YQA Fuel System Controls and Monitoring
10.01 What are the control requirements for duplex pump systems?
Duplex pumps operate so that failure of one pump is monitored and activates the second pump. A secondary aspect of the controls is to alternate operation to test performance and equalize wear on pump units.
The controller monitors the following aspect of the pumps: (a) position of pump selector switch for Not-in-Auto, (b) current sensor for pump On / Off condition, (c) pump motor starter overload condition, (d) pump flow or pressure, (e) pump inlet vacuum and outlet pressure, (f) pump set leak sensor, (g) pump run hours.
Pump controllers can be set for any of the following common operating modes:
Lead / Lag (Primary / Secondary): The lead (primary) pump is selected by the user and the lag (secondary pump operates when a failure of the primary pump is detected.
Alternating: Operates per Lead / Lag (Primary / Secondary) except that the operating pump and lead / lag status alternate on consecutive starts. A variation is to alternate the pumps based on the operating time (hour meter) of the lead pump.
Twin: Both pumps start when there is a fuel requirement.
10.02 What are the control requirements for tank fill systems?
Tank fill controllers provide information on tank levels, monitor high level alarm conditions, and operate actuated valves in tank fill piping that are used for multi-tank selection and high level shutoff. Valve positions are monitored using limit switch inputs to the controller.
Simple controllers will monitor high level switches in the tanks typically 85% high warning, 90% high alarm, and 95% critical high alarm. Level transmitters can also be integrated to provide a gallons or % fill display at the fill station.
Inlet pipe actuated valves are controlled for 2 functions: (a) shutoff on high level, and (b) open valve to allow filling of a single tank on a multi-tank system and confirm closed state of other tank valves.
A typical control sequence would be:
- Less than 85% fill level: allow selection of tank for filling and opening of inlet actuated valve.
- 85% fill level: activate audible and visual alarm
- 90% fill level: activate audible and visual alarm and close inlet valve. Allow short cycle opening of valve upon alarm reset.
- 95% fill level: activate audible and visual alarm and close and disable inlet valve.
10.03 What are the control requirements for day tanks?
The primary function of day tank controls is to operate inlet valves and transfer pumps to refill the day tank as the generator consumes fuel
Typical day tank level switch activations and associated actions are:
- 90% High Level: Activate audible / visual alarm, redundant valve close and pump stop signal, and optional start of high level overflow return pump
- 85% Fill Stop Level: Close inlet valve and stop signal to pumps
- 75% Fill Start Level: Open inlet valve and send signal to pumps for start
- 50% Low Level: Activate audible / visual alarm, redundant open inlet valve and signal to pump start, activate secondary valve and secondary pump
- 15% Critical Low Level: Activate audible / visual alarm, signal to generator controls for optional generator shutdown
Leak Sensor: Activate audible / visual alarm, disable valve open and pump start signals
Other day tank control functions are: (a) monitor controller for Not-in-Auto status, (b) monitor optional level transmitter and display tank volume in gallons, inches and % fill, Monitor optional temperature transmitter and display tank temperature, (d) operate high level overflow pump for temperature control functions, (e) provide system status information to BMS systems.
10.04 What are the control requirements for multi-tank selection?
Large fuel systems use multiple tanks for several reasons: (a) to provide redundancy against a single tank failure, (b) to provide total fuel volumes in excess of maximum commercially available tank sizes, (c) to provide total required fuel volumes where space limitations set the single tank maximum volume, or (d) to provide total required fuel volumes where regulatory limitations set the single tank maximum volume.
Tank selection controls are required for several purposes: (a) to fill multiple tanks safely from a common fill station, (b) to allow supply of generator fuel from one tank, and safely return fuel to that same tank, and (c) to allow filtration of one tank with return of fuel to that same tank
Tank Fill Control:
The fill station controller monitor high level sensors in the tank at 85%, 90% and 95% fill. Inlet pipe actuated valves are controlled for 2 functions: (a) shutoff on high level, and (b) open valve to allow filling of a single tank on a multi-tank system and confirm closed state of other tank valves. Inlet valve positions are monitored by limit switch inputs to the controller.
Generator Fuel Supply:
Facility operators want to manually select the lead supply tank in the system to manage fuel levels and even the operating time for equipment. One tank may be operated until its level is reduced to allow for receipt of a full truckload of fuel to maximize purchasing efficiency.
The control system will automatically switch to a tank for fuel supply if (a) the primary supply tank is in low level, or (b) the primary tank dedicated pumps or valves are in a fail condition.
When a tank with submersible pumps is selected, its pumps are activated when the day tanks require fuel. When suction pumps are used, the controller opens an actuated valve in the suction pipe, and confirms that the valves in the other tank suction piping is closed.
A critical aspect of the control is that the tank selected for fuel supply is required to receive any return flow or overflow fuel. This occurs by opening the return flow pipe actuated valve (or directing a return flow 3-way valve) for the selected tank and confirming the closed position of the return flow valve at other tanks.
Filtration functions are the same as the characteristics of selecting a tank for generator fuel supply. An important difference is the risk associated with failure to properly control return flow valve positions. Since filter transfer pumps operate for relatively long durations – and typically automatically, a small transfer rate between tanks can proceed un-noticed until a tank overfill condition occurs.
For this reason it is critical that tank high level sensors are monitored and disable the filtration system on a high level condition.
Note that actuated ball valves are recommended for tank selection systems for generator fuel supply and filtration systems. Actuated butterfly valves or ball valves are used for tank fill systems. Solenoid valves are not recommended because of their tendency to leak fuel through the valve when the seat is damaged, deteriorates with age, or sealing is compromised by particulates.
10.05 What are the control requirements for filtration / polishing systems?
Control panels include monitoring functions for the filter and pump operation, and the operator interface for selecting operating modes and timer cycles.
Filtration / Polishing units are designed to accommodate a variety of operating modes:
- (a) continuous operation
- (b) manual operation start with auto stop based on programmable cycle time
- (c ) automatic repeating operation based on a programmable ON and OFF cycle time.
- (d) automatic repeating operation based on day-time start and ON cycle time
- (e) manual operation start with auto stop based on programmable filtered volume
- (f) automatic repeating operation based on day-time start and programmable filtered volume.
Controllers also monitor the operating performance of the systems including (a) pump current sensors, (b) pump overload status, (c) filter assembly leak detection, (d) filter water accumulation, (e) filter differential pressure.
10.06 What are typical points monitored by the fuel system controls?
Fuel system controllers monitor a wide range of operating characteristics and provide this information to building management systems. Here are some of the typical points monitored:
Bulk Tanks: Volume (Gallons), Temperature compensated volume, ullage – empty space in tank, temperature, tank leak status, sump leak status, pipe leak status.
Fuel Pumps: On / Off status, Manual- Off-Auto status, motor starter overload status, pump current sensor, duplex pump assembly leak detection, pump hours, pump flow rate, pump fail, lead – lag status
Day Tanks: High level. low level, critical low level , leak, fill active
Tank Selection: Tank Active, fuel supply valve position, fuel return valve position, high tank level, low tank level.
Filtration: Active status, filter assembly leak, pump fail, water alarm, differential pressure alarm, pump hours, filter gallons.
10.07 How are tank monitors such as Veeder Root integrated into fuel system controls?
Tank monitors are integrated into fuel system controls by 2 methods: (a) output relays for tank conditions, and (b) through a serial interface – ASCII via RS-232 or Ethernet.
Typical output relay functions are: high level, low level, tank leak, sump leak, pipe leak.
Typical serial information is: tank volume, temperature compensated volume, ullage – space available in tank, and temperature.
10.08 What are the building control interfaces are most common?
Controllers interface with Building Management Systems through a variety of protocols based on the preference of the BMS brand or a facility standard. These protocols include Modbus, BACnet, Metasys N2, and LON.
The major building management systems will integrate using any or all of these protocols. The major systems include: Siemens, Johnson Control, TAC, Honeywell, Automated Logic, and Allerton
10.09 What is the typical interface with generator controls?
Generator controls may require information from day tank systems, typically: day tank high level, low level, critical low level, and leak. The generator may use the critical low level signal for a shutdown of the generator.
These signals are typically provided as dry contact outputs from the day tank controller.
10.10 What is the typical interface with switchgear controls such as ASCO and Russelectric?
Switchgear controls may also require inputs from the fuel system equipment typically: main tank low level, main tank leak, day tank high level – low level – leak.
These signals are typically provided as dry contact outputs from the day ta