Gasboy Gilbarco Global Pumping Unit Operation Manual - Manual (Page 40)

Vapor Lock Conditions Vapor Lock Causes
Page 36 MDE-4447A Global Pumping Unit Operation and Service Manual · May 2008
Vapor Lock Conditions
Using the same example as above, 8 inches of vacuum is still required to deliver the product.
With higher ambient temperatures, the vapor pressure of the product changes. As mentioned
above, the Vapor Pressure of today's product is 10 PSI at 60° F. At temperatures of 90° F or
higher, it can go as high as 12 PSI.
Figure 6-9: Vapor Pressure at 95º F
Using the same formulae in “Working Pressure” on page 32 , the Working Pressure equals
Atmospheric Pressure less the Vapor Pressure. See Figure 6-10 .
Figure 6-10: Working Pressure - Vapor Lock Conditions
14.7 PSI Atmospheric Pressure
- 12.0 PSI Vapor Pressure of the product
2.7 PSI Working Pressure
95º F
Vapor Pressure of Product
may be as high as 12 PSI
14.7 PSI
12.0 PSI
2.7 PSI
Atmospheric
Pressure
Less
Vapor Pressure
equals
Working Pressure
95º F