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Oil Tank Pressure Levels & Pressure Tolerance
Residential Oil Tank Pressures During Testing & During Oil Tank Fill-up

  • OIL TANK PRESSURE - CONTENTS: How Much Pressure is There on a Home Heating Oil Tank During an Oil Delivery? What is the pumping rate in gpm and the pumping pressure in psi during a heating oil delivery ? What causes overpressure conditions in home heating oil tanks above ground or underground. How to avoid over-pressurizing a heating oil tank - Protection from Oil Tank Overfill - Methods. Role of oil tank delivery truck pump pressure setting, hose diameter & oil tank fill pipe size in oil tank pressures
  • POST a QUESTION or READ FAQs about the pressures encountered in and on oil storage tanks under various conditions
  • REFERENCES
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Oil storage tank pressure exposure & tolerance:

Here we explain the typical oil tank test pressure at the factory, the pressures that an oil tank is subjected to during oil tank fill-up, and the cause and prevention of excessive pressures that can cause leaks at oil tanks. We also answer the question of the amount of pressure to which an oil tank is subjected during an oil delivery, providing pressure limits, calculation of oil tank pressure changes, and listing both causes and steps to prevent over pressurizing a home heating oil tank.

This series of articles discusses the causes of leaks at oil tank fill or vent piping, what the leak and other hazards are, and what to do about oil tank piping leaks.



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Factory Test Pressures on Steel Heating Oil Tanks

Thanks to David Hollen, Applications & Technical Support, at pump manufacturer and distributor Yamada America for help with this data.

Oil tank pressure test label (C) Daniel Friedman Oil tank pressure test label (C) Daniel Friedman

Residential above ground steel heating oil tanks are typically factory tested to 5 psi to 7 psi by the manufacturer, as our two photographs of oil tank labels show (above).

Oil tank pressure test limits (C) Daniel FriedmanIn fact, as the labels show on oil tanks we photographed early in 2009 (at left and at the top of this page), some steel oil tank manufacturers specifically advise against further pressure testing of their oil tanks.

If you need to know the condition of an above-ground home heating oil tank after it has been installed, ask your heating oil company to perform a metal thickness scan of the oil tank. The technician will use a sonic test instrument to measure the thickness of the steel at a number of locations on the lower portion of the tank.

The reason the technician tests the lower tank areas is that it is there that corrosion and thus thinning of the tank steel most often occurs. This inspection procedure will not, however, detect a faulty tank weld nor piping errors in the heating oil handling system.

If you are concerned about the chances that a buried oil tank has leaked, you'll need to locate the tank and have appropriate soil tests performed. We discuss pressure testing of oil tanks
at OIL TANK LEAK TEST METHODS.

Effects and Amounts of Oil Tank Pressures During a Home Heating Oil Delivery

How Much Pressure is There on a Home Heating Oil Tank During an Oil Delivery?

Oil tank seepage (C) D FriedmanBut what is the pressure to which a heating oil tank is subjected during an oil delivery? The pressure experienced by the oil tank during fill from the home heating oil delivery truck is expected to be less than the oil tank manufacturer's tank test pressure (5-7 psi) if the oil tank is adequately vented.

A more detailed answer to the question of oil tank pressures is that it depends on several factors including the two main oil tank pressure factors listed below.

So What is the PSI Pressure the Oil Tank is Exposed To During Fill-Up?

Copper oil tank fill vent seepage (C) D FriedmanHome heating oil is delivered under pressure at many buildings: the oil delivery truck's hose nozzle latches onto a special fitting at the top of the oil tank fill-valve. When this type of connection is made, the driver can fill the oil tank more rapidly than otherwise, and also can avoid spillage around the oil tank fill pipe.

Just how much pressure an oil tank is subjected to during filling varies as follows:

Normal oil tank fill tank pressure: less than 5 psi on a properly vented heating oil tank (the presumed tank pressurization must be less than the manufacturer's factory tested tank pressure)

Totally-blocked or missing oil tank venting: pressures up to 280 psi - this would be an unusual condition such as an oil tank vent that has not only become totally blocked, but the vent blockage is not "blown out" by pressures created during the tank filling operation.

Anticipated partially-blocked oil tank venting: as oil tank pressure increases due to compressed air in the tank pressing against an obstruction in the oil tank vent pipe (such as an oil slug blocking the vent line or a cap blockage by an insect nest or a painted-over vent cap screen) the pressure may be sufficient to "blow out" a transient blockage of that type.

The pressure required depends on the solidity and adhesion of the blocking oil tank vent line debris. Our opinion is that considering the range of possible oil tank pressures, between 0 psi and over 200 psi (with a totally obstructed vent), it should be quite easy for an oil tank pressure to exceed the manufacturer's factory-test pressure of 5 to 7 psi.

Calculation of Increase in Oil Tank Pressure During Fill-up

If an oil tank is NOT vented, depending on how empty the tank was (how much air it contained), when the tank is filled it could be subjected to quite high pressure. Using BOYLE's LAW (P1V1 = P2V2),

then the pressure would increase from atmospheric (14.7 psi) to 294 psi. If we subtract out our starting 14.7 psi that means we've pressurized the tank to about 280 psi.

Examples of Causes of Excessive Pressures in a Heating Oil Tank

Restricted oil vent pipe (C) Daniel Friedman

Protection from Oil Tank Overfill - Methods

Because overfilling an oil tank might contribute to high oil tank pressures, we list some methods and products used to avoid over-filling a home heating oil tank:

Oil vent alarm whistle schematic - FD NYCReader Question: how is a vent alarm represented in plumbing drawings for oil tanks?

What is the drawing symbol for a vent whistle? - Anon. 11/7/11

Reply:

The schematic uses a simple representational shape at the oil tank vent pipe base connection to the oil tank and labels it as "vent alarm".

Anon, we took a look at the FDNY's training materials for the certification for supervising fuel oil piping & storage in buildings (above-left). Plumbing layout schematics for oil tank vent alarms or vent whistles may vary - we'll continue to look and post details here.

Four overfill protection devices used on USTs and in some cases ASTs include

Vent alarm, Vermont DECVent alarms are one of four common heating oil tank overfill protection device, but you should not rely on the alarm alone. Make sure that the fill and vent piping is properly sized, routed, and installed too.

  1. Overfill alarms - remote tank fill status indicators with an in-building audible alarm and light
  2. Automatic shutoff devices - a mechanical device built right into the fill piping on the oil tank. The automatic shutoff combines a float with a valve that closes in the intake pipe.
  3. Ball Float Valves - a similar overfill protection device mounted in a buried oil tank vent pipe
  4. Venty Alarms, vent whistles, tank whistles. Paraphrasing and editing from the State of Vermont DEC:

    A vent alarm, or vent whistle, is a small device, usually a tube, typically is installed between the oil storage tank and the vent pipe mounted at the tank top. The vent alarm provides an audible whistle as the oil tank is being filled: as oil is pumped into the tank, air is displaced from inside the tank through the vent alarm and the tank vent piping.

    When the level of the fuel reaches the end of the tube oil in the tank blocks air entry into the vent alarm, and the whistling stops. This indicates that the oil tank is full. Vent whistles are typically used on small tanks only. It is very uncommon to find a vent whistle on a tank larger than 2,000 gallons.[1]

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