Generator Diesel Fuel Day Tank-Application Guidelines and Important Considerations

The day tank is a fuel containment system designed to be installed in the immediate vicinity of the engine to provide a reliable supply of diesel fuel. These are often required if the fuel pump mounted on the engine is unable to draw fuel from the remotely mounted fuel tank due to distance or altitude issues. For safety and reliability, these fuel systems are configured as suction type. That is, the day tank draws fuel from the main tank and the engine draws fuel from the day tank.

There are significant differences in the configuration of these systems when used in ground storage tanks (AST) or underground storage tanks (UST). There are also important considerations related to tank accessories.

Integration with AST-For this type of application, attention should be paid to the height of the day tank relative to the main AST. Certain components must be installed in the fuel tubing as siphons can occur between the day tank and the AST. Solenoid valves and strainers are usually mounted at the pump inlet of the tank. This is an electric valve that normally closes. Opens only when a low tank level is detected. At that point, the solenoid valve opens and the supply pump turns on. When the tank reaches full level, the solenoid valve and pump are turned off, the fuel flow is stopped and the fuel inlet to the tank is closed. The recommended additional components in these systems are a manually operated ball valve and a fusible link valve that automatically closes in the event of a fire. These should be installed at the inlet and outlet of the tank so that the equipment can be isolated for emergency or regular maintenance purposes.

A well-designed system requires the day tank to be able to return excess fuel to the AST. If you do not stop the filling pump or close the solenoid valve, the tank may continue to fill. A spill is inevitable without a means of returning excess fuel. The overflow return pump is usually mounted on the tank and should be sized to overcome the supply pump. The outlet must be equipped with a check valve to prevent reverse power flow when the return pump is stopped.

For some applications, the AST is remote and too far for the day tank pump to reliably draw fuel. In such cases, the day tank is equipped with an overflow pump and a stand-alone supply pump is installed near the main tank to draw fuel from the AST and push it into the day tank. The remote pump connects to the tank level controller to receive start / stop signals.

Integration with UST-For this type of application, you need to consider the potential for day tank feed pumps to lose prime. For this reason, it is common to install a foot valve in the main tank and a hand pump, check valve, and solenoid valve in the day tank. The hand pump allows for emergency filling and also provides a means to restore the fuel prime of the line supplying the electric pump. Check valves and solenoid valves work to limit backflow to the main UST. In UST applications, overflow (return) fuel is typically piped from the day tank to the UST, and gravity is sufficient to prevent the day tank from overflowing. As with the AST design, if the day tank is too far from the UST, the supply pump should be located near the UST.

General Configuration Recommendations-The following are additional recommendations to consider for a well-configured system.

1. Claims UL508 compliant control as well as UL142 compliant day tanks.

2. Adjust the size of the tank to ensure a minimum of 2 hours of engine running time without refilling.

3. The supply pump should be three times the full load fuel consumption of the engine (or engine if the tank supplies multiple engines). In the above example (120GPH or 2GPM consumption), the pump size should be at least 6GPM.

4. The return pump (if applicable) must be sized to exceed the capacity of the supply pump.

5. Make all accessories (ball valves, solenoid valves, etc.) larger than the fuel line that connects them.

6. Specify a double wall structure with a rupture basin leak detection sensor. This sensor is interconnected to the supply pump and stops its operation in the event of a leak in the main containment. The controller should also indicate the status with a visual alarm.

7. Always specify that the tank contains a suitable pressure relief valve cap. These allow for emergency vents if normal atmospheric vents are blocked. For internal installation, the work vent must be plumbed externally.

8. Check with the competent municipality (AHJ) to see if the controller and accessories need to get power from the engine battery (such as 24Vdc), or if the 120Vac emergency accessories circuit is acceptable. Understand.

9. Most diesel engines consume more fuel than they need to burn. Excess fuel is usually returned to the day tank. Depending on the fuel return rate, you may need to consider routing to the main tank, or you may need to design your system with a larger day tank or fuel cooler to avoid overheating the new fuel supply. in some cases. The heated fuel reduces the engine’s horsepower rating and can cause the engine to shut down if the building load exceeds the engine’s power capacity.

10. For prime duty applications, specify a dual fuel supply pump set with a cast iron pump housing and steel rotor to increase system reliability. Duplex pumps allow lead / lag or simultaneous operation at the operator’s discretion. The more robust cast iron pumps last longer and have less operating noise.

11. Claim the following local and remote alarms from the vendor.

a) Low level alarm and remote announcement output contacts.

b) High level alarm and remote announcement output contacts.

c) Critical high level alarms, pump shutdowns, and remote notification output contacts.

d) Critical low level alarms, engine shutdown (prevents fuel prime loss), and remote announcement output contacts.

e) Tank leak detection alarm and remote announcement output contacts.

The above guidelines may help you choose the right product for your application. However, it is advisable to contact the vendor to find out which options and accessories may be needed to ensure reliable and safe operation of a particular fuel system application. For additional resources related to day tanks and related fuel systems, please visit: http://www.hurtado.cc/resources.htm..