Suctioning fuel from liquid condensate trap failing

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stuppid
Head Tech
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Joined: Thu Dec 23, 2010 7:10 am

Re: Suctioning fuel from liquid condensate trap failing

Post by stuppid » Thu Sep 10, 2020 2:43 pm

100 inches of water is 7.36 inches mercury.

From the bennet suction pump manual:

The Reason for Vapor Lock
Atmospheric Pressure of 14.7 PSI (Sea
Level) presses on the liquid in the tank.
See Figure 1.
Vapor Pressure (the amount of pressure
required to keep the product in a liquid
form at 60°F) of today’s product is
approximately 10 PSI.
See Figure 2
The difference between Atmospheric
Pressure and Vapor Pressure is known
as the Working Pressure. The Working
Pressure is all that the pump can create
without the product turning to vapor.
14.7 PSI Atmospheric Pressure
-10.0 PSI Vapor Pressure
4.7 PSI Working Pressure
Figure 1
Figure 2
Figure 3
24
The Cause of Vapor Lock (continued)
To measure a pump’s suction, the
Working Pressure must be converted to
inches of vacuum. To do this, multiply
the Working Pressure by 2. The result is
the number of inches of vacuum that a
pump can create before the product
changes to a vapor.
See Figure 4.
4.7 PSI Working Pressure = 9.4 inches
of vacuum.
See Figure 5.
Installation is the Key
The condition of installation dictates
how much suction a pump must create to
pump the product.
A. It takes 1 inch of vacuum to lift gas
1.5 feet vertically. To determine the
inches of vacuum required to lift the
gas in a system, follow this
procedure:
Measure the distance from the top of
the product in the tank to the center
of the pumping unit. See Figure 6.
Divide the distance by 1.5 to obtain
the inches of vacuum required by the
pump to lift the product.
Example: 9 feet of lift requires 6
inches of vacuum by the pump.
See Figure 6.
Figure 4
14.7 psi = 30” mercury (atmospheric
pressure at sea level). 14.7psi of
pressure will raise mercury in a tube to
30”
Figure 5
4.7psi = 9.4” of mercury
Figure 6
At 60o
F, 6 foot of lift requires prox 4” of
vacuum for example.
14.7 psi
equals
30” of mercury
25
The Cause of Vapor Lock
(Continued)
B. It takes 1 inch of vacuum by the
pump to overcome the restriction of
an angle check or foot valve. (Not
part of the pump, but a necessary
part of the installation.)
See Figure 7.
C. It takes 1 inch of vacuum by the
pump to overcome the restriction of
60 feet of horizontal piping from the
tank to the pump.
See Figure 8.
To obtain the inches of vacuum to
deliver product, simply add A, B and C.
A. 9 feet of lift = 6” of
suction
B. Angle check or
foot valve = 1” of suction
C. 60 feet
horizontal run = 1” of suction
TOTAL = 8” of suction
With 9.4” of suction to work with and
only 8” of vacuum required, conditions
are normal and the pump delivers
product without vapor locking.
Remember this condition exits when the
product is at 60°F.
Vapor Lock Conditions
Using the same example as above, 8” of
vacuum is still required to deliver
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.
1” of vacuum to overcome the restriction
of vertical check valve
Figure 7
60 feet of
horizontal piping
= 1” of vacuum.
60°F
Figure 8
N o r m a l
product
Figure 9
95°F
Vapor pressure of
product may be as
high as 12 PSI.
Figure 10
26
The Cause of Vapor Lock (continued)
Using the same formulas as above, the
Working Pressure equal Atmospheric
Pressure less the Vapor Pressure.
14.7 PSI Atmospheric Pressure
- 12.0 PSI Vapor Pressure of the
product
2.7 PSI Working Pressure
Multiplying the 2.7 Working Pressure by
2 equals 5.4 inches of vacuum that the
pump can create before the product turns
to vapor.
It still takes 8 inches of vacuum to
deliver product, but with higher
temperatures there is only 5.4 inches of
vacuum to lift the product. The result is
Vapor Lock.
As we have explained, the pump plays a
very small part in vapor lock situations.
Installation, the amount of product in the
storage tank and the Vapor Pressure of
the product are the main reasons for
vapor lock.
Example: Have you ever heard of vapor
lock in a diesel pump? No, because the
Vapor Pressure of diesel is
approximately 8 PSI.

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