There are 2 types of overfill prevention devices for above ground storage tanks
• Overfill Prevention Valve – Float rises with fuel and closes a valve at a set height.
• Tank Overfill Alarm – Also known as electronic alarms or alert devices. Provide an audible or visible warning via a Fuel Management System or Automatic Tank Gauge (ATG).
Overfill prevention devices must shutoff/activate at these levels set by the certified tank installation contractor at the time of installation:
• Overfill Prevention Valve – 95% of capacity
• Tank Overfill Alarm – 90% of capacity
At Fuelchief our DC Series of stationary tanks are fitted with both a mechanical Overfill Prevention Valve (OPV) and as an additional extra, can be fitted with a Tank Overfill Alarm.
• The Tank Overfill Alarm is set at 90% of tank capacity
• The OPV is set at 95% tank capacity as a secondary means of preventing the tank being overfilled.
At Fuelchief OPV’s are devices, that are used to protect from overfilling a tank (usually at 95% capacity). The valve uses a float that rises with the liquid level and closes a poppet within the drop tube. Effectively, these valves include mechanical devices that will shut off the flow of fuel oil when the tank reaches the present high level.
This video shows how the Ridart Overfill Prevention Valve (OPV) works in an above ground fuel tank.
Our OPV’s are from Ridart in Italy and are the leaders in this product. Their OPV is designed to be installed in an above ground storage tank and is designed to work correctly up to 8 bar of loading pressure.
To explain this better watch the video below from Ridart which highlights the different stages of filling and exactly what the OPV is to do.
The OPV is located within the drop tube and the drop tube is installed inside the fill pipe and the Tank Overfill Alarms can be a combination of sensors, visual/audible alarm, and ATG (Automatic Tank Gauge). The tank alarm sensor is typically installed in an access pipe located near the middle of the tank.
Above Ground Storage Tank (AST) owners should replace an improperly functioning tank overfill alarm when it is no longer working. How do you know if an overfill alarm is functioning properly? It would be impractical to fill an AST to 90% capacity just to test a tank alarm. Hiring a fuel system contractor that is certified in the maintenance of your equipment is the best way to test your system. The contractor will firstly check the battery of the alarm to make sure it is operational, remove the level sensor and verify it is set to the correct height that represents 90% capacity. Then they will raise the sensor and verify the audible and visual alarms are triggered.
Automatic shutoff devices must stop the flow of product before the tank reaches 95% capacity. A qualified tank contractor/technician will ensure the float arm on the OPV moves freely and the shutoff valve will close. It is important to verify that the shutoff device has not been tampered with or disabled.
It’s not uncommon for a float to be missing on older devices due to corrosion. As long as the float is attached, it is connected to the valve and seats properly in the drop tube then it meets the manufactures test recommendation.
Generally, there is one OPV in a tank, in the event it is a split compartment tank (storing both diesel and another fuel) then each fill point pay has its own OPV. So, in a split tank scenario, two OPV’s may be present. The technician will usually check one as part of their inspection. It is important to note that the secondary device does not interfere with the function of the primary. Overfull Alarms are set to close at 90% capacity and the OPV shutoff closes at 95% so they are not compatible. It is okay to use a fuel tank overfill alarm and shutoff valve in combination (which is what is used in Fuelchief tanks) as long as the alarm is set to operate at a lower level.
Below are some additional articles that may help in understanding the ins and outs of above ground fuel tanks better. Check out our case studies too to see what customers are saying.
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To find out more about how to maintain OPV’s contact your local service technician or contact Fuelchief via the link below.