Standby Power Solutions

Training and Consulting Safety Technical Articles Service Bulletins Transfer Switch Sequence of Operations	Service Bulletin: Oil Accumulation in LPG Liquid Withdrawal Fuel Systems March 4, 2003 This picture shows the typical Impco Vaporizer/Regulator used on LPG liquid withdrawal systems. The arrow points to the area where oil collects and blocks the flow of vaporized fuel to the carburetor. It has long been the practice of the manufacturers of Liquid Petroleum Gas to mix oil with the liquid fuel to lubricate their pumps, valves and other handling equipment. This practice normally presents no problem. However, when LPG is used as an engine fuel it can clog the LPG vapor side of the system and prevent fuel from reaching the carburetor. The oil is mixed with liquid fuel. The liquid is then vaporized in the engine mounted Impco Vaporizer/Regulator, but since the oil is heavier than the gas it does not vaporize. Rather, it collects in the low-pressure connections between the Vaporizer/Regulator and carburetor. The longer the engine runs, the more oil collects. Eventually the engine can no longer get fuel and failure occurs. The problem can be easily corrected by draining the vapor side fuel line. This may, however, be inconvenient. Some systems plug in less than fifty hours, and it may not be possible to keep a technician available to keep these lines clear. In all cases the vapor side fuel line should be drained at each semi-annual maintenance interval. I recommend you follow up with your maintenance companies and make sure they attended to this procedure. The following are a few issues that should be kept in mind when dealing with LPG liquid fuel systems: LPG suppliers do not like to place new fuel tanks on generator sites because unless an extended outage occurs the LPG supplier may not need to fill the tank often enough to justify the cost. As a result, old tanks are often used for generator fuel. A problem arises with this because oil tends to accumulate in old tanks. When a tank is used for home heating fuel, the gas is allowed to vaporize inside the tank. The charge of lubrication oil stays in the tank as the LPG gas is used up. The next time the tank is filled, a new charge of oil is added to the remnants of oil left over from the old load of fuel. After twenty years or so, a lot of oil remains in the tank. When an old tank like this is moved from a heating application to a generator application, the old leftover oil gets mixed with the new fuel allowing the excess oil to condense out and plug the fuel line. You should always make sure your LPG supplier uses a new fuel tank or at least cleans out an old tank before he installs it on your site. Onan sometimes uses a pipe thread compound that locks the threads. This makes it difficult if not impossible to safely disassemble the fuel systems in order to drain the oil. It is not uncommon to break the Vaporizer/Regulator when trying to drain the oil. Further, some of the Onan systems lack a drip leg to collect oil. These plug rapidly. Onan has long been aware of the problem. On the 30.0SK generators they sold in the late 70's, Onan installed the Vaporizer/Regular high on the engine so that the oil would not collect. It would drain down into the carburetor and harmlessly burn away. This was a selling point Onan used in marketing against Kohler who at that time allowed the oil to collect and plug the systems. *It is incredible that Onan forgot this basic aspect of physics in the interim between the manufacture of the 30.0SK and the 35.0EM.* LPG liquid systems generate pressures as high as 300 psi. All piping must be rated for this pressure. This means black pipe must be schedule 80 and copper must be specifically rated for 300 psi or greater. We have found soft copper and schedule 40 black pipe, clearly not rated for high pressure, used on LPG liquid systems. If LPG liquid piping is to be buried, it must be specifically designed for burial. Black pipe must be coated or taped and copper must be encased in conduit to prevent damage from stones or debris. You should check local codes. *We have found piping clearly marked "not for burial" buried in gravel. The photo on the left is a close-up of the photo on the right.* LPG liquid fuel lines must be supported and have a suitable flexible line installed between the fuel line and Vaporizer/Regulator. We have found copper fuel lines, on the liquid side, unsupported and acting as vibration isolators. This arrangement will fatigue the copper and cause it to break. Flexible fuel connections must be rated for high pressure. We have found standard low-pressure appliance type flexible connections, purchased from a hardware store, used as LPG liquid fuel lines. These will burst. PH4-4-03 Back to Service Bulletins Home

Training and Consulting
Safety
Technical Articles
Service Bulletins
Transfer Switch Sequence of Operations

Service Bulletin:

Oil Accumulation in
LPG Liquid Withdrawal
Fuel Systems
March 4, 2003

This picture shows the typical Impco Vaporizer/Regulator used on LPG liquid withdrawal systems.

The arrow points to the area where oil collects and blocks the flow of vaporized fuel to the carburetor.

It has long been the practice of the manufacturers of Liquid Petroleum Gas to mix oil with the liquid fuel to lubricate their pumps, valves and other handling equipment. This practice normally presents no problem. However, when LPG is used as an engine fuel it can clog the LPG vapor side of the system and prevent fuel from reaching the carburetor.

The oil is mixed with liquid fuel. The liquid is then vaporized in the engine mounted Impco Vaporizer/Regulator, but since the oil is heavier than the gas it does not vaporize. Rather, it collects in the low-pressure connections between the Vaporizer/Regulator and carburetor. The longer the engine runs, the more oil collects. Eventually the engine can no longer get fuel and failure occurs.

The problem can be easily corrected by draining the vapor side fuel line. This may, however, be inconvenient. Some systems plug in less than fifty hours, and it may not be possible to keep a technician available to keep these lines clear.

In all cases the vapor side fuel line should be drained at each semi-annual maintenance interval. I recommend you follow up with your maintenance companies and make sure they attended to this procedure.

The following are a few issues that should be kept in mind when dealing with LPG liquid fuel systems:

LPG suppliers do not like to place new fuel tanks on generator sites because unless an extended outage occurs the LPG supplier may not need to fill the tank often enough to justify the cost. As a result, old tanks are often used for generator fuel. A problem arises with this because oil tends to accumulate in old tanks.
When a tank is used for home heating fuel, the gas is allowed to vaporize inside the tank. The charge of lubrication oil stays in the tank as the LPG gas is used up. The next time the tank is filled, a new charge of oil is added to the remnants of oil left over from the old load of fuel. After twenty years or so, a lot of oil remains in the tank.
When an old tank like this is moved from a heating application to a generator application, the old leftover oil gets mixed with the new fuel allowing the excess oil to condense out and plug the fuel line.
You should always make sure your LPG supplier uses a new fuel tank or at least cleans out an old tank before he installs it on your site.
Onan sometimes uses a pipe thread compound that locks the threads. This makes it difficult if not impossible to safely disassemble the fuel systems in order to drain the oil. It is not uncommon to break the Vaporizer/Regulator when trying to drain the oil.
Further, some of the Onan systems lack a drip leg to collect oil. These plug rapidly.
Onan has long been aware of the problem. On the 30.0SK generators they sold in the late 70's, Onan installed the Vaporizer/Regular high on the engine so that the oil would not collect. It would drain down into the carburetor and harmlessly burn away. This was a selling point Onan used in marketing against Kohler who at that time allowed the oil to collect and plug the systems.
It is incredible that Onan forgot this basic aspect of physics in the interim between the manufacture of the 30.0SK and the 35.0EM.
LPG liquid systems generate pressures as high as 300 psi. All piping must be rated for this pressure. This means black pipe must be schedule 80 and copper must be specifically rated for 300 psi or greater.
We have found soft copper and schedule 40 black pipe, clearly not rated for high pressure, used on LPG liquid systems.
If LPG liquid piping is to be buried, it must be specifically designed for burial. Black pipe must be coated or taped and copper must be encased in conduit to prevent damage from stones or debris. You should check local codes.
We have found piping clearly marked "not for burial" buried in gravel. The photo on the left is a close-up of the photo on the right.
LPG liquid fuel lines must be supported and have a suitable flexible line installed between the fuel line and Vaporizer/Regulator.
We have found copper fuel lines, on the liquid side, unsupported and acting as vibration isolators. This arrangement will fatigue the copper and cause it to break.
Flexible fuel connections must be rated for high pressure.
We have found standard low-pressure appliance type flexible connections, purchased from a hardware store, used as LPG liquid fuel lines. These will burst.

PH4-4-03

Back to Service Bulletins
Home