Important Notes - Siemens LMV5 Series Technical Instructions

Technical Instructions
Document No. LV5-8000
Valve Proving with Two Pressure Switches (continued)

Sequence of Operation

1. The blower energizes, but nothing happens as CR1 remains open.
2. V2 opens, evacuating the space between the main valves.
a. The V2 POC switch changes state, but this has no effect on CR1.
3. V2 closes, and the waiting time begins.
a. If V1 leaks by, the low SP switch will open (NO), and the valve proving input will de-
energize (test fail).
b. The high SP switch is essentially not in the circuit at this point (CR1 open)
4. If V1 passes the test, V1 is opened, pressurizing the space between the main valves.
a. Normally open contact (4) on the V1 POC switch latches CR1 coil, all CR1 contacts
change state.
b. The high SP switch will be open (NO). The low SP switch is essentially removed from the
circuit.
5. V1 closes, and the waiting time begins.
a. If V2 leaks by, the high SP switch will close and the valve proving input will energize (test
fail).
b. CR1 coil is still latched at this point.
6. The burner lights off, V1 and V2 are energized, both POC switches open.
a. This has no effect on the CR1 coil, which remains latched.
7. After post purge, the blower output de-energizes and un-latches the circuit.

Important Notes

1. The valve proving input X9-03.2 must be energized for the V1 leak test, and de-energized for the
V2 leak test.
2. Valve proving must be done on startup only.
3. If the relay were to fail (stick one way or the other), a less-sensitive valve proving test would
result. A POC switch could never be jumpered by a failed relay.
Appendix A Page 36
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