Guide pole fitting seal for floating roof storage tanks

A guide pole fitting seal for use on floating roof tanks that incorporates a well gasket, pole sleeve, pole wiper, float and float wiper that may be used with guide poles to control emissions from the guide pole fitting. The guide pole seal may permit the product level in the tank to be measured and sampled from inside of the guide pole by removing the float during these operations.

BACKGROUND OF THE INVENTION 
The present invention relates generally to floating roof tanks and more 
specifically to methods and apparatus for sealing the guide pole opening 
in the floating roof to reduce emissions of vapor from the tank. 
Ambient air quality has become an increasingly important concern in recent 
years. Many air pollutant emission sources that were tolerated in years 
past are now facing regulations which force significant reductions or 
elimination of such emissions. One category of such emission sources is 
aboveground storage tanks for the storage of volatile liquids. 
Although there are other types of aboveground storage tanks for the storage 
of volatile liquids, one type of such tank in wide use is referred to as 
an external floating-roof tank. This type of tank has a circular 
essentially flat bottom, a vertical cylindrical shell having a lower edge 
joined to the tank bottom and an external floating roof adapted to float 
on the volatile liquid stored in the tank. The rim space, which is located 
between the floating roof rim and the inside surface of the tank shell, is 
sealed by one of several rim sealing means attached to and movable 
vertically simultaneously with the floating roof so as to reduce emissions 
to the atmosphere from the rim space. Some such seals are disclosed in the 
U.S. Pat. Numbers: Moyer U.S. Pat. No. 2,829,795; Harris et al. U.S. Pat. 
No. 2,968,420; Reese U.S. Pat. No. 3,075,668; Wissmiller U.S. Pat. No. 
3,120,320; Moyer U.S. Pat. No. 3,136,444; and Bruening U.S. Pat. No. 
4,406,377. 
The floating roof moves vertically upward when the storage tank is filled 
with product, and moves vertically downward when product is withdrawn from 
the storage tank. Although the external floating roof is permitted to move 
in a vertical direction and, to a lesser extent, in a radial direction, it 
is necessary to provide guides to prevent rotation of the floating roof so 
as to prevent damage to other appurtenances on the floating roof such as 
rolling ladders, rainwater drain systems, and automatic level gauges. 
To prevent rotation of the floating roof, a guide pole is commonly used. 
The guide pole is located inside of the storage tank near the tank shell 
and is fixed at the bottom to the tank bottom and is fixed at the top to 
the top of the tank shell. The guide pole penetrates the floating roof 
through a guide pole fitting, which results in a source of emissions to 
the atmosphere. 
Gauging the product liquid level in the storage tank or obtaining samples 
of the product in the storage tank has been done utilizing the interior of 
the guide pole. To facilitate gauging and sampling operations, the guide 
pole is hollow and has openings to allow the product inside of the guide 
pole to freely mix with product outside of the guide pole so that the 
composition and liquid level inside of the guide pole are the same as that 
outside of the guide pole in the storage tank. These openings are often in 
the form of vertical columns of slots which overlap on alternating rows so 
that at any vertical position there is always communication between the 
liquid within the guide pole and the liquid outside of the guide pole. 
The wind has been found to have an important effect in causing emissions 
from certain types of roof fittings and wind tunnel tests have been 
performed to measure the emission loss factors of different types of 
floating roof fittings, including guide pole fittings. A wind tunnel 
simulated the flow of atmospheric air over the floating roof fittings, as 
occurs on external floating roofs, and revealed that the guide pole 
fitting had the highest emissions of all of the fittings tested. In fact, 
one type of commonly used guide pole fitting had emissions that were about 
25 times the emissions from the entire rim seal of an external floating 
roof. 
Therefore, it is desirable to incorporate emission control features in 
guide pole fittings to reduce the emission loss factors. 
SUMMARY OF THE INVENTION 
According to the present invention, a guide pole fitting seal is provided 
for a tank having a floating roof and a guide pole well in the floating 
roof defining an opening through which a guide pole extends, the guide 
pole fitting seal including a well gasket supported by the guide pole 
well, a sliding cover supported by the well gasket, the sliding cover 
defining an opening through which the guide pole extends, a pole sleeve 
joined to and extending downwardly from the sliding cover to at least the 
level of product stored in the tank, the pole sleeve defining a bore 
through which the guide pole extends, and a pole wiper joined to the 
sliding cover in wiping engagement with the guide pole. There may also be 
a float having means for floating on liquid product within the guide pole 
when it has openings through which liquid product circulates, and a float 
wiper joined to the float and in wiping engagement with the inside of the 
guide pole. 
There may also be a fixed cover joined to the guide pole well which 
supports the well gasket, the fixed cover also defines an opening through 
which the slotted pole extends. 
To minimize the load on various seal elements, a guide may be provided that 
carries some of the load of the floating roof as it tends to rotate. The 
guide may include a roller assembly that consists of a separate roller on 
each side of the guide pole with the axis of the roller oriented parallel 
to the radius from the center of the floating roof to the center of the 
guide pole. 
To maintain contact between the well gasket and the sliding cover, a 
retainer attached to the floating roof may be used. In one embodiment, a 
retainer angle may be joined to each sliding cover guide angle to define a 
slot parallel to the radius from the center of the floating roof to the 
center of the guide pole to permit radial sliding of the sliding cover 
while maintaining contact between the sliding cover and the well gasket. 
The pole sleeve has been found to be an important element in controlling 
emissions from guide pole fittings and particularly important when used 
with slotted guide poles because it blocks wind driven air that would 
otherwise pass between the fixed cover and the sliding cover into the well 
vapor space, mix with product vapor, flow into the guide pole through the 
exposed vapor space openings, flow upward and exit through the openings in 
the guide pole that are above the sliding cover. The guide pole sleeve has 
been found to be very effective in reducing emissions when it is used in 
combination with the other emission control features that are part of this 
invention, resulting in a roof fitting loss factor of 106 pound-moles per 
year at an ambient wind speed of 10 miles per hour, as compared to a roof 
fitting loss factor of about 5000 pound-moles per year at the same wind 
speed for a guide pole fitting which does not incorporate these emission 
control features. Flexible guide pole sleeves may be installed in existing 
tanks through the guide pole hole in the sliding cover without taking the 
tank out of service. 
The roller assembly may be used in combination with the emission control 
features to facilitate vertical movement of the floating roof while 
restraining rotation of the floating roof about its vertical axis. The 
roller assembly also withstands most of the rotational forces that could 
otherwise damage the pole wiper and pole sleeve, and impair their ability 
to properly seal the space between the outside surface of the guide pole 
and the inside surface of the pole sleeve.

DETAILED DESCRIPTION OF THE INVENTION 
To the extent that it is reasonable and practical, the same elements which 
appear in the various drawing figures will be identified by the same 
numbers. 
FIG. 1 illustrates a portion of an external floating roof tank 20. The tank 
20 includes a flat circular bottom 22 resting on a suitable foundation 24 
above ground level. A vertical cylindrical tank shell 26 is joined to the 
bottom 22 and extends upwardly. A floating roof 30 is positioned inside 
the tank shell 26 such that it floats on top of liquid product 32 within 
the tank 20 and defines a roughly annular rim space 34 around its outer 
vertical rim 36. 
The annular rim space 34 is substantially sealed using any conventional rim 
seal system that may include a mechanical or resilient, primary seal 38 
and an optional wiping, secondary seal 40. The primary seal 38 and the 
secondary seal 40 reduce vapor emissions from the annular rim space 34 
around the floating roof 30 and permit limited radial movement of the 
floating roof but provide little resistance to rotational movement. 
The floating roof 30 can be of any conventional construction, but typically 
includes an upper deck 44 and a lower deck 46 which are joined by vertical 
support plate 48 and the vertical rim 36 to define an enclosed space that 
aids in adding buoyancy to the floating roof 30. The lower deck 46 floats 
in direct contact with product 32 and the upper deck 44 provides a 
platform for supporting workmen and equipment. 
External floating roof tank 20 can be used to store a wide variety of 
volatile liquid products 32 such as gasoline, jet engine fuel, kerosene, 
and other highly volatile liquid hydrocarbons, many of which become 
combustible when mixed with the right amount of air. 
The present invention is also useful in reducing the evaporation loss of 
stored product even when used with internal floating roof tanks which have 
a fixed roof positioned over a floating roof. 
The floating roof 30 moves vertically during tank filling and emptying 
operations, but its rotation about a vertical axis must be limited to 
prevent damage to certain external floating roof tank 20 components, such 
as the rim seal system 38 and 40, automatic level gauging devices, rolling 
ladders that extend from the top of the tank shell 26 to the top of the 
external floating roof 30, and floating roof rain water drainage systems. 
To prevent rotation of the external floating roof 30, a guide pole 60 is 
used which rests on lower supports 66 and is secured a gauger's platform 
68 at an upper support 67. The guide pole 60 penetrates the external 
floating roof 30 at a guide pole fitting 64 which is illustrated in FIG. 1 
in accordance with the present invention. 
In addition to preventing rotation of the floating roof 30, the guide pole 
60 is often used to sample and determine the liquid level of the product 
32 in the storage tank 20. In order to obtain representative samples or 
determine accurate product levels of product 32 inside of the tank 20, the 
guide pole 60 commonly incorporates openings 70 to permit free 
communication of the product 32 in the storage tank 20 with that portion 
of the product 32 inside of the guide pole 60. A gauge hatch 72 is 
provided at the top of the guide pole 60 to permit the tank gauger to 
sample and gauge the product 32 inside of the guide pole 60. 
One method of providing openings 70 in a guide pole 60 involves the use of 
vertical columns of slots, where the slots 70 in the various columns are 
spaced apart around the circumference of the guide pole 60, and vertically 
overlap as illustrated in FIG. 2 to provide continuous communication of 
the product 32 inside the guide pole 60 with the product 32 inside of the 
storage tank 20 at all levels within the tank 20. Other shapes and 
arrangements of guide pole openings 70 can be used with the present 
invention. 
A typical guide pole fitting includes a vertical cylindrical guide pole 
well 80 that defines a bore through which guide pole 60 extends, and that 
defines a well vapor space 82. The guide pole well 80 need not extend 
upward beyond, and may be flush with, the upper deck 44 of floating roof 
30. On top of the guide pole well 80 there is welded a fixed cover 84 that 
provides an upper horizontal bearing surface on which a sliding cover 86 
rests. The fixed cover 84 defines an elongated hole 88 (See: FIG. 4) with 
a longitudinal axis that is substantially parallel to the radius that 
extends from the center of the floating roof 30 to the center of the guide 
pole 60. The elongated hole 88 permits the floating roof 30 to move 
radially but not rotationally. The sliding cover 86 defines a hole 89 that 
is roughly the same shape as the guide pole 60 (illustrated as circular in 
FIG. 4) so that the sliding cover 86 is maintained adjacent to the guide 
pole 60 and yet is free to move vertically along the guide pole 60. As the 
floating roof 30 moves radially in and out from the center of the tank 20, 
fixed cover 84 slides under sliding cover 86 and the floating roof 30 is 
restrained from rotation by the guide pole 60 bearing on the guide pole 
fitting 64. 
The use of a guide pole 60 having openings 70 and that penetrates the 
external floating roof 30 through a guide pole fitting, however, has been 
found to cause a large rate of atmospheric emissions. FIG. 2 illustrates a 
type of guide pole fitting construction 90 that has been commonly used on 
external floating-roof tanks 20. It includes a guide pole well 80, a fixed 
cover 84, and a sliding cover 86 similar to some of the basic components 
of the guide pole fitting 64 illustrated in FIG. 1. Wind-tunnel tests have 
been conducted on guide pole fittings 90 of the type illustrated in FIG. 2 
to determine their evaporative loss or atmospheric emission 
characteristics. These test results were used to prepare American 
Petroleum Institute (API) Publication 2517, "Evaporative Loss from 
External Floating-Roof Tanks," 3rd Edition, February 1989. This 
publication describes the method for calculating evaporative loss from 
floating roof fittings. The loss from each type of floating roof fitting 
may be calculated using Equation 1: 
EQU L.sub.f =K.sub.f P* M.sub.v K.sub.c (Equation 1) 
where: 
L.sub.f =evaporative loss from the type of roof fitting being considered, 
in pounds per year; 
K.sub.f =roof fitting loss factor, in pound-moles per year; 
P*=vapor pressure function (dimensionless); 
M.sub.v =average stock vapor molecular weight, in pounds per pound-mole; 
and 
K.sub.c =product factor (dimensionless). 
In Equation 1, the roof fitting loss factor, K.sub.f, depends only upon the 
construction features of the floating roof fitting and upon the ambient 
wind speed. The other factors in Equation 1 depend upon the 
characteristics of the stored product and are independent of the type of 
floating roof fitting being considered. Thus, to compare the evaporative 
loss control of different types of floating roof fittings, it is only 
necessary to compare their roof fitting loss factors, K.sub.f. 
Table A lists the roof fitting loss factors, K.sub.f, at ambient wind 
speeds of 5, 10 and 15 miles per hour of 9 different types of roof 
fittings commonly used on external floating roofs. 
TABLE A 
______________________________________ 
Roof Fitting Loss Factors, K.sub.f (pounds-moles per year), 
for Various Roof Fitting Types and Construction Details 
Roof Fitting Loss Factor K.sub.f 
Fitting Wind Wind Wind 
Num- Roof Fitting Type and 
Speed Speed Speed 
ber Construction Details 
5 m.p.h. 10 m.p.h. 
15 m.p.h. 
______________________________________ 
1 ACCESS HATCH 0 0 0 
Bolted Cover, 
Gasketed 
2 RIM VENT 1.21 1.71 2.21 
Weighted Actuation, 
Gasketed 
3 GAUGE-HATCH/ 1.65 2.35 3.05 
SAMPLE WELL 
Weighted Actuation, 
Gasketed 
4 VACUUM BREAKER 2.05 2.90 3.75 
Weighted Actuation, 
Gasketed 
5 ROOF LEG 2.50 3.50 4.50 
Adjustable, Pontoon 
Area 
6 GAUGE-FLOAT 31.8 61.3 90.8 
WELL 
Unbolted Cover, 
Ungasketed 
7 OVERFLOW ROOF 66.6 176 310 
DRAIN 
Open 
8 GUIDE POLE 324 640 952 
FITTING 
Unslotted Guide Pole, 
Sliding Cover, 
Ungasketed 
9 GUIDE POLE 2,139 4,913 7,992 
FITTING 
Slotted Guide Pole, 
Sliding Cover, 
Ungasketed 
______________________________________ 
The roof fitting loss factors listed in Table A are based upon the values 
contained in API Publication 2517, which was mentioned above. Table A 
illustrates the fact that guide pole fittings have the highest roof 
fitting loss factors. In particular, guide poles that contain openings or 
slots for the purpose of tank gauging and product sampling have the 
highest loss factors listed in Table A. For example, at an ambient wind 
speed of 10 miles per hour, a slotted guide pole fitting has a roof 
fitting loss factor of 4,913 pound-moles per year. In comparison, at an 
ambient wind speed of 10 miles per hour, the roof fitting loss factor for 
the entire rim seal on an external floating-roof tank that is 100 foot in 
diameter would be only about 200 pound-moles per year when a double rim 
seal system is used, which is a rim seal system that consists of a 
combination primary rim seal and secondary rim seal. Thus, the roof 
fitting loss factor for the slotted guide pole fitting is about 25 times 
that from the entire floating roof rim seal system. This comparison 
highlights the importance of incorporating more effective emission control 
construction features in guide pole fittings. 
The wind tunnel tests that were performed to measure the roof fitting loss 
factors of guide pole fittings also revealed the mechanisms involved in 
evaporative loss from guide pole fittings of the construction illustrated 
by FIG. 2. Air flows across the guide pole fitting 90 are represented by 
arrows and illustrate how air enters the well vapor space 82 by flowing 
between any gap present between the fixed cover 84 and the sliding cover 
86 on the upwind side of the guide pole fitting 90. This air then mixes 
with product 32 vapor in the well vapor space 82 and exits through a 
combination of the three paths illustrated in FIG. 2. First, air laden 
with product vapor exits the well vapor space 82 through gaps between the 
fixed cover 84 and the sliding cover 86 on the downwind side of the guide 
pole fitting 90. Second, air laden with product vapor exits the well vapor 
space 82 through gaps between the sliding cover 86 and the guide pole 60 
on the downwind side of the guide pole fitting 90. Third, air laden with 
product vapor flows into the guide pole slots 70 that are exposed to the 
well vapor space 82, flows vertically upward inside the slotted guide pole 
60, and exits the slots 70 that are located above the sliding cover 86. 
Based on this understanding of the evaporative loss mechanisms from 
previous slotted guide pole fittings 90, novel evaporative loss control 
construction features of the present invention were incorporated into the 
guide pole fitting 64 (illustrated in FIGS. 1 and 3 through 9) to reduce 
the evaporative loss rate. These features include a well gasket 100, a 
pole sleeve 102, a pole wiper 104, a float 106, and float wipers 108. When 
these emission control construction features are used in combination, as 
illustrated in FIG. 3, a significant reduction occurs in the roof fitting 
loss factor, K.sub.f, for the slotted guide pole fitting 64. 
Table B lists the roof fittings loss factors, K.sub.f, of guide pole 
fittings that incorporate these evaporative loss control features at wind 
speeds of 5, 10 and 15 miles per hour. In Table B, Fitting Number 1 is 
listed for comparison, since it does not incorporate any of the 
evaporative loss control features that are part of this invention. In 
Table B, Fitting Number 5 incorporates all of the evaporative loss control 
features that are part of this invention and results in a roof fitting 
loss factor of 106 pound-moles per year at a wind speed of 10 miles per 
hour. This is a reduction in the roof fitting loss factor of 98 percent 
from the roof fitting loss factor for Fitting Number 1 in Table B, 
illustrating the effectiveness of these emission control features when 
incorporated in a guide pole fitting 64. 
TABLE B 
__________________________________________________________________________ 
Roof Fitting Loss Factors, K.sub.f, (pound-moles per year) 
for Guide Pole Fittings Used With Slotted Guide Poles 
Guide Pole Fitting Description 
Roof Fitting Loss Factor K.sub.f 
Fitting 
Well Float 
Pole 
Pole 
Wind Speed 
Wind Speed 
Wind Speed 
Number 
Gasket 
Float 
Wiper 
Sleeve 
Wiper 
5 m.p.h 
10 m.p.h. 
15 m.p.h. 
Notes 
__________________________________________________________________________ 
1 No No No N/A N/A 2139 4913 7992 1 
2 Yes No No N/A N/A 1794 4121 6703 1 
3 No Yes Yes N/A N/A 725 2900 6525 1 
4 Yes Yes Yes N/A N/A 405 2135 5650 1 
5 Yes Yes Yes Yes Yes 55 106 156 2 
__________________________________________________________________________ 
Notes: 
1 The loss factors of Fitting Nos. 1 through 4 are from the American 
Petroleum Institute, Publication 2517, "Evaporative Loss from External 
FloatingRoof Tanks", Third Edition, February 1989. 
2 These loss factors were measured in a wind tunnel on a guide pole 
fitting constructed in accordance with this invention. 
FIGS. 3 and 4 illustrate a guide pole fitting 64 that incorporates all of 
the emission control features of the present invention, namely: a well 
gasket 100 located between the fixed cover 84 and the sliding cover 86; a 
pole sleeve 102 completely surrounding the guide pole 60 and extending 
downward from the sliding cover 86 into the liquid product 32; a pole 
wiper 104 attached to the sliding cover 86 and extending over the space 
between the outside surface of the guide pole 60 and the inside surface of 
the pole sleeve 102, and in continuous wiping contact with the outside 
surface of the slotted guide pole 60 in the area adjacent to the pole 
wiper 104; a vertical cylindrical float 106 that is contained inside the 
slotted guide pole 60 and which floats in the product 32 that is contained 
within the slotted guide pole 60, effectively reducing the amount of 
exposed product 32 liquid surface area within the slotted guide pole 60; 
and at least one float wiper 108 which is attached to the float 106 and is 
in continuous wiping contact with the inside surface of the slotted guide 
pole 60, effectively covering the gap between the inside surface of the 
guide pole 60 and outside surface of the float 106. 
The wiping contact of the pole wiper 104 and the float wipers 108 provides 
an effective vapor seal that also wipes clingage of liquid product off of 
the guide pole 60 that could otherwise be exposed to the atmosphere when 
the floating roof 30 descends. Once exposed to the atmosphere, the 
clingage evaporates and results in a loss of valuable product. 
The floating roof tank 20 may be used to store volatile liquid products 
that are flammable, and are therefore combustible when mixed with air. To 
avoid combustion, it is desirable to use materials in the guide pole 
fitting seal that are not likely to cause a spark as they move past one 
another. Thus, the sliding cover 86 and the pole sleeve 80 are preferably 
made of stainless steel, brass, or aluminum. 
The pole sleeve 102 may be made of metal, plastic or fabric so long as it 
does not hang up on the guide pole 60 during vertical or radial movement 
of the floating roof 30 and functions to block the flow of wind around the 
guide pole 60 to reduce the emissions that result from the wind flow as 
illustrated in FIG. 2. 
Flexible pole sleeves may be particularly useful in retrofitting existing 
tanks with that feature of the invention. This may be accomplished in some 
installations without taking the tank 20 out of service by simply 
inserting the flexible pole sleeve 80 down the annular space between the 
outside surface of the guide pole 60 and the inside edge of the hole 89 in 
the sliding cover 86 into the stored product 32 and securing it to the 
sliding cover 86. The flexible sheet material may be a non-metallic 
material similar to that used for the wipers and gaskets or it may be a 
resilient sheet of plastic or metal. 
The fixed cover 84 provides a convenient horizontal bearing surface for the 
well gasket 100, but it is optional and could be omitted and replaced by 
the flat surface of the upper deck 44 of the floating roof 30 or the well 
gasket 100 could be positioned on the top of the guide pole well 80 and 
secured by any conventional means. 
The well gasket 100, pole wiper 104 and float wiper 108 must be constructed 
of materials that are compatible with the chemical characteristics of the 
product 32. The material used must be selected to provide durability under 
the expected operating conditions. In particular, the pole wiper 104 and 
float wiper 108 material must have sufficient abrasion resistance to 
permit continued operation over the desired life of the guide pole fitting 
64 prior to maintenance work. For a wide range of petroleum products, 
Chloroprene (Neoprene), Acrylonitrile-Butadiene Poly Vinyl Chloride 
(Buna-N/Vinyl), Hypalon, Polyurethane, and Fluorelastomer (Viton) are 
acceptable seal and gasket materials. Also useful are durable materials 
made of fiber or fabric reinforced plastics such as Neoprene on Nylon 
fabric, Polyurethane on Nylon or Polyester fabric, Buna-N/Vinyl on Nylon 
fabric, or Viton on Nylon fabric. One other suitable material is made of 
Viton on one side and Buna-N/Vinyl on the other side of Nylon fabric. It 
should be understood that the seals and gaskets function to prevent a 
substantial amount of emission loss, but are not absolute in their sealing 
ability. 
The float 106 may be fabricated from a metal cylinder with closed ends, 
with an empty interior space that results in a weight appropriate for 
floating in the intended product 32. Alternatively, the float 106 may be 
fabricated of a non-metal cylinder with closed ends, such as Polyurethane 
or Polyethylene, with the interior left empty or filled with a closed cell 
polymeric foam material, such as Polyurethane foam. At least one float 
wiper 108 may be used to provide a seal between the inside surface of the 
guide pole 60 and the outside surface of the float. A plurality of float 
wipers 108 may also be used to provide a more effective seal between the 
inside surface of the guide pole 60 and the outside surface of the float 
106. A cable 120 is attached to the top of the float 106 and extends 
vertically upward to the top of the guide pole 60 to permit removal of the 
float 106 during product 32 gauging or sampling operations. 
During tank filling and emptying operations, the floating roof 30 rises or 
descends, respectively, to accommodate the change in volume of the stored 
product 32. It is important that the forces transmitted by the floating 
roof 30 to the guide pole 60 not interfere with the proper operation of 
the pole sleeve 102 or pole wiper 104. Therefore, a guide, such as a 
roller assembly 130, can be used to help control the rotational forces of 
the floating roof 30 on the pole sleeve 102 and pole wiper 104 and to 
transmit these forces instead to the fixed cover 84 or to the floating 
roof 30. The roller assembly 130 includes rollers 162, roller support 
plates 164, and roller shaft bushings 166. The roller support plates 164 
are connected to the sliding cover retainer angles 200 in a manner that 
permits rotation of the rollers 162 as the floating roof 30 rises or 
descends. The rollers 162 are oriented so that the axis of the rollers is 
horizontal and parallel to the radial line that extends from the center of 
the floating roof 30 through the center of the guide pole 60. The openings 
70 in the guide pole 60 are preferably located in areas of the guide pole 
60 where contact between the rollers 162 and the guide pole 60 does not 
occur so as to permit better transmission of forces between the guide pole 
60 and the rollers 162. For example, the openings 70 may be located on the 
radial line that extends from the center of the floating roof 30 through 
the center of the guide pole 60, as illustrated in FIG. 4. 
For some floating roof storage tanks 20, an alternative floating roof guide 
may be used to control rotation of the floating roof 30. In these cases, 
the slotted guide pole 60 may be used primarily for measuring the product 
32 level and sampling the product 32, and the roller assembly 130 may not 
be required to control the rotation of the floating roof. 
There are at least three methods for connecting the pole sleeve 102 to the 
sliding cover 86 and they are illustrated in FIGS. 5, 7 and 8. In FIG. 5, 
the pole sleeve 102 is shown to be connected to the sliding cover 86 by 
means of a welded or brazed joint. The sliding cover 86 is permitted to 
slide only in a radial direction from the center of the floating roof 30 
and is restrained from moving in other directions by the use of the 
sliding cover guide angles 170 which are attached to the fixed cover 84 on 
either side of the sliding cover 86. The sliding cover guide angles 170 
may be attached to the fixed cover 84 by means of welding. 
Also illustrated in FIG. 5 is a float 106 (shown in phantom lines) having a 
float wiper 108 above the pole wiper 104 which may provide additional 
sealing when used with a float wiper 108 near the level of the liquid 
product 32 in the tank 20, but which may actually increase emissions if 
not used with a float wiper 108 below the pole wiper 104 because it 
directs wind down into the hollow guide pole 60 and into contact with the 
product 32. Therefore, it is desirable to avoid using only one float wiper 
108 which is positioned above the pole wiper 104. 
FIG. 7 illustrates a second method of connecting the pole sleeve 102 to the 
sliding cover 86 that involves the use of a bolted connection on the 
bottom side of the sliding cover 86. The pole sleeve 102 is equipped with 
a flange 182 to permit the use of bolts 184 and nuts 194 to connect the 
pole sleeve 102 to the sliding cover 86. 
FIG. 8 illustrates a third method of connecting the pole sleeve 102 to the 
sliding cover 86 that involves the use of a bolted connection on the top 
side of the sliding cover 86. The pole sleeve 102 is equipped with a 
flange 182 to permit the use of studs 192 and nuts 194 to connect the pole 
sleeve 102 to the sliding cover 86. With this method of connection, it is 
advisable to use a pole sleeve gasket 196 that is located between the top 
surface of the sliding cover 86 and the bottom surface of the pole sleeve 
flange 182. 
FIGS. 5, 7 and 8 also illustrate three methods of attaching the pole wiper 
104 to the sliding cover 86. FIG. 5 illustrates placement of the pole 
wiper 104 on the top surface of the sliding cover 86. A pole wiper 
retainer plate 197, studs 193 attached to the sliding cover 86, and nuts 
194 are used to attach the pole wiper 104 to the sliding cover 86. 
FIG. 7 illustrates a second means of attaching the pole wiper 104 to the 
sliding cover 86 that is similar to the means that is illustrated in FIG. 
5, with the difference that bolts 184 are used instead of studs 193. 
FIG. 8 illustrates a third means of attaching the pole wiper 104 to the 
sliding cover 86. In this arrangement, the pole wiper 104 rests on the top 
surface of the pole sleeve flange 182. The pole wiper 104 is held in place 
with pole wiper retainer plate 197, studs 192 attached to the sliding 
cover 86, and nuts 194. 
FIG. 6 illustrates one means for mounting the rollers 162 on the guide pole 
fitting 64. Sliding cover retainer angles 200 are attached to the sliding 
cover guide angles 170 with bolts 202 and nuts 204. The sliding cover 
retainer angle 200 defines a sliding recess in which sliding cover 86 is 
permitted to move in a radial direction relative to the center of the 
floating roof 30, but prevents the sliding cover 86 from moving vertically 
off of the top surface of the well gasket 100. The retainer angle 200 need 
not be in constant contact with the sliding cover 86 so long as the 
sliding cover 86 is prevented from lifting off the well gasket 100 as the 
floating roof 30 descends. At other times, the weight of the sliding cover 
86 is sufficient to maintain contact with the well gasket 100. 
A roller support plate 164 may be attached to the sliding cover retainer 
angle 200 by welding or other suitable methods. Circular brass bushings 
166 are located in the roller support plates 164 to accommodate the shaft 
210 of the rollers 162. The rollers 162 may be fabricated of stainless 
steel, brass or other suitable material that minimizes the generation of 
sparks. The rollers may be made of carbon steel. 
FIG. 9 is a plan view of the top surface of the fixed cover 84, which 
defines elongated opening 88 to permit vertical passage of the guide pole 
60. The width of the opening 88 is somewhat larger than the outside 
diameter of the guide pole 60. The opening 88 is elongated in the radial 
direction from the center of the floating roof 30 to permit some radial 
movement of the floating roof 30 relative to the guide pole 60. The well 
gasket 100 may be cut to the shape illustrated in FIG. 9 so as to 
completely surround the opening 88, yet fit between the sliding cover 
guide angles 170. The well gasket 100 may be attached to the top surface 
of the fixed cover 84 with a suitable adhesive 212, as illustrated in 
FIGS. 5, 6, 7 and 8. 
The foregoing detailed description has been given for clearness of 
understanding only, and no unnecessary limitation should be understood 
therefrom, as modifications will be obvious to those skilled in the art.