I am trying to assist a customer with evaluation of their current process fluid heater controls systems.
In evaluation of their existing system, we identified that there is currently a relay controlled Pilot Valve hold initiated in the scheme when the system is started up before initiating product flow.
During this Pilot Valve hold, the existing system maintains the pilot on without closing both of the Main Gas safety valves. There is some concern with this setup and questions regarding allowability in the NFPA code.
We are trying to determine if there is a requirement for both Main Gas safety shutoff valves to close during a PV hold.
There are a few conditions which will send the heater back to pilot instead of tripping it completely, but we want to make sure that the method being used to hold the pilot is correct.
The existing BMS is a Fireye EP160 with a CompactLogix PLC used for CCS.