YQA Fuel Transfer Pumps
05.01 What types of pumps are used for fuel transfer?
Fuel transfer pumps are of 3 primary types:
Positive Displacement / Gear Pumps:
- Best Application: Fuel transfer from bulk tanks to generator, filtration polishing systems, generator tank return flow pumps, boiler feed pumps.
- Common Brands are Viking, Blackmer, and Tuthill.
- Benefits: excellent suction characteristics up to about 20 vertical feet, high pressure output capability to several hundred PSI, very low to high flow capacities from 0.25 to several hundred GPM, relatively constant output through range of pressures. Available in full range of voltages and horsepower.
- Limitations: Suction piping characteristics can make starting and keeping prime a problem. Higher flow rate pumps can be relatively higher in cost. Noise and vibration can be relatively higher than alternatives.
- Most Common Problems: Loss of prime in suction piping. Overpressure of discharge piping if improper setting of pressure regulating valves. Debris in pump head if improper strainer.
- Best Application: Transfer to and from delivery vehicles to bulk tanks with flooded suction condition.
- Common Brands are Gorman Rupp and Gould.
- Benefits: High flow rates at relatively low costs.
- Limitations: Limited suction capabilities. Capacity decreases at higher pressures.
- Most Common Problem: Difficulty in self-prime
Submersible Turbine Pumps:
- Best Application: Fuel transfer from underground or aboveground tanks to generator day tanks and boiler feed at limited pressure.
- Common Brands are Red Jacket and FE Petro.
- Benefits: No suction or priming issues. Relatively high flow rates. Relatively low costs.
- Limitations: Pressure limitation of 50 PSI. Not available as 120 VAC. Not available for low flow applications. Not applicable for shallow tanks such as generator base tanks. Headroom required above tank for installation in buildings.
Most Common Problems: Excessive flow rate. Siphon through pump if missing or incorrect anti-siphon
05.02 What accessories are needed for fuel transfer pumps?
- Isolation Valves: Typically manual ball valves to isolate the pump for service.
- Gauges: Typically liquid filled gauges 2.5” to 4” dials both vacuum for pump inlet and pressure for pump outlet.
- Strainers: Inlet strainers to prevent debris in piping system from damaging pump.
- Check Valves: at pump discharge to prevent backflow through pump, or on pump inlet to maintain prime on suction pumps.
- Flex Connectors – Vibration Isolators: to isolate the pump vibration from the piping system.
Pressure Relief / Regulating Valves: To allow flow through pump when downstream valves are closed and prevent overheating of pump body, and for thermal expansion relief in piping.
05.03 How do I determine the required flow rate and pressure?
Here are some quick rules of thumb for determining flow rates and pressures. More precise calculations are often warranted by the requirements of the application, but this is a start.
Flow Rate for Boilers: Take the consumption of all of the boilers at full load. Then multiply by 2 to get the desired flow rate. This will make sure that the pump is fully capable, and helps assure that the last boiler in a series will not be starved for flow.
Pressure at Pump for Boilers: Take the required pressure at the boiler inlet. Add 25% for safety factor. Add 10 PSI for flow loss in piping (and size the piping for a max 10 PSI loss). Add the vertical head from pump to boilers and the suction head from tank to pump. The sum of these will be a good estimate for the required pressure at the pump.
Notes for Boilers: Some boilers and heaters require very low pressure inlets and the challenge to to provide that low pressure. Pressure regulators at the boilers is often a solution, as are head tanks with a continual overflow back to the bulk storage tank.
Flow Rate for Generators: Take the consumption of all generators at full load. Then multiply by 2 to get the desired flow rate. This will make sure that the pump is fully capable, and helps assure that the last generator in a series will not be starved for flow. If the potential for starving day tanks further along in the series is apparent, then flow regulating valves should be used at the day tank inlets to be precise. Also do not oversize the inlet valves.
05.04 How do I determine the pump motor horsepower and voltage?
The required pump horsepower is determined by the requirements for flow rate and pressure (at the pump) by the following equation. Round up to the next standard motor. For non-submersible pumps these would typically be 0.33, 0.50 0.75. 1.00, 1.50, 2.00, 2.50, 3.00, 5.00. For submersible pumps they would be 0.33, 0.75, 1.50, 2.00, 3.00, 5.00.
Pump voltage selection is usually a function of what is readily available in the building. Motors are typically 120 or 208 VAC Single Phase, or 230 or 460 VAC Three Phase. Submersible pumps in the lower HP range are commonly 208 VAC Single Phase, and in higher HP are available either as 208 VAC Single Phase or 480 VAC Three Phase. Many facilities as a rule of thumb will have all motors under 1 HP to be Single Phase and all motors over 1 HP to be Three Phase.
05.05 What maintenance and inspection is required for fuel transfer pumps?
The primary maintenance and inspection requirements for fuel transfer pumps are regular (weekly) inspections for leaks. An annual check of wire terminal tightness is also a recommended practice.
Other than that, the pumps operation is continually checked by the control system for proper operation.
05.06 Are motor starters needed for pumps?
Complete protection and monitoring of pumps requires motor starter characteristics as follows:
- Lockable disconnect switch
- Hand – Off – Auto switch
- Motor starter / contactor
- Motor overload protection and monitoring contact
- Current sensor
- Design to start in Manual mode on line power – independent of control power.
Submersible pumps used in service stations typically have a control box that incorporates Items 3 and 4, with Item 1 covered by the circuit breaker within the building power distribution panel. These are typically not considered to be appropriate for emergency power fuel systems.
05.07 Why are duplex pumps used and how do they operate?
Duplex pumps are used to provide a secondary means of fuel transfer in the event of a failure of the primary pump. Each pump in a duplex set is sized to meet the full flow requirements of the system. 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.
05.08 Why are triplex pumps used and how do they operate?
Triplex pumps are often used where there is a wide variation in flow requirements, so that a single pump is activated initially, a second brought on-line at higher flow rate requirements and the third pump being a reserve backup. Triplex pumps are designed so that 2 pumps will serve the full flow requirements with a third pump as a backup to either of the operating pumps failing.
05.09 What is a line leak detector for a submersible pump?
Many State and local regulations require a line leak detector for pressurized underground piping. Line leak detectors for underground piping are used to detect a loss of integrity in the piping with a consequential shut down of the pump. There are 2 types of line leak detectors – mechanical and electrical.
Mechanical line leak detectors install on the submersible pump body. The pump must start against a closed valve to allow pressure to build in the line sufficiently to allow the line leak detector to open and flow. If pressure does not build in the line properly, then the mechanical line leak detector trips and restricts the pump flow.
Electronic line leak detectors operate in conjunction with a tank monitor such as a Veeder Root panel. After each pump run cycle, the panel turns on the pump automatically and measures the pressure in the line using a pressure transducer. The panel displays a pass / fail test result and may be required to be configured to disable th submersible pump.
Line leak detectors are designed to work reliably with motor fuel dispensing operations where dispensers include solenoid valves to work in conjunction with the submersible pumps. In emergency generator applications, especially mission critical applications, the devices can be problematic where test failures can shutdown the fuel supply system. Control systems need to include appropriate valve / pump timing controls to allow successful tests, and also detect failure and switch to a secondary pumps.