P.1 

OAR Box 1856 

Prepped by Keeia Richards 

Document Number: 

75) ll-A-12 

Docket Number: 

A-87-11 

Printed 11/24/2008 12:41:50 PM Sheet 75 of 82 
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f\-tf-\l IT-A-i 2. 

EPA-AA-SDSB-86-3 

-Technical Report 

Evaluation of the Feasibility 

of Liquid Fillneck Seals 

December 1986 

NOTICE 

Technical reports do not necessarily represent final EPA 

decisions or positions. They are intended to present technical 

analysis of issues using data which are currently available. 

The purpose in the release of such reports is to facilitate the 

exchange of technical information and to inform the public of 

technical developments which may form the basis for a final EPA 

decision, position or regulatory action. 

Standards Development and Support Branch 

Emission Control Technology Division 

Office of Mobile Sources 

Office of Air and Radiation 

U.S. Environmental Protection Agency 
P.3 

i 

Table of Contents 

Section Page 

I. Introduction/Overview 2 

II. Evaluation of Liquid Seal Concepts 5 

A. Preliminary Analysis and Experimental Design 5 

B. In-Tube Liquid Trap 13 

C. .J-Tube Liquid Seal 17 

D. Submerged Fill 20 

E. Techniques for Reducing Required Fill Height 23 

F. Discussion/Conclusions 28 

III. Bench Testing of a Liquid Seal Onboard System 35 

A. Description of the Prototype System 35 

B. Evaluation of System Efficiency 41 

IV. Conclusions 49 

References 53 

Appendix 54 
P.4 

-2-

I. Introduction/Overview 

The only significant uncontrolled source of hydrocarbon 

emissions from motor vehicles is the gasoline vapor which 

escapes during vehicle refueling. In an uncontrolled 

refueling, the vapors that are displaced during the refueling 

event pass through the fillneck and escape to the atmosphere. 

Systems designed to control these emissions are called 

refueling vapor control systems. When the controls are vehicle 

based, they are generally referred to as onboard vapor recovery 

systems. The essential ingredients of an onboard vapor 

recovery system are: 1) a fillneck seal to prevent vapors 

from escaping to the atmosphere via the fillneck, 2) a fuel 

tank vent and vapor line from the fuel tank to allow for 

displacement of refueling vapors, and 3) a method of removing 

hydrocarbons from the vapors displaced from the fuel tank and 

storing them for purging at a later time. Normally this is 

accomplished through the use of a carbon canister. 

This report is primarily concerned with fillneck seal 

portion of the onboard vapor recovery system. Historically, 

the fillneck seals most often discussed as part, of onboard 

systems are mechanical seals. In a mechanical seal system, a 

temporary physical barrier is created between the seal and the 

nozzle when the fuel nozzle is properly inserted into the 

fillneck (see Figure 1). This barrier (usually referred to as 

a seal) prevents the vapors from escaping out the fillneck when 

the fuel is dispensed. 

In an extensive development and testing program conducted 

in 1978, API demonstrated that mechanical seals can effectively 

prevent vapors from escaping through the fillneck over the 

useful life of a light-duty vehicle when used under normal 

conditions.[1] However, some concern has been expressed about 

the safety, durability, and integrity of the mechanical seal 

approach. 

Concerns about the mechanical seal fall in three areas: 

• Fillneck seals may require a pressure relief valve 

to deal with potential fuel tank overpressures which 

could occur as a result of failure of the fuel 

nozzle automatic shut-off mechanism or a blockage in 

the vapor line between the fuel tank and the carbon 

canister. Without a pressure relief valve, tank 

overpressures could result in a fuel spitback with 

potential fuel tank overpressures. 
Figure 1 

P.5 

FILL PIPE MODIFICATIONS 

ROTARY SEAL 

ROTARY SEALTRAP DOOR 

LEAD RESTRICTOR 

RLL PIPE MODIRCATIONS 

ROTARY SEAL 

ROTAPY SEAL 

TRAP DOOR 

SPOUT 

LEAD RESTRICTOR 
P.6 

-4-

• Under some adverse in-use conditions, a mechanical 

seal may require maintenance or replacement to 

retain a high in-use efficiency. This depends in 

large part on the material used to make the seal and 

the degree to which the mechanical seal mounting 

within the fillneck protects it from unusual wear or 

abuse. 

• If not properly designed, the mechanical seal may be 

susceptible to tampering by the consumer. 

Instead of using a mechanical seal in the fillneck, one 

alternative is the use of a liquid seal. The idea of using a 

liquid seal in the fillneck was introduced early in the 

development of onboard vapor recovery systems. A report 

published in 1973 by the American Petroleum Institute 

identified and briefly evaluated several different liquid seal 

concepts.[2] A liquid seal system uses a fillneck design which 

routes the incoming fuel in such a way that the fuel itself 

prevents the vapors from escaping via the fillneck. 

The use of a liquid seal design would help to eliminate 

the potential problems associated with a mechanical seal. 

Since a new seal is formed at each refueling, in use durability 

and maintenance are not in question. Also, since the liquid 

seal fillneck is no different in appearance than current 

fillnecks and the fuel itself forms the seal, liquid seals are 

essentially tamper-proof. The problem of overpressure during 

refueling would be eliminated, because fuel would back up in 

the fillneck as soon as any pressure built up. The fuel nozzle 

would then either shut off automatically or could be shut off 

manually, since the nozzle operator could see the overfill 

condition. In addition, liquid seal systems may be somewhat 

less costly than mechanical seals since a pressure relief 

device may not be required. 

The purpose of this report is to evaluate the liquid seal 

approach to fillneck vapor containment as a practical 

alternative to the more widely recognized mechanical seal. 

After evaluating several different liquid seal approaches, the 

performance of one of the liquid seal designs is then evaluated 

in a simple prototype onboard control system. 

The first portion of the report covers evaluation of the 

liquid seal concepts. It starts with a conceptual analysis of 

the liquid seal and provides an overview of the experimental 

and analytical methodology used in the testing. Then it 

examines each of three basic liquid seal designs individually: 

the "in-tube" liquid trap, the "J-tube," and the submerged 

fill. The testing done on each design is outlined and the 

strengths and weaknesses of each are noted. Next, a problem 
P.7 

-5-

comrnon to each design, air entrainment and bubble proliferation 

in the fillneck, is discussed and various methods of 

controlling these problems are evaluated. The first portion of 

the report closes with conclusions about the adaptability of 

these liquid seal designs to current fuel tank fillneck 

configurations. 

The second portion of the report discusses the performance 

of a crude, first generation liquid seal fillneck (J-tube) on a 

simple prototype onboard system. It begins with a description 

of the key components needed for an onboard control system and 

then describes the components used in EPA's system and how 

these met the performance criteria needed for the liquid seal. 

The test procedure used to evaluate the performance of this 

system in a series of bench tests is described and this is 

followed by a discussion of the test results including system 

efficiency and sources of emissions. 

The report then closes with some conclusions about the 

performance of liquid seals and compares them to results 

achieved for mechanical seals. 

II. Evaluation of Liquid Seal Concepts 

A. Preliminary Analysis and Experimental Design 

1. Introduction . 

The term "liquid seal" in the context of an onboard vapor 

recovery system refers to any system of fuel tank and fillneck 

in which a column of liquid separates in-tank vapor from 

atmospheric air. One key parameter in evaluating the 

feasibility and performance of liquid seals is the fill height 

required to maintain a liquid seal during a refueling event. 

If the fill height available is less than that needed, the fuel 

rising in the neck will cause a premature shut-off of the 

nozzle. One of the major goals in these evaluations was to 

determine the minimum fill heights necessary to completely 

refill the tank using liquid seals in the fillneck. This 

section develops some models which help to predict the manner 

in which these liquid seals would perform and what fill height 

might be necessary to make use of a liquid seal as an 

alternative to a mechanical seal. First, the static situation 

is discussed and a mathematical model relating fillneck height 

to tank backpressure in the static situation is presented. 

Then the dynamic effects that are part of a typical refueling 

event and that complicate the mathematical model are 

introduced. Third, an experimental design for testing the 

various fillneck configurations is outlined. Fourth, the 

general test procedure for testing the liquid seal concepts is 

developed. 
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• 6 -

2. Static Situation 

Any liquid trap system can be modeled by the simple 'U' 

tube system shown in Figure 2. In the static situation, the 

vertical fill height, hf, required to support any induced 

tank backpressure, PB, can be found using the basic equation 

of fluid statics. In this case: 

PB = Po + pghf, where 

PB = tank backpressure, gauge 

Po = reference gauge pressure at reference height, h = 0 

p = density of fluid in tank 

g = acceleration of gravity at test altitude 

hf = required fill height above reference height 

For example, to support a backpressure of 5 inches H20 

under static conditions, a gasoline column (specific gravity = 

0.72) would have to rise approximately 7 inches above the 

reference height. So vertical fill height would have to be at 

least 7 inches. During testing^ a water manometer was used to 

gauge pressure so that pressure could be read .directly in 

inches of H20. If fuels were dispensed very slowly, this 

model could be used to analyze the system. It is not, however, 

and the next section looks at the dynamic effects of a 

refueling. 

3. Dynamic Effects 

A number of factors complicate this model for a typical 

refueling event. These include: 

• Dynamics: At a typical gasoline pump fuel is 

dispensed at a rate of 7-10 gallons/minute 

(gal/min); thus the system is not static. 

• Injection effect: The kinetic energy of the 

gasoline as it flows out of the dispensing nozzle 

tends to aid the flow of gasoline into the tank and 

to reduce the required fill height. 

• Turbulence and air entrainment: The interaction 

between liquid and air in the fillneck is quite 

turbulent. This interaction tends to greatly 

increase the required fill height. 
Figure 2 - 'U' Tube 

Pb = tank backpressure, guage 

Po = o = reference guage pressure 

hf = required fillneck height 

P.9 
P.10 

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Observations during informal testing of the 'U' tube set 

up of Figure 2, support the intuitive hypothesis that required 

fill height is directly related to tank backpressure for any 

given fuel flow rate and fillneck configuration. In the static 

situation, PB and hr are related by a constant conversion 

factor, the liquid density. In the dynamic situation, the 

relationship is much more complex, with fluid density, 

viscosity, surface tension, and other factors all interacting 

in a highly turbulent flow. In this dynamic, turbulent 

situation, it was expected that PB and hr would vary 

directly and that an increase in tank backpressure would 

increase the fill height necessary to support that pressure. A 

mathematical analysis of such a turbulent, dynamic flow was 

outside the scope of this investigation, so a mathematical 

model was not developed. Instead, the relationship between 

tank backpressure and fillneck height was determined 

experimentally for the three liquid seals evaluated. 

4. Experimental Design 

The ultimate goal of the tests conducted by EPA was to 

compare the performance of a number of liquid seal fillneck 

configurations under uniform test conditions and procedures. 

Because the optimal experimental design was not intuitively 

obvious when testing began, a series of developmental tests 

were performed with water as the test fluid. These tests were 

done to evaluate a number of experimental designs without the 

safety concerns and expense involved with gasoline testing. 

These preliminary tests were performed using standard tap 

water, and fillneck systems were constructed using metal, 

tygon, and plexiglass. These systems were then attached to a 

standard automotive fuel tank having a nominal capacity of 

about 18 gallons. All gasoline tests were performed with 

indolene clear as the test fluid, and since plexiglass is 

incompatible with gasoline, systems were built of metal and 

tygon. The temperature during this testing was the prevailing 

ambient temperature (nominally 80°F). 

The developmental water tests were carried out in a 'U' 

tube system such as the one described above and diagrammed in 

Figure 2. Data was taken relating fill height to tank 

backpressure for different fillneck configurations during these 

developmental water tests. The numerical results of these 

tests proved to be of little use in predicting the results of 

the gasoline testing, however, because of the great differences 

in the properties of water and gasoline (see Table 1). 

However, the tests were very helpful in isolating the 

parameters that would prove critical in determining required 
P.11 

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Table 1 

i 

Properties of Water and Gasoline at 20°C 

Property Water Gasoline (n-Octane) 

Density (lb/gal) 8.30 5.83 

Viscosity (Centipoise) 1.0 0.54 

Surface Tension (Dynes/cm) 72.8 21.8 

Source: CRC - Chemistry and Physics Handbook and Perry's 

Chemical Engineering Handbook, 5th Ed. 
-10-

fillneck height. The qualitative results of this preliminary 

testing which are important to the experimental design are 

outlined below: 

• The system performed as predicted by the 'U' tube 

model - required fill height varied directly with 

tank backpressure. 

• Increasing fuel inflow rate increased required fill 

height. Bubbling caused by the mixing of fluid 

entering the fillneck with air in the fillneck was 

observed to increase as dispensing rate increased. 

• Changes in fillneck diameter (or volume per unit 

length) affected required fill heights. Generally, 

required fill heights increased with decreasing 

fillneck diameters. 

• The orientation of the dispensing nozzle in the 

fillneck affected fill height. If the nozzle was 

oriented appropriately, the liquid tended to adhere 

to the fillneck wall. If this was. done, air 

entrainment and bubbling were reduced leading to a 

decrease in required fill height. 

The results of these tests confirmed that these factors 

would have to be controlled to ensure consistent test results. 

Based on observations during the water testing, the U-tube 

system appeared to create a very adequate seal. To further 

evaluate the feasibility of this approach, a "u" was built into 

a 2-inch plexiglass pipe and tested using water. As will be 

discussed below, the testing showed that the smaller cross 

sectional area for flow within the trap required too high a 

fill height to be practical. However, this experiment revealed 

useful information on flow and turbulence characteristics. 

Based on the experience gained from this preliminary 

testing and supplemented by information contained in the SAE 

Recommended Practice regarding refueling emissions, standard 

test conditions were chosen to test the liquid seal fuel tank 

systems using gasoline under conditions likely to occur during 

a typical refueling event.[3] These conditions were used in 

the tests which evaluated the fill height requirements and 

other performance aspects of the liquid seals system. 

The backpressure was set at five inches H20. It is 

expected that carbon canisters and their accompanying tubing 

and valves can be designed to accommodate normal refueling 

rates with tank backpressures of 5 inches H20 or less. This 

is supported by experimental evidence presented in an API 
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report dated October, 1978.[1] The report quotes backpressures 

as low as 2 inches H20, at a refueling rate of eight 

gal/min. All three of the fillneck seal approaches evaluated 

by EPA were tested at 5 inches H20 backpressure and most were 

tested at some lesser backpressures. 

Fuel dispensing rate was also standardized. Typical fuel 

dispensing rates average from 7 to 10 gal/min, but the fuel 

cart available for use in this testing had a maximum fuel 

dispensing . rate of 7.5 gal/min. Therefore, this was the 

designated fuel flow rate for gasoline testing. 

As was mentioned above, fillneck cross sectional area also 

affects required fillneck height and had to be standardized. 

Because most stock fillnecks have an outer diameter of 

approximately two inches, this was chosen as the base fillneck 

diameter and tygon or metal tubing of this diameter was used. 

Also mentioned above, fuel nozzle orientation can also 

affect required fill height, but the optimal orientation is 

different for each fillneck configuration. Also, nozzle 

orientation is one of the key human factors . in vehicle 

refueling, and may vary significantly from operator to operator 

and vehicle to vehicle. For these reasons, fuel nozzle 

orientation was not standardized to minimize fill height. 

Instead, for each fillneck configuration the nozzle was 

oriented ih the manner that;, would normally occur in-use if the 

nozzle were to rest vertically in the fillneck perpendicular to 

the surface. 

The standard test conditions described above were then 

incorporated into the standard test procedure developed for the 

gasoline testing. The standard setup for testing the liquid 

seal designs is shown in Figure 3. The gate valve mounted on 

top of the tank was used to regulate the size of the orifice 

through which any vapor leaving the tank must pass. The 

backpressure induced in the fuel tank was controlled for any 

fuel inflow rate by changing the position of the gate valve. 

Prior to the start of each test, the manometer was zeroed, 

the fuel tank was leveled, and the gate valve opened to about 

one fourth of wide open. The fuel cart was turned on and fuel 

dispensed at the highest available rate. The gate valve was 

then closed until backpressure was stabilized at the desired 

value (initially, 5 inches H20) . The height of the 

fluid/bubble column in the fillneck was then measured when 

backpressure stabilized. This value was recorded as the 

required fill height. The tank was drained and the operation 

repeated. 
P.14 

Figure 3 

Standard Experimental Setup 

h = required fillneck height 

Box Represents 

Liquid Seal 

System 

/ 

Fill Nozzle 

T 

Gate Valve 

~l 

HL £. "1 

h 

0 

rt 

c 

T 
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At this point, fuel RVP and dispensed and tank temperature 

were not important. Neither the RVP of the fuel or the fuel 

temperatures mentioned above were controlled. 

The testing of each system generally adhered to the test 

procedure outlined above, although some details were specific 

to the individual systems being tested. The most significant 

difference between individual tests was the measurement of fill 

height. Fill height can be generally defined as follows: 

The value of the vertical component of a vector from a 

point on the plane of full tank fuel level to the point 

where the tip of the dispensing nozzle rests in the 

fillneck (the vertical distance from the tank full level 

to the nozzle tip). 

The peculiarities of the measurement of fill height for 

each individual system will be discussed in the sections of 

this report which deal with the specific designs. It should 

also be noted here that fill height, as used in this report, 

does not include the distance from the inserted nozzle tip to 

the gas cap location location.. This distance 

be included in any fillneck design. 

B. In-Tube Liquid Trap 

1. Introduction 

(2-3 inches) wpuld have to 

The first liquid seal approach tested was the "in-tube" 

liquid trap. The in-tube trap was chosen for study because the 

preliminary water testing showed that the system could provide 

a positive seal and could be installed by modifying only the 

fillneck, leaving the tank essentially unchanged. If this were 

possible, and the fillneck height requirements permitted, the 

design could be adapted to fit a number of vehicles. This 

section looks at the in-tube trap and its performance under the 

standard test conditions. 

An in-tube trap in the fillneck operates by creating a 

liquid barrier between the gasoline vapor in the tank and the 

atmosphere. Its operation is similar to that of the home sink 

drain pipe, but the 'U' shaped trap is built into the fillpipe 

rather than bending the fillpipe into a 'U' shape. 

A diagram of the in-tube liquid trap and illustrations of 

the parameters describing its construction are shown in Figure 

4. The trap was designed to divide the tube into three 

channels of equal cross-sectional area. Liquid is trapped in 

the upward opening 'U' , and if tank backpressure increases 
P.16 

Side View 

Figure 4 

In-Tube Trap 

3ottom 

View 

Dimensions 

Plexiglass 

a = c = 0.73" 

b = 0.54" 

D = 2.0" 

Metal 

a = c = 1.1" 

b = 0.8" 

D = 3.0" 

d = Trap Depth 

A = B = C 
P.17 

-15-

during refueling, a liquid column will rise above that 'U' 

until the pressure is offset. "Trap security" describes the 

susceptibility of the trap system to allowing vapor to pass 

through it during the refueling event. Trap security can be 

increased by increasing the depth of the liquid seal, but 

increasing this depth might also increase the required fillneck 

height. Normally, with an in-tube liquid trap, the depth would 

just need to be adequate to accommodate refueling on sloped 

terrain. So, to refuel on a 30° incline, a trap depth of 

one-half inch would be sufficient (for the large trap shown in 

Figure 4). 

Two traps were built for testing. The smaller trap was 

set in a two inch diameter plexiglass tube. This trap was 

built so that flow through the trap could be visually monitored 

during the preliminary water testing. A larger 3 inch diameter 

trap was built entirely of metal so that gasoline could be used 

as the primary test fluid. 

2. Test Procedures 

Figure 5 is a schematic of the experimental setup used to 

test the in-tube liquid traps. It is important to note the 

location of the trap in relation to the tank full level. If 

spatial efficiency were optimized in a production 

configuration, the trap would actually be at the roof of fuel 

tank inside the vapor space, and,, the upward opening 'U' would 

open at the tank full level. However, for the sake of 

convenience, these traps were built on top of the tank, and 

hence required fill height was measured from the top of the 

upward opening 'U' to the nozzle tip. 

3. Results/Discussion 

As was mentioned previously, some of the developmental 

testing discussed earlier in this report was done on an in-tube 

liquid trap. The dimensions of that trap are those listed 

under "Plexiglass" in Figure 4. The developmental testing 

showed that a trap built inside a 2 inch diameter tube would 

not be large enough to support a backpressure of 5 inches 

H20. The channels through which liquid was supposed to flow 

(approximately 1 square inch) simply were not large enough to 

allow liquid to pass through quickly. 

In order to accommodate gasoline and higher flow rates and 

to reduce required fillneck height, a larger in-tube trap was 

set in a 3 inch diameter tube. The dimensions of the trap are 

shown in Figure 4 under "Metal". Using the standard test 
Figure 5 

Experimental Setup For In-Tube Trap 

P.18 

Fill Nozzle 

Required 

Fillneck 

Height 

Full Tank 

Level 
P.19 

-17-

procedure, the tank was filled with a required fill height of 

only 11 inches. This is a very good result, considering that 

in the static "situation a neck height of 7 inches would be 

needed to support a 5 inch H20 backpressure (5 inches/0.72 = 

6.94 inches). The implications of this result are discussed 

later in the report. 

4. Conclusions 

A fill height of approximately 11 inches for the in-tube 

liquid trap is quite acceptable for many vehicle applications. 

However, the in-tube liquid trap approach has some drawbacks. 

First, the in-tube trap could be relatively complex to 

construct on a production basis. Also, since the trap required 

a 3 inch diameter fillneck to perform adequately under the 

standard test conditions, current fillpipe designs might have 

to be modified to accommodate its use.* A 3 inch diameter 

expansion in some fillnecks may create vehicle packaging 

problems. However no fuel tank changes would be necessary and 

the in-tube liquid trap has all the advantages of liquid seal 

systems that were described above. Packaging problems could be 

eliminated if the in-tube trap were built into the inside top 

of the fuel tank. The advantages and disadvantages of the 

in-tube trap are discussed further following the examination of 

the other liquid seal approaches. 

C. "J" Tube Liquid Seal 

1. Introduction 

The second liquid seal approach to refueling vapor 

containment examined was the 'J' tube liquid seal. The 'J' 

tube was chosen for study because it was a logical extension 

from the in-tube trap approach and would take only minor 

changes in fuel tank and fillneck to install and has all the 

advantages of liquid seals. This section looks at the fill 

height necessary for the 'J' tube system when evaluated under 

the standard test conditions. 

The 'J' tube system is shown in Figure 6. The 'J' tube is 

simply a modified 'U* tube (like t-hat shown in Figure 2). The 

difference is that in the 'J' system the fuel tank itself 

replaces the downstream, vertical portion of the drainpipe. 

The ultimate size of the trap and fillpipe diameter needed 

depend in part on the system backpressure. System 

backpressure less than the 5-inch H20 used here are 

achievable,* and would reduce the diameter of the in-tube 

trap. 
Figure 6 - *J' Tube 

^niLf 

«• HEIGH T 

nr,r~z:. — * T * ^

 F^«-<- «-F^ L 
P.21 

-19-

The dimensions of the 'J' system along with illustrations of 

some of the descriptive terms used in the discussion are given 

in Figure 6. It should be noted that the liquid trap is 

located inside the fuel tank, and the top of the trap is 

located on or near the full tank plane. This promotes spatial 

efficiency and makes maximum use of available fillneck height. 

2. Test Procedure 

Because the 'J'-tube trap is located inside of the fuel 

tank and fill height is measured from full tank level to the 

nozzle insertion point, the standard test method was followed 

exactly in this case. 

3. Results/Discussion 

The 'J' tube test results are listed below: 

Fuel dispensing rate = 7.5 gal/min. 

Backpressure 

(inches H-0) 

Required 

pUAc8§i?ht 

16.0 

13.5 

11.0 

5.0 

4.0 

3.0 

The 16 inches of fill height required to fill the tank at 

five inches H2O backpressure was more than expected based on 

extrapolation of the results of the developmental water tests 

discussed earlier. Although bubbling, due to the mixing of 

water with air in the fillneck, was observed during 

developmental tests, the violence of the bubbling during 

gasoline testing was not fully expected. The extensive 

bubbling in the fillneck was the cause of the large required 

fill heights. it was clear from this testing that if bubbling 

could be controlled, required fillneck heights could be 

reduced. This could be managed by reducing the backpressure or 

controlling the proliferation of bubbles in the fillneck during 

refueling. 

4. Conclusion 

The 'J' tube, a simple modification of the 'U' tube, was 

tested using the standard test method. Excessive turbulence 

and bubbling in the fillneck made a fill height of 16 inches 

necessary for refueling under the standard test conditions. 

The control of the bubble problem, and some methods of fillneck 

height reduction are discussed in section E. 

It is important to note that the *J' tube trap appeared to 

be doing its job of controlling emissions. A rough measurement 
-20-

of the hydrocarbon concentration at the fillneck mouth was 

taken with a lower explosive limit (LEL) meter. The meter 

showed no difference between the readings taken at the fillneck 

mouth and readings taken around the test chamber. 

D. Submerged Fill 

1. Introduction 

The third and final liquid seal system investigated was 

the submerged fill. In a submerged fill system, the fillneck 

opens into the fuel tank below the liquid surface. By filling 

the tank from below the surface, a liquid seal is naturally 

formed between in-tank vapor and atmospheric air. 

A drawing of a submerged fill system is shown in 

Figure 7. The significant features of the submerged fill 

system are listed below: 

• The security of the liquid trap is good and it 

improves as the tank fills. 

• A pressure relief valve would have to be 

incorporated into any submerged fill system. If the 

lines from fuel tank to carbon canister became 

blocked, tank pressurization during refueling could 

become a problem. If the backpressure in the tank 

rose between refuelings, when the gas cap was 

removed from the fillneck, the overpressure could 

cause gasoline to spit out of the neck. The 

pressure relief valve is needed to eliminate this 

problem. 

• The fillneck height is not critical during the early 

stages of refueling. Only in the last 10 percent of 

the fill is the full fill height used, as the back 

pressure caused by the fuel level in the tank 

increases. 

2. Test Procedure 

In a submerged fill system, the location of the top of the 

liquid trap rises as the tank fills. One major change was made 

in the standard test procedure to accommodate this unique 

feature of the submerged fill. Since the top of the liquid 

trap rises during refueling, the entire fillneck height is only 

needed during the final stage of refueling; when the top of the 

trap approaches the full tank liquid level. Therefore required 
P.23 

Figure 7 - Submerged Fil l 

rJOZZLi 

Fun . 
-22-

fill height must be measured just prior to the end of the 

refueling event. For these tests, fill height was measured 

when about 18 gallons of fuel had been dispensed (into a 

nominal 18 gallon tank). 

3. Results/Discussion 

The results of the testing of the submerged fill system, 

are presented below: 

Flow rate: 7.5 gal/min 

Backpressure 

(Inches H20) 

Required Fill 

Height (inches) 

5.0 

4.5 

16 

13 

These results are similar to the results for 

and the bubble problem was evident once again. 

the • 'J1 tube, 

There has been some previous 

effectiveness of the submerged 

refueling vapors. Preliminary lab 

found the submerged fill to be an 

work done to 

fill seal in 

work done by 

effective method 

evaluate the 

controlling 

EPA in 1979 

of refueling 

vapor control.[4] Crude sampling done with an LEL meter 

supports this finding. Samples taken during refueling from 

near the mouth of the fillneck showed no higher hydrocarbon 

concentrations than did background samples. 

4. Conclusions 

The submerged fill approach was evaluated using the 

standard test procedure, and required fill height was measured 

just prior to completion of the refueling. At a backpressure 

of 5 inches H2O a fill height of about 16 inches was needed 

to accommodate the large liquid/bubble column in the fillneck 

caused by excessive turbulence and air entrainment during 

refueling. 

There are fuel tank fillneck configurations currently in 

use that could not be easily adapted to accommodate fillneck 

heights of 16 inches. Since bubbling in the fillneck is the 

reason for the larger fill heights, a reduction in the bubbling 

should lead to a lower required fill height. The next section 

of the report addresses the bubbling problem and possible 

control techniques. 
-23-

E. Techniques For Reducing Required Fill Height 

1. Introduction 

All the liquid seal systems built with 2 inch diameter 

tubing needed extended fillnecks to accommodate the large 

gasoline/bubble column that rose above the liquid/air interface 

in the fillneck during refueling. This section of the report 

examines bubbling and air entrainment during refueling and 

evaluates some possible methods of fill height reduction. 

Bubbling is caused by: 1) the violent mixing of the gasoline 

leaving the dispensing nozzle with that already in the 

fillneck, and 2) air entrained in the fluid flow by the venturi 

system in the dispensing nozzle. 

There are three basic means of controlling bubbling in the 

fillneck through modification of the fillneck. The first is to 

reduce the violence of the mixing of dispensed fuel with that 

already in the fillneck. Another is to physically obstruct or 

direct the backup of bubbles in the neck. The third is to 

create a system to dissipate the kinetic energy of the 

dispensed fuel. 

Also, part' of the bubble problem could be eliminated by 

reducing the amount of air being entrained in the fuel during 

refueling. This air entrainment is caused by two phenomena. 

First, the automatic shutoff . venturi system in standard fuel 

dispensing equipment adds air to the fuel being dispensed. 

Second, air is entrained in the fuel as a by-product of the 

turbulence in the fillneck. The second of these two phenomena 

can be affected by fillneck modifications while the first could 

only be changed by modifying the nozzle. This section looks at 

the problems of air entrainment and bubbling, and examines some 

fillneck modifications designed to control bubbling and reduce 

fill heights. 

2. Air Entrainment 

The entrainment of air in the fluid flow affects fill 

height in.two ways. First, as fuel is dispensed and mixes with 

fuel in the fillneck, air is drawn into the mixture and bubbles 

are formed increasing required fill height. Second, if air 

makes its .way into the fuel tank with the fuel, the amount of 

vapor forced out of the tank during refueling and the tank 

backpressure (for a given flow rate) are increased. The 

bubbling problem is discussed in the next section of the 

report. This section looks at the entrained air that makes its 

way into the fuel tank. 
-24-

A test was performed on the 'J' tube system to determine 

if air was entering the tank along with gasoline. The tank was 

filled with 20 gallons of gasoline and the vapors displaced by 

the gasoline were collected and the volume of those vapors 

measured by pulling the vapors through a dry gas meter.* Both 

the dispensed and tank fuel were at the prevailing temperature, 

so vapor expansion or shrinkage should have been near zero. 

The results of the tests are shown below: 

Gasoline Dispensed Vapor Collected 

Trial No. (gallons) (gallons) 

1 20 22.2 

2 20 22.4 

3 20 22.8 

No attempts were made to identify the sources of the 

entrained air, but it was fairly evident that it was caused by 

air bubbles being trapped in the fuel entering the tank. This 

in turn was caused by the turbulent mixing in the fillneck. 

Although this testing was conducted on the J-tube system, it is 

also likely to occur to similar degrees in both the submerged 

fill and in-tube trap. 

The phenomenon of entrained air entering the fuel tank is 

significant. When the carbon canister and tubing are designed 

for a given liquid seal configuration, the amount of air 

entrained must be determined and figured in the design. 

Systems that allow more air to enter the fuel tank will need to 

transport more vapor at a given fuel inflow rate. This may 

also increase the hydrocarbon load to be captured by the 

canister, since the entrained air may enhance evaporation of 

the dispensed fuel. Some of the entrainment may be avoided 

through the control of the mixing of gasoline and air in the 

fillneck. This is examined next. 

3. Bubbling and Turbulence 

The most obvious source of bubbling in the fillneck is the 

violent mixing of the gasoline being dispensed with the 

gasoline already in the fillneck. To examine bubble formation, 

a tygon fillneck was mounted on the 'J' tube system, and the 

pattern of bubble flow in the neck was observed. Although the 

pattern of flow depends on the orientation of the fuel 

It was possible to put 20 gallons of liquid in a tank 

having a nominal capacity of 18 gallons because the tank 

was modified with a liquid seal and vent, but did not have 

a fill limiter. Thus the vapor space of the tank also 

contained fuel, which would not normally be the case. 
-25-

dispensing nozzle in the fillneck and on the configuration and 

cross-sectional shape and area of the fillneck, a typical 

bubble pattern is shown in Figure 8. The pattern shown was 

generated in a two inch diameter tube with a round 

cross-section. The sketch is helpful in that it highlights the 

point of bubble generation and shows the route that the bubbles 

take in climbing toward the automatic shutoff port on the 

nozzle. Since gasoline bubbles in the fillneck could 

contribute to premature nozzle shut-offs, several different 

techniques to reduce bubble generation were examined. These 

included approaches to eliminating bubbles before they reached 

the fuel nozzle and approaches to reducing bubble formation by 

decreasing the amount of turbulent mixing in the fillneck. 

While the approaches examined here were by no means 

comprehensive, (i.e., many other options exist) one approach 

identified was quite successful. 

This approach involved replacing a section of the standard 

2 inch diameter tubing with a section of 4 inch, diameter 

tubing. The resulting 'reservoir' added volume to the fillneck 

and served as a settling chamber in which the bubbles formed 

and burst without rising in the fillneck. The use of such a 

reservoir, the dimensions of which were chosen rather 

arbitrarily, had a significant, impact on required fillneck 

height. 

The reservoir idea was tested as an addition to the J-tube 

setup discussed in Section c. The reservoir is diagrammed in 

Figure 9. The procedure used to gauge required fillneck height 

was the same as that used for the J-tube without the 

reservoir. The results of testing this system are shown below: 

Fuel inflow rate = 7.5 gal/min 

Backpressure Required Fillneck 

(inches H2O) Height (inches) 

5 11 

4 9.5 

3 6.5 

Similar results were obtained when the in-tube trap and 

submerged fill systems were tested with reservoir type 

fillnecks. The in-tube trap set in 3 inch diameter tubing has 

a "built in" reservoir - the tubing is larger than the stock, 

system already. This seal system needed a fill height of only 

11 inches. The submerged fill system, with the reservoir used 

for the 'J' tube attached, achieved similar results (11 inches 

required fill height). The results of this test show that a 

f

roperly designed reservoir system can greatly reduce required 

illneck height. 
P.28 

Figure 8 

Bubble Flow 

Pattern 

Static Case 

Liquid Level 
P.29 

Figure 9 

Resevoir 

Top View 

Side View 

To Nozzle 

< — 2. lo.- * 

4 in. 

Stock Fillneck 

Reservior 

To Tank 
P.30 

-28-

Another approach to bubble control involves the use of a 

simple baffle to control flow in the fillneck as is now used in 

some vehicle designs. More specifically the inflow of fuel and 

the backflow of bubbles can be separated with the use of a 

baffling system. The simple baffling system shown in Figure 10 

directs and smooths the inflow of fuel and also directs and 

restrains the backflow of bubbles. The baffle restricts inflow 

to one portion of the fillneck and encourages much of the 

bubble backflow to rise in the other. The vents near the top 

of the baffle allow circulating air and vapor to pass through 

the baffle, but any remaining bubbles are popped by the edges 

of the vents before they can reach the nozzle venturi tube. 

Tests were conducted to determine the fillneck height 

requirement for the submerged fill tank with a baffled 

fillneck. The procedure described in Section D.3. for the 

submerged fill without baffling was followed. At a fuel inflow 

rate of 7.5 gal/min and tank backpressure of 5 inches H20, 

required fillneck height was reduced to 11.5 inches, a decrease 

of 5.5 inches. 

The baffle approach was not evaluated with .the in-tube 

trap or J-tube, but could be used if the baffle extended for 

enough into the liquid to separate the liquid/bubble flow. 

4. Discussion 

The reservoir and baffle approaches discussed above were 

successful in reducing fillneck height requirements by about 30 

percent. Of the portion of the fillneck height that can be 

attributed to the dynamic affects of refueling, the reduction 

is approximately 55 percent. This reduction is quite 

significant given the limited time and resources committed to 

this effort, and suggests further improvement is possible. 

F. Discussion/Conclusions 

1. Summary 

One of the key components of an onboard refueling vapor 

recovery system is a fillneck seal to prevent the escape of 

vapors during refueling. While mechanical seal approaches have 

been demonstrated successfully, there are concerns about the 

safety, durability, and integrity of the mechanical seal 

approach.' As an alternative to a mechanical seal, EPA has 

evaluated the practicality of implementing a liquid seal 

approach. 

The practicality aspect of the liquid seal approach 

involves three factors: fill height requirements, safety, and 

system efficiency. System efficiency is discussed in the next 
P.31 

Figure 10 

Baffled Fillneck 

Nozzle 

Inflow 

____ _ _JU 

Side View Front View 
-30-

portion of this report. Fill height requirements are important 

because of concerns regarding premature nozzle shut-off. In 

order to evaluate the potential suitability of various liquid 

seals with respect to fill height requirements, systems were 

tested under standard test conditions: a fuel dispensing rate 

of 7.5 gal/min and a tank backpressure of 5 inches H20. The 

vertical fillneck height required for normal refueling on each 

at the three liquid seal approaches was measured and recorded 

for each system. 

Due to the excessive amount of bubbling generated during 

refueling, fillneck heights of at least 16 inches were needed 

to refuel the tank for the J-tube and submerged fill 

approaches. Because of fillneck height limitations imposed by 

some current vehicle models, efforts were made to reduce the 

fill height requirements of the liquid seal systems. This 

involved fillneck modifications aimed at controlling air 

entrainment and bubbling in the fillneck. Through the use of 

reservoirs and baffles, fill heights were reduced to 11 

inches. The reduction of 5 inches is significant, considering 

that seven inches of fillneck height would be necessary to 

support a backpressure of 5 inches H20 under static 

conditions. The effect of dynamics was reduced to 4 inches. 

The results of the fill height evaluations are summarized in 

Table 2. 

The safety of liquid . seal approaches must also be 

considered. Most notably, liquid seal systems cannot 

pressurize during refueling such as could occur for mechanical 

seal systems. Any increase in pressure during refueling would 

cause fuel to rise in the fillneck and automatic shutoff to 

occur. The one safety problem that must be addressed for the 

liquid seal system is the possible spitback of fuel when the 

gas cap is removed prior to refueling. 

Spit back could occur if the lines to the carbon canister 

became blocked and pressure built in the tank prior to 

refueling. When the gas cap was removed, some of the fuel 

forming the liquid seal could be forced out of the fillneck as 

pressure equalized. Spit back can be avoided by either 1) 

removing the liquid seal after refueling or 2) including a 

pressure relief system to vent tank pressure before spit back 

can occur. The in-tube trap and 'J' tube use the first 

alternative. By drilling a small hole at the bottom of the 

upward opening 'U' in these designs, the liquid trap can 

operate during refueling, and then drain soon after the event 

has been completed. 
-31-

Table 2 

Bench Test Fill Height Requirement 

System 

In-Tube Trap 

J-Tube 

Submerged Fill 

Static 

7" 

7" 

7" 

Base 

System 

-

16" 

16" 

11" 

11" 

11" 

Modified 

System 

(3" pipe 

(reservo 

(baffle) 

5" H20 backpressure, 7.5 gpm dispensing rate, 2" fillpipe 

diameter. 
-32-

The submerged fill system, on the other hand, must include 

a more complex pressure relief system. There are a number of 

ways to incorporate the pressure relief system into the 

submerged fill. One of the simpler pressure relief systems is 

shown in Figure 11. The small tube enters the tank above the 

full tank liquid level, so it is never submerged. As refueling 

takes place, the *U' portion of the small tube is filled with 

fluid. When the gas cap is removed prior to refueling, the 

pressure is vented through the small tube before spitback can 

occur. The. amount of pressure needed to vent the system can be 

changed by changing the depth of the 'U' portion of the small 

tube. Although the spit back problem can be easily solved for 

any of the systems, the alteration of the submerged fill is 

clearly more complex than that required for the in-tube trap or 

'J' tube liquid seals. 

2. Conclusions 

There are two main questions to be addressed in concluding 

the first portion of this report. First, is the liquid seal 

approach to fillneck vapor containment a practical alternative 

to the mechanical seal as part of an onboard refueling vapor 

recovery system? Second, which systems tested in the study are 

the most promising for further development? 

The answer to the first of these questions is generally 

yes. The liquid seal could, be adapted to fit most light-duty 

vehicles and trucks as currently produced, but there are some 

vehicles that do not provide adequate fill height to employ the 

liquid seal. There are two major classes of fillneck 

configurations, the side fill and the rear fill. The side fill 

configurations will be discussed first. 

The liquid seal design is adaptable to most side fill 

vehicles. In fact, most vehicles could probably be equipped 

with an unmodified fillneck (no baffle or reservoir) . For 

other vehicle models, the length of the fillneck is sufficient 

to permit the use of a liquid seal with a modified, bubble 

reducing fillneck. Further, it appears that changes could be 

made in most side fill vehicles to increase the fillneck height 

if needed, by changing the location of the gas cap on the 

vehicle body. 

Rear fill configurations are much less receptive to the 

liquid seal approach than are side fills. The fillneck height 

of some rear fill vehicles is as little as 5 inches. A fill 

height of 5 inches could accommodate a backpressure of only 

3.15 inches H20 under static conditions. The limited testing 

conducted by EPA suggests that with a carefully designed 
P.35 

Figure 11 

Submerged Fill with Pressure Relief 

^ank Overpressure 

Relief Valve 
P.36 

-34-

reservoir, a fillneck height could probably be reduced to 

approximately 6.0 inches (3.0 inch H20 backpressure and a 7.5 

gal/min fill rate). If a manufacturer were convinced of the 

superiority of the rear fill configuration, and wanted to use a 

liquid seal system, changes in fuel tank and gas cap locations 

would have to be made. However, these changes might be 

relatively involved. Another approach would be to create a 

horizontal reservoir by extending the fillpipe horizontally 

across the top of the fuel tank, (either outside or inside) . 

The fuel would then enter the tank at the opposite end. 

Another option open to manufacturers of rear fill vehicles 

would be the use of a mechanical seal. The accompanying safety 

concerns would have to be addressed. Nevertheless, it is 

important to note that most current rear fill vehicle models 

are being phased out and no new models of this design have been 

introduced recently. In the post 1990 time frame few, if any, 

new models with rear fill tanks are expected in the new 

car/light truck fleet. 

The second question to be addressed is which system 

examined is promising for further development. There are four 

characteristics that are important in comparing these liquid 

seals. The first is the spatial efficiency of the system as 

measured by required fill height. The test results suggest 

that all of the systems can be modified to get nearly equal 

results. Each system evaluated needed a fillneck height of 

approximately 11 inches to .support a backpressure of 5 inches 

H20 at a fuel dispensing rate of 7.5 gal/min. The submerged 

fill system does have an advantage in this area, however, since 

the full fill height is needed only as the tank approaches the 

full level. 

Refueling safety is the second major characteristic for 

comparison of the liquid seal systems. Both the in-tube trap 

and 'J' tube need only one minor modification to avoid any 

spitback problem. However, the submerged fill system needs a 

pressure relief system like that described earlier. The 

submerged fill system is at a disadvantage in this respect. 

The third characteristic of comparison for these systems 

is the complexity of the liquid seal itself. The in-tube trap 

is the most complex of the three. The submerged fill and 'J' 

tube designs would be much less difficult to build and are 

probably more practical for this reason. 

The final basis of comparison is the security of the 

liquid seal defined in terms of the probability of vapor 

escaping to the atmosphere during refueling. The biggest 

concern about t.ap security arises when a vehicle sits on 

sloped terrain during refueling. The in-tube trap and 'J' tube 
P.37 

-35-

traps can be designed to ensure security up to any reasonable 

angle chosen. The submerged fill system works differently than 

these systems, however. For the submerged fill to function 

properly, the fuel must enter the tank below the liquid 

surface, but when the tank is nearly empty, the mouth of the 

fillneck will be only slightly below the liquid level. If the 

vehicle were on an incline, the fillneck may not be submerged 

at all or may be only partially submerged, and some vapor could 

escape during the early stages of refueling. 

It is clear from the discussion that each system has both 

strong and weak points, but most of the problems with any of 

the systems can be resolved with a. moderate amount of effort. 

The relative complexity of the in-tube trap suggests that this 

design may be the most costly to produce, but if installed in 

the inside top of the tank it could be implemented with no 

other fillpipe modifications. The other two systems are also 

clearly worth further investigation if the liquid seal concept 

is being developed. Based on the safety advantage, the J-tube 

is somewhat preferable to the submerged fill, and EPA has 

selected that approach for inclusion in the prototype liquid 

seal onboard system developed for bench testing. . The J-tube 

was also selected because of EPA's previous experience with the 

submerged fill which showed very high efficiencies in a bench 

test.[4] 

The next portion of this report covers EPA's program to 

evaluate the efficiency of a J-tube liquid seal. The 

discussions cover the remainder of the components needed for a 

bench evaluation of the system and the efficiency testing 

conducted by EPA. 

Ill. Bench Testing of a Liquid Seal Onboard System 

A. Description of the Prototype System 

1. Introduction 

Once the evaluation of the three liquid seal concepts was 

complete, EPA desired to evaluate the efficiency of a liquid 

seal in a simple prototype onboard refueling control system. 

As will be described below, the prototype system constructed 

for this evaluation was relatively crude, and incorporated only 

the essential components. No attempts were made to add 

components or incorporate modifications to reduce the refueling 

emission rate or optimize system efficiency. This section of 

the report briefly examines the three components added 

downstream of the fuel tank to complete the prototype system. 
P.38 

-36-

To complete the prototype system three additional 

components were needed. These include a fill limiter, a 

properly sized' vapor line, and an activated carbon canister. 

Each of these components is discussed below, in the context of 

the flow rate and backpressure design characteristics mentioned 

above and the overall efficiency of the prototype system. 

2. Fill Limiter 

While.it does not directly affect system backpressure or 

efficiency, a fill limiter is needed in onboard system designs 

where the vapor vent outlet is located in the fuel tank vapor 

drive. On present fuel tanks, the automatic shut-off feature 

of the fuel nozzle is activated when tank back pressure 

increases at the end of the refueling event and causes the fuel 

in the tank to back up into the fillneck and cover the nozzle 

spout with liquid. However, with a properly designed onboard 

system fuel tank backpressures are minimal since vapor is 

vented during refueling. The small amount of system 

backpressure which does exist is not adequate to back the fuel 

up into the fillneck and allow operation of the automatic 

shut-off feature of the fuel nozzle. Therefore, a .fill limiter 

is needed to close the vapor vent when the tank is full and 

thus increase the backpressure. Without a fill limiter it is 

quite possible that the tank could be filled well beyond its 

nominal capacity. For onboard equipped vehicles using side 

fill tanks with external .vent lines (as in Figure 12), the 

onboard system has little effect on the refueling process. The 

refueling event terminates the way it does on present vehicles, 

and thus a fill limiter is not needed. 

The EPA prototype onboard system used a rear fill fuel 

tank without an external vent line, so a simple float valve was 

needed as a fill limiter. The float was constructed of the 

same material used for the tank's fuel level indicator. It was 

suspended from the roof of the tank on a simple wire in such a 

way that it would float on the fuel as the tank approached 

full, and would nest into the vapor vent when the tank was 

full. This would stop the venting of vapor which would 

immediately increase system backpressure and thus would quickly 

lead to activation of the nozzle automatic shut-off. 

Before discussing the vapor line, two points about the 

fill limiter and its operation should be noted. First, EPA's 

simple prototype did not include a liquid/vapor separator, 

rollover valve or a vent closure valve. These were not 

necessary for a simple bench set-up intended only for 

evaluation of refueling emissions control. Second, EPA did not 

experience significant problems with fuel spillage due to 

operation of the fill limiter, as has been suggested by 
Figure 12 

Typical Current Evaporative System 

PRESSURE/VACUUM 

RELIEF CAP 

EXTERNAL VENT LINE 

FLOAT/ROLLOVER 

VALVE 

• 

3/8" DIA. 

8' LONG 

^ 

.05" DIA. LIMITING 

ORIFICE 

14 GALLON FUEL TANK 

PURGE VALVE 

1 LITER 

CARBON 

CANISTER 

TO PURGE 

INDUCTION 

POINT 
P.40 

-38-

some.[5] This perhaps was due to the fact that the system 

evaluated by EPA included a reservoir in the fillneck. 

3. Vapor Line 

The purpose of the vapor line is to convey gasoline vapor 

from the fuel tank to the carbon canister. It must be sized 

and constructed of material such that it does not unnecessarily 

increase the system backpressure (which affects the fill height 

requirement), and must be impermeable to gasoline vapors. To 

meet these requirements, three characteristics of the vapor 

line and its use must be considered and evaluated 

concurrently. These include the vapor line diameter, the vapor 

line configuration or layout, and the vapor line material. The 

affect of these three characteristics on system backpressure 

and permeability of vapors is discussed below. 

As gasoline vapors flow through the lines, both major and 

minor pressure losses occur which inhibit vapor flow and 

directly affect system backpressure. The vapor line diameter 

makes a major contribution to the pressure losses, since it 

represents a major contraction in the flow. The . other major 

pressure losses are caused by functional resistance to the 

vapor flow. This is a function of the vapor line diameter, 

length of vapor line used, and to some degree the vapor line 

material. 

Minor pressure losses are mainly caused by the vapor line 

layout or configuration. This includes any bends, elbows, 

expansions or contractions in the line, as well as any other 

deviations from the straight flow in a vapor line of a constant 

cross sectional area. 

As was discussed earlier in relation to fillneck seals, 

the control system was designed so that the vapor line and 

canister result in a fuel tank backpressure of no more than 5 

inches of H20. A series of tests was designed to empirically 

determine what size vapor line would be appropriate for a 

typical light duty vehicle application. These tests were 

performed on complete control systems (J-tube equipped fuel 

tank, vapor line, carbon canister) subjected to actual 

refuelings. The test conditions were constant except for the 

cross-sectional area of the tubing which was varied from test 

to test. Although only one tubing material was tested, the 

tests (summarized in Table 3) showed that vapor line with an 

inner diameter of at least 1/2 inch would have to be used to 

keep back pressure below 5 inches H20 for the entire system. 

To be safe, vapor line of 5/8 inch inner diameter was used for 
P.41 

-39-

Table 3 

Vapor Line Pressure Drop Contributions 

P, Inches H20 

Tube ID, Inch 

3/8 

1/2 

5/8 

1/2 

5/8 

Tube 

15 

15 

15 

8 

12 

Conf: 

ft., 

ft., 

ft., 

ft., 

ft., 

iguration 

6 bends 

6 

6 

4 

4 

bends 

bends 

bends 

bends 

Bench Test 

5 

2.2 

1.2 

1.5 

.9 
P.42 

-40-

control system testing, although 1/2 inch vapor would clearly 

be reasonable for many vehicle applications.* 

The tubing material is also very important to the 

functioning of the control system. The most important 

characteristic of appropriate tubing materials is 

impermeability to gasoline and gasoline vapors. If a vapor 

line which was permeable to gasoline vapors was used as part of 

the control system, hydrocarbons could escape from the tubing, 

defeating the purpose of the control system. There are a 

number of tubing materials which would be appropriate for this 

application. Flexibility, density and cost characteristics are 

all factors to be weighed in deciding between hard rubber, 

softer, more flexible rubber and steel materials. A double 

walled, flexible rubber fuel line was used in EPA'a prototype 

onboard control system since 5/8 inch impermeable vapor line 

was not commercially available. 

4. Carbon Canister 

Activated carbon for capture and storage of gasoline 

vapors has been used successfully in automotive applications 

for more than ten years. To apply this technology to control 

of refueling emissions in EPA's bench evaluation, the canister 

must not increase system backpressure more than is necessary, 

and it must be sized and loaded with enough activated carbon to 

efficiently capture essentially all refueling emissions. These 

two factors are closely linked since canister size and design 

both impact backpressure. 

Rather than designing an optimum canister, it was EPA's 

goal to construct or obtain a canister which was adequately 

sized to capture all refueling emissions from an 18 gallon fuel 

tank and yet would not increase total system backpressure to 

more than 5 inches H20. 

First, to assist in meeting the backpressure reguirement, 

EPA held discussions with several manufacturers of activated 

carbon. Based on these discussions, EPA selected Westvaco 

extruded wood base activated carbon for use in the canister. 

Information presented by the vendor indicated that the extruded 

activated carbon might have a higher working butane working 

capacity and better pressure drop characteristics than the more 

conventional activated carbons now used in evaporative emission 

applications. However, it appears that any of the activated 

carbon types sold by the different companies would also work 

successfully in capturing refueling vapors, but these would 

This discussion briefly addresses how vapor line diameter 

affects backpressure. Any system design would have to 

consider vapor line length, configuration, canister 

effects, etc., in addition to vapor line diameter. 
-41-

have different performance characteristics 

different amount of activated carbon. 

and would require a 

In sizing the canister, the next step would be to estimate 

the total amount of activated carbon needed, based on gasoline 

vs. butane working capacity, apparent density, 

other factors. As is shown on Table 4, EPA 

carbon bed of 1050 grams would be required 

refueling emissions from an 18 gallon tank, 

density of 30 gm/100 ml, a canister of about 

would be needed. 

carbon aging and 

estimates that a 

to capture all 

At an apparent 

3500 milliliters 

Alternatively, however, EPA turned to work previously 

conducted by Mobil Research and Development in their 1978 

onboard demonstration program. In that program Mobil used a 

4350 ml canister to control refueling and evaporative emissions 

from a carburetted 1978 Pontiac Sunbird which had an 18.5 

gallon fuel tank.[l] An inquiry to Mobil revealed that the 

canister shell which is shown in Figure 13 was still on hand 

and available for loan, so this canister shell was used by EPA 

in the prototype system. This canister was loaded with 

approximately 1400 grams of activated carbon, somewhat more 

than needed based on Table 4. 

5. Conclusion 

We have now described all portions of the prototype 

onboard system used to evaluate the efficiency of the J-tube 

liquid seal. The prototype onboard system included the 

following components: 

J-tube liquid fillneck seal with reservoir 

18 gallon fuel tank 

fill limiter 

5/8 inch vapor line 

4350 ml activated carbon canister 

The results of EPA's evaluation testing on this system are 

described in the next portion of this report. 

B. Evaluation of System Efficiency 

1. Introduction 

Once the prototype onboard system had been constructed in 

a bench configuration, a series of refueling emissions tests 

were conducted to evaluate the efficiency of the system and to 
P.44 

-42-

Table 4 

Total Required Carbon Bed 

Refueling Emissions 144 g 

(at 8 g/gal for 18 gallons) 

Activated Carbon Needed: 700 g 

50 Percent Carbon Aging Allowance and 

Safety Factor 350 g 

Total 1050 g 

Based on a gasoline working capacity of 6.3 gm gasoline 

vapor/100 ml carbon, and an apparent density • of 30 gm 

carbon/100 ml carbon. 
- ^ — — — ^~ <

 m I 

FIGURE 13 

REFUELING SYSTEM CARBON CANISTER 

Carbon 

r^r^r r^rr [ 

m/m/l/M / / / / i/V 

ri^T^T^ 

Foam 

-ZZZZZZZZZZZZZZZZZ zzzzzz__rH Foam 

Wire Mesh 

Fiberglass Air Filter 

Sun bird Carburetor 

Bowl Fitting 

Chevrolet Carburetor 

Bowl Valves 

0.047" Bleed to Fuel Tank 

Side View of Top Disc 

n n—i - 1/8" Plexiglass 

1 " Dia. x l 3/4" Long 

Plexiglass Tube 

Wire Mesh Glued to Bottom of Tube 

of Tube 

Chevrolet Purge Valve, 

Drilled to 0.180" 

Canister Dimensions 

6" High 

8" Diameter 

Carbon: BPL-F3 

1550 Grams 

4350 ML 
-44-

draw some conclusions as to whether liquid seal systems could 

have as high an efficiency as mechanical seals. This portion 

of the report describes how these tests were done, the results 

of the testing, and draws some conclusions about the efficiency 

of liquid seal systems. 

2. Description of Test Procedure 

The refueling tests were conducted in a standard 

evaporative, emissions SHED which had been modified to allow the 

entry of a fuel hose fitting into the side wall. Fuel was 

dispensed from a standard fuel delivery cart. 

The general test procedure followed is outlined in 

Table 5, and is discussed below. The refueling control system 

bench system was placed in the SHED and filled to 10 percent of 

nominal tank capacity. The fuel tank was then heated to the 

desired temperature inside the open SHED with the fuel cap 

on.* The purge fan was operating in the SHED during this 

time. The dispensed fuel had been heated to its desired 

temperature previously. 

At the end of the heating, the heating blankets were 

unplugged, the fuel nozzle was inserted into the fillneck, the 

mixing fans were restarted, and the SHED was sealed. A 

background reading was taken in the sealed SHED before 

refueling began. The refueling was then performed by turning 

on the fuel cart from the outside the SHED. The refueling was 

terminated when automatic shut off occurred. A final FID 

reading was then taken in the SHED, and the SHED floor and 

fillneck area were checked for fuel spills. The refueling 

emissions to the SHED were evaluated as the difference between 

the initial and final FID readings, with appropriate 

adjustments for the small portion of the SHED volume occupied 

by the bench apparatus. 

Following the termination of the testing, the carbon 

canister was weighed and then purged with a total of 300 cfm of 

ambient air to remove refueling vapors from the canister. 

Based on reduction in canister weights, this amount of air was 

more than sufficient. Following completion of the purge, the 

canister'was weighed again. 

Finally, before describing the results of the testing, it 

is important to discuss the temperature and RVP characteristics 

As will be discussed later, a couple of tests were 

conducted with the fuel cap loose during the heat build to 

estimate the effects of heat build emissions. 
P.47 

-45-

Table 5 

Test Sequence 

1. Drain and refuel tank to 10 percent of nominal capacity, 

2. Connect heat blankets and thermocouples, fuel cap on. 

3. Heat tank to desired temperature and stabilize. 

4. Insert fuel nozzle, set latch at high level. 

5. Close SHED and start mixing fans. 

6. Take initial sample reading (using FID). 

7. Remove cap, refuel tank to automatic shut-off. 

8. Check for spills and nozzle shut-off. 

9. Take final sample reading (using FID). 

10. Disconnect, heat blankets and thermocouples. 
-46-

of the test fuels used. The dispensed and fuel tank 

temperatures were set at 92°F +_ 2°F to be consistent with 

previous testing conducted by EPA and to be representative of 

the temperature proposed by EPA in its recommended practice for 

testing of refueling emissions levels.[6,7] Fuels of 11.8 and 

9.0 psi RVP were used in the program. However most tests were 

conducted using the 11.8 RVP fuel since it would be expected to 

create higher refueling emissions and thus would be a more 

stringent evaluation of system efficiency. 

3 . Refueling Emission Test Results 

The results of the refueling emission tests are summarized 

in Table 6; more detailed information on each test is provided 

in Appendix A. The emission results shown include 7 tests at 

11.8 RVP and 3 tests at 9.0 RVP. 

The efficiency of the control system can be evaluated by 

comparing the refueling losses to the SHED to the total 

refueling emissions based on the sum of refueling losses to the 

SHED and canister weight gain. Under this approach the 

efficiency can be calculated as shown below: 

PFP = i _ losses.to SHED x 100% 

canister wt. gain + losses to SHED 

Using this approach, the average efficiency is 98 percent 

for the 11.8 psi fuel and 96.6 percent for the 9.0 psi fuel. 

Values ranged from 95.8 to 99.4 percent with an average of 

about 97 percent. However, these results clearly indicate that 

theoretical efficiencies of 98 percent or more are available 

for liquid seal systems. This compares to efficiencies of 

96-99 percent for a mechanical seal system.[1,8] 

As was noted previously, two tests were conducted with the 

fuel cap loose during the heat build to assess how much heat 

build emissions were affecting the total canister vapor load. 

Referring to Table 6, tests 1-5 were conducted with the fuel 

cap on and- fully sealed during the heat build, while tests 6 

and 7 were conducted with the cap only loosely in place. A 

comparison of the tests shows that the canister weight gain and 

the apparent refueling emission rate were greater when the cap 

was on and sealed. To some degree the canister was accepting 

vapor from the tank during the heat build similar to what now 

occurs in a diurnal evaporative emissions test. However, as 

can be seen from Table 6, this has little effect on the system 

efficiency evaluation for the program. All values fall within 

the 96-99 percent efficiency range. 
P.49 

RVP 

11.8 psi 

9.0 psi 

-47-

Test 

1 

2 

3 

4 

5 

6 

7 

Liquid 

Condi 

IT 

91.0 

90.8 

92.0 

91.0 

91.9 

92.0 

91.0 

Tabl 

Seal Control 

tions 

ID 

92.0 

90.3 

90.5 

91.7 

91.9 

92.0 

92.5 

Gal 

12.5 

15.5 

15.0 

15.1 

14.0 

15.5 

12.5 

e 6 

System Efficiencies 

Loss to 

SHED(q) 

2.3 

3.6 

6.1 

4.9 

2.5 

2.0 

1.5 

Canister 

Wt Gain(q) 

153.3 

168.1 

164.1 

129.3 

123.9 

170.5 

163.0 

Percent 

Efficiency 

99.4 

97.9 

96.4 . 

96.3 

98.0 

98.8 

99.1 

Avg. EFF 98. 0 

08 

09 

10 . 

92.0 

93.0 

92.0 

93.0 

92.2 

92.5 

18.5 

15.0 

15.0 

6.0 

3.6 

4.0 

135.5 

121.1 

120.8 

95.8 

97.1 

96.8 

Avg. EFF 96. 6 
-48-

The turbulent mixing in the fillpipe discussed previously 

and the subsequent entrainment of bubbles in the liquid 

entering the tank suggests that the liquid seal may be 

generating additional refueling emissions relative to the 

uncontrolled fuel tank. Uncontrolled refueling emissions were 

not evaluated on the bench system, but a similar fuel tank was 

evaluated on the 1983 Oldsmobile Cutlass evaluated in a 

previous EPA test program.[7] The results of that testing 

indicate that uncontrolled refueling emissions for this vehicle 

can be predicted using the equation 

Losses (g/gal) = -5.584 - 0.114[AT(°F)] + 0.0857 [TD(°F)] + 

0.520 [RVP(psi)], where AT = TT - TD. 

Substituting the temperature and RVP conditions of Table 6 

into this equation (TD = 92°F, AT = 0F°, RVP = 11.8 psi) 

yields an emission rate of 8.4 g/gal. 

For comparison, two tests were conducted on the prototype 

onboard system without the canister in place. The refueling 

emission rate averaged 9.9 g/gal for the two tests (Tests 

85-1363, 1364 in Appendix A). 

The comparison of the actually occurring and predicted 

emissions discussed above, leads to the conclusion that in this 

case the liquid seal increased the emission rate. However, 

using this data it is not .possible to precisely quantify the 

effect; the use of an average could be misleading due to the 

relatively small number of tests and the range in values seen. 

Ideally, comparisons should be made between identical tanks 

with and without a liquid seal with as many other variables as 

possible controlled. 

A close review of the detailed results in Appendix A 

reveals that 14-15.5 gallons was dispensed in most tests, but 

over 18 gallons was dispensed in one test. This later test was 

the first conducted in the series and led to the conclusion 

that the fill limiter installed in the tank did not work 

properly and an overfill occurred. However, when the fill 

limiter was modified and reinstalled it dropped too low into 

the tank and about a gallon of nominal tank capacity was lost. 

This accounts for the difference in the dispensed gallons among 

the tests, and explains why the amount of fuel dispensed in 

most tests was somewhat less than 90 percent of nominal tank 

capacity. 

4 . Source of Emissions 

In addition to assessing the control efficiency of the 

system, tests were also conducted to locate the source of 

refueling emissions from the control system. The first step in 

this process involved checking the fuel tank and vapor line for 
P.51 

-49-

leaks. This was done by removing the canister from the system, 

plugging the vapor line (at the canister end) and pressurizing 

the tank. A liquid was then applied to the tank and vapor line 

so that leaks could be seen. The system was free from leaks so 

the only possible sources of emissions were the fillneck and 

the canister (if breakthrough were occurring). In order to 

isolate the emissions from the fillneck, the canister was left 

off of the system and was replaced with a plastic vapor bag. 

Refueling operations were performed with the vapor bag in place 

and the refueling loss was measured. In this way, only the 

emissions from the fillneck were measured. The results from 

this set of tests are shown in Table 7. 

The refueling losses from the control system with the 

vapor bag are very similar to those emitted from the control 

system with the canister in place. The projected efficiencies 

shown in Table 7 were developed by dividing the refueling 

losses by the predicted emission level found using the equation 

cited previously. 

Since the refueling loss and efficiency numbers of Table 7 

are very similar to those in Table 6, it appears that most of 

the refueling loss comes from the fillneck. 

IV. Conclusions 

The purpose of the development and test programs conducted 

was to evaluate the practicality and feasibility of liquid 

fillneck seals as an alternative to the more widely 

demonstrated mechanical seals. The EPA program covered a 

laboratory evaluation of three different liquid seal concepts 

and bench testing of a simple prototype onboard system using a 

liquid seal. 

The evaluation of the liquid seal concept led to several 

conclusions. 

• The available fill height on most side fill 

passenger cars and light trucks is sufficient to 

permit the use of liquid seals without premature 

nozzle shut-off. 

• For some side fill vehicles, reductions in fill 

height would need to be achieved through internal 

fillpipe modifications to control the bubbles caused 

by the strong turbulent mixing in the fillpipe. 

• Rear fill vehicles would require more substantial 

fillpipe, tank, or other modifications to use liquid 

seals and thus may be better suited to mechanical 

seals. 
r 

-50-

Table 7 

Sources of Refueling Emissions on a Controlled System* 

Conditions Loss to Predicted Percent 

Test TT T D Gal. SHED(q) Emissions(q) Efficiency 

11 91.0 - 92.5 13.3 2.4 115.0 97.9 

12 91.0 92.5 13.5 2.8 116.8 97.6 

Vapor bag used to replace canister; RVP = 11.8. 
-51-

• Liquid seal systems (especially the J-tube and 

in-tube trap) appear to have safety advantages over 

the mechanical seal and submerged fill. 

• The strong turbulent mixing in the fillpipe entrains 

air into the fuel entering the tank, and increases 

the volume of vapor which is displaced from the tank 

as it is refilled. 

Several key conclusions can also be drawn from the bench 

testing of a prototype onboard system using a liquid seal. 

• The efficiency of the liquid seal systems is 

comparable to that achieved by mechanical seals. 

The mechanical seal systems evaluated by API showed 

efficiencies of 96 to 99 percent. The liquid seal 

systems evaluated in this project showed 

efficiencies in that range. 

• With improvements in the control system, 

consistently high control efficiencies (98 percent 

and greater) are easily within reach for. liquid seal 

systems. 

• For a liquid seal system with an adequately sized 

carbon canister, most refueling losses appear to 

arise from the fillneck. 

• The air entrainment caused by the turbulent mixing 

in the fillneck appears to increase the total 

refueling emissions load to the carbon canister. 

Data generated in this test program is insufficient 

to precisely quantify this effect. 

The primary purpose of this program was to demonstrate the 

feasibility of liquid fillneck seal concepts. The bench 

prototype developed here was clearly a first generation system; 

no attempts were made to optimize the design to reduce the 

effects of entrainment or to maximize control efficiencies. 

Improvements in both areas are possible, as demonstrated in 

later work conducted by API. [8] This work shows that onboard 

systems using liquid fillneck seals cah consistently control 

refueling emissions with efficiencies of 98 to 99 percent. 

The ' development and test programs conducted by EPA 

demonstrate that liquid seal systems are indeed practical 

alternatives to mechanical seal systems. Analysis suggests 

that liquid seals are superior to mechanical seals in the areas 

of durability, tampering, and safety, and have equal 

efficiencies for controlling refueling emissions. However, the 
P.54 

-52-

work conducted by EPA indicates that liquid seals may be more 

attractive for side fill than rear fill vehicles, and the air 

entrainment caused by turbulent mixing in the fillpipe may 

actually increase refueling emissions and create the need for a 

larger canister than that required for mechanical seals. Thus 

some trade-offs may exist between mechanical and liquid 

fillneck seals. 

Either liquid or mechanical fillneck seals could be used 

as part of - an onboard system. Each approach has its strengths 

and weaknesses, but both have been demonstrated to have high 

efficiencies on prototype systems. Whether a liquid or 

mechanical seal system is preferable would have to be evaluated 

separately for each vehicle model. 
-53-

References 

1. "On-Board Control of Refueling Emissions, 

Demonstration of Feasibility," Mobile Research and Development 

Corp., for American Petroleum Institute, Washington, D.C, 

October 2 1978. 

2. "Control of Refueling Emissions with an Activated 

Carbon Canister on the Vehicle - Performance and Cost 

Effectiveness Analysis," Olson Laboratories, Inc., for American 

Petroleum Institute, Washington, D.C, October, 1973. 

3. "SAE Recommended Practice (J 1045) - Instrumentation 

and Techniques for Vehicle Refueling Emissions Measurement." 

4. "Status of In-House Refueling Loss Measurements," 

Memorandum from Martin Reinemann to Robert Maxwell, U.S. EPA, 

SDSB, March 6, 1979. 

5. "Ford Motor Company Comments on the Evaluation of 

Air Pollution Regulatory Strategies for the Gasoline Marketing 

Industry," Nov. 1984. 

6. "Draft Recommended Test Procedure for the 

Measurement of Refueling Emissions," Lisa Snapp, EPA Technical 

Report, EPA-AA-SDSB-85-5, July, 1985. 

7. "Refueling Emissions from Uncontrolled Vehicles," D. 

Rothman and R. Johnson, EPA Report EPA-AA-SDSB-85-6, 1985. 

8. "Vehicle Onboard Refueling Control," API Publication 

4424, March 1986. 
P.56 

-54-

APPENDIX A 

Detailed Test Results 
Fuel Tank Bench Tests 

FUEL-COMMERCIAL UNLEADED, SUMMER, 92°F DISPENSED* 

^1 

Temperatures °F 

Test No. 

85-0694 

85-0120 

85-0121 

85-0123 

85-0698 

85-0699 

85-1358 

85-1362 

85-1368 

84-5633 

84-5634 

84-5635 

85-1363 

85-1364 

Date 

10-31-84 

11-05-84 

11-06-84 

11-07-84 

11-08-84 

11-09-84 

12-19-84 

01-04-85 

01-11-85 

08-23-84 

08-24-84 

08-24-84 

01-04-85 

01-03-85 

Initial 

66.8 

68."2 

68.3 

69.5 

67.55 

67.0 

61.0 

67.7 

60.5 

69.0 

67.0 

67.9 

70.7 

67.7 

Final 

91.0. 

91.0 

90.8 

91.0 

92.0 

91.0 

92.0 

91.0 

91.9 

92.0 

93.0 

92.0 

92.0 

92.5 

Final 

Vap 

89.0 

88.8 

89.0 

89.0 

90.0 

89.5 

88.5 

89.5 

91.0 

90.2 

89.0 

90.3 

89.0 

90.8 

Max 

T 

3.0 

3.0 

3.0 

3.5 

3.0 

3.0 

3.5 

3.0 

5.3 

2.0 

2.0 

2.0 

4.0 

3.0 

Dispensed 

92.0 

92.5 

90.3 

91.0 

92.0 

92.5 

90.5 

91.7 

91.9 

93.0 

92.2 

92.5 

89.8 

90.0 

Dispensed 

Gallons 

12.5 

13.3 

15.5 

13.5 

15.5 

12.5 

15.0 

15.1 

14.0 

18.5 

15.0 

15.0 

14.3 

14.5 

Refueling 

Loss, 

gms. 

2.3 

2.4 

3.6 

2.8 

2.0 

1.5 

6.1 

4.9 

2.5 

6.0 

3.6 

4.0 

134.8 

151.5 

Canister 

Wt Gain 

153.3 

NA 

168.1 

NA 

170.5 

163.0 

164.1 

129.3 

123.9 

135.5 

121.1 

120.8 

NA 

NA 

Dispensing 

Time 

Min,Sec 

1'46" 

2'04" 

2'11" 

1'57" 

2'19" 

1'49" 

2'16" 

2'08" 

2'50" 

3'41" 

2'56" 

2'55" 

2'00" 

2'09" 

Heat 

Time 

Mr,Min 

57" 

52" 

56" 

45" 

51" 

55" 

58" 

40" 

45" 

46" 

48" 

48" 

56" 

42" 

Spillage/Comments 

None 

None, vapor bag 

None, manual shutoff 

None, vapor bag 

None, can in box 

multi-fueling 

None, multi fueling 

None, Benzene 13A 

Controlled 

None, canister only 

during refueling 

None 

None, manual shutoff 

None, manual shutoff 

Controlled w/o canister 

Controlled w/o canister 

All tests were at 11.8 RVP except 84-5633, 5634, and 5635.