Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of
#2 diesel fuel but you must understand that #2 is a mix of various
fractions. From that standpoint alone and the potential of 'flashing
by vacuum application make vacuum a less conservative approach to fuel
delivery systems.

I don't think the typical Walbro fuel pump can pull such a vacuum.

Doug

"Rich Hampel" wrote in message
...
Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of
#2 diesel fuel but you must understand that #2 is a mix of various
fractions. From that standpoint alone and the potential of 'flashing
by vacuum application make vacuum a less conservative approach to fuel
delivery systems.

most single stage pumps will deliver approx 6" vacuum when
'deadheaded', at least thats what you design for as a maximum. .....
unless you have the manufacturers documents that include 'slip', etc.


In article , Doug Dotson
wrote:

I don't think the typical Walbro fuel pump can pull such a vacuum.

Doug

"Rich Hampel" wrote in message
...
Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of
#2 diesel fuel but you must understand that #2 is a mix of various
fractions. From that standpoint alone and the potential of 'flashing
by vacuum application make vacuum a less conservative approach to fuel
delivery systems.

most single stage pumps will deliver approx 6" vacuum when
'deadheaded', at least thats what you design for as a maximum. .....
unless you have the manufacturers documents that include 'slip', etc.


In article , Doug Dotson
wrote:

I don't think the typical Walbro fuel pump can pull such a vacuum.

Doug

"Rich Hampel" wrote in message
...
Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of
#2 diesel fuel but you must understand that #2 is a mix of various
fractions. From that standpoint alone and the potential of 'flashing
by vacuum application make vacuum a less conservative approach to fuel
delivery systems.

I don't think the typical Walbro fuel pump can pull such a vacuum.

Doug

"Rich Hampel" wrote in message
...
Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of
#2 diesel fuel but you must understand that #2 is a mix of various
fractions. From that standpoint alone and the potential of 'flashing
by vacuum application make vacuum a less conservative approach to fuel
delivery systems.

On Fri, 09 Jan 2004 14:47:50 GMT, Rich Hampel
wrote:

Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of

That's pretty much self regulating in this case. I.e., if you had a
pump that was strong enough to create a vapor lock due to a very high
vacuum, it would stop pumping and the vacuum would decrease and the
vapor lock would be cured.

But then again, if you had so much of a pressure difference on most of
the filters we're talking about here that the fuel boils due to the
vacuum of being drawn through the filter, it's time to change the
element anyway. Either that or the pump is too strong and will destroy
the filter.

Steve

On Fri, 09 Jan 2004 14:47:50 GMT, Rich Hampel
wrote:

Another good reason NOT to pull vacuum on fuels and other volitile
liquids is that if the vacuum exceeds the vapor pressure of the fluid
the liquid with boil (flash) or you will separate out the lighter
fractions (lighter weight hydrocarbons). If youve ever had a gasoline
that had 'vapor-lock' problems you'll understand this phenomenom. I
dont have by me at this time a listing of the vapor pressure range of

That's pretty much self regulating in this case. I.e., if you had a
pump that was strong enough to create a vapor lock due to a very high
vacuum, it would stop pumping and the vacuum would decrease and the
vapor lock would be cured.

But then again, if you had so much of a pressure difference on most of
the filters we're talking about here that the fuel boils due to the
vacuum of being drawn through the filter, it's time to change the
element anyway. Either that or the pump is too strong and will destroy
the filter.

Steve