Device for measuring the static pressure of a moving fluid

A directional device operating similar to a wind vane has a hollow vertical shaft which is journalled in a housing containing three chambers in communication. An air inlet port is located on the side of the directional vane and communicates through the hollow journalled shaft into the first chamber. A small aperture in the wall between the first and second chambers dampens the movement of the fluid flow from chamber 1 to chamber 2. A conventional baffle separates the second and third chambers and simultaneously allows fluid flow from the second to the third chamber while further damping the fluid flow to such a point that the fluid in the third chamber is substantially static. The third chamber is in communication with a differential pressure gauge which then compares the static pressure in chamber 3 with another pressure source. Because the air inlet port is always maintained perpendicular to the wind direction, pulsations and surges of air pressure through the air inlet port caused by wind shifts are greatly reduced, and the fluid is damped twice before entering the third chamber as a static fluid.

BACKGROUND OF THE INVENTION 
Offshore petroleum operations frequently employ a shack or shed on the 
drilling/production platform which houses any number of machines, 
equipment and other electrical devices necessary for the maintenance, 
operation and safety of the drilling platform. Any number of inflammable 
hydrocarbon vapors are present on the drilling/production rig and can 
easily be ignited or combusted by electrical arcing, cigarette lighting or 
welding operations. In an attempt to eliminate the above-mentioned fire 
hazards, it has become common practice to maintain the interior of the 
shed housing the equipment and machinery at a pressure greater than the 
pressure outside the shack. Therefore, the greater pressure inside the 
shack insures that none of the inflammable vapors can enter into the shack 
and thereby become combusted or inflamed. 
In an attempt to increase further the safety of the drilling platform 
environment, an automatic shut-off switch to all the associated machinery 
has been connected to a differential pressure gauge such that when the 
pressure inside the shack relative to that outside the shack is reduced 
below a certain level, for example equal to that of the outside pressure, 
all the associated equipment is immediately cut off. In order to compare 
accurately the pressure inside the shack with that outside the shack, 
static pressure must be measured in both instances. In the past, static 
air inlet ports have been projected from within the shack through the roof 
or wall thereof in order to communicate with the outside environment. 
Consequently, in a no wind situation accurate readings are obtained. The 
presence of a wind, however, causes the sum of both the dynamic and static 
pressures to be read erroneously as static pressure. If a wind develops 
such that the static air port is on the upwind side of the shack, the 
actual pressure measured is greater than the true static pressure inasmuch 
as both static and dynamic pressures are being read on the pressure gauge. 
A false alarm arises, because the outside pressure is erroneously read 
high, thus reducing the measured ratio of the inside pressure to the 
outside pressure to a smaller fraction and giving a false "low inside 
pressure" reading. Periods of up to three hours are frequently required to 
reactivate all the equipment which has needlessly been cut off. 
Similarly, if the static air port is located downwind, a low pressure area 
surrounding the static air port frequently occurs and pressures lower than 
the true static pressure will be read outside the shack. In such a 
situation the denominator (outside pressure) is reduced thereby increasing 
the ratio of inside to outside pressure. Accordingly, the actual inside 
pressure can fall below the safe level and produce a hazardous situation. 
SUMMARY OF THE INVENTION 
The present invention employs a directional device operating on a principle 
similar to a weather vane. A static air port is located on an elongated 
member which has fins at one end and an adjustable weight on the other 
end. Accordingly, the elongated member, or wind vane, tends to remain 
aligned parallel to the wind direction irrespective of any wind shifts. 
Similarly, the static port tends to remain at a constant angle relative to 
the wind direction thereby eliminating pulsations and surges of wind on 
the air port caused by shifts in the wind. 
A hollow shaft having one end secured perpendicularly to the finned member 
is journalled at the other end into a housing containing three separate 
chambers. The hollow shaft communicates the air inlet port with the first 
chamber allowing fluid flow through the air inlet port into the chamber. A 
small aperture in the wall separating the first chamber from the second 
chamber damps the fluid flow from the first to the second chamber thereby 
reducing the dynamic pressure exerted by the fluid as it moves from 
chamber 1 to chamber 2. A conventional wind baffle separates the second 
chamber from the third chamber. The baffle allows the once-damped fluid in 
the second chamber to communicate with the third chamber. At the same 
time, the baffle deflects the communicating fluid in a multitude of 
directions and slows the communicating fluid to the level where the 
resulting fluid in the third chamber is substantially free of any dynamic 
pressure, and therefore truly a static fluid. The static air in the third 
chamber is then communicated to a differential pressure gauge which reads 
and compares a true static pressure outside the shack as measured from the 
third chamber of the present invention and the static pressure inside the 
shack. Pulsations and surges of outside air into the air inlet port are 
greatly reduced because the air inlet port is maintained at a constant 
angle relative to the wind direction. Furthermore, the first damping means 
between chambers 1 and 2 and the second damping means between chambers 2 
and 3 effectively eliminate any remaining pulsations or surges thereby 
producing a truly static fluid in the third chamber. Accordingly, a true 
differential pressure comparison is constantly obtained as between the air 
inside the shack and that outside the shack. 
It is therefore an object of the present invention to provide a device for 
measuring static air pressure in a moving fluid, for example air, such 
that the air inlet port is maintained at a reasonably constant angle to 
the direction of the fluid. 
Another object of the present invention is to provide additional means for 
damping a fluid such as air communicating through an air inlet port such 
that a true static pressure can be achieved for purposes of the comparison 
of the static pressure with another pressure source. 
Yet another object of the present invention is to provide an apparatus for 
measuring true static pressure in a moving fluid which is suitable for 
mounting on a building or shack such as those frequently utilized on 
offshore drilling platforms. 
A still further object of the present invention is to provide a device 
which can measure a true static pressure outside a shack situated on an 
offshore drilling platform, continuously compare the outside static 
pressure with the pressure inside the shack in such a manner that an 
accurate comparison of the two static pressures is uniformly achieved and 
wind surges and wind shifts outside the shack do not produce false high or 
low outside pressure readings which in turn cause erroneous unsafe or safe 
differential pressure readings respectively. 
These and other objects and advantages of the present invention will become 
apparent upon reading of the specification, drawings and claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 1, an elongated member 10 is exposed to a fluid stream 
(not shown), for example an air stream, and has at least one fin member 12 
secured in proximity to one end of the elongated member 10 and projecting 
radially outwardly therefrom. The fin member resultingly tends to align 
the elongated member 10 parallel to the direction of the fluid stream 
regardless of any changes in direction of the fluid stream. A weighted 
member 16, for example a sliding counterweight, can be adjustably secured 
in proximity to the other end of the elongated member 10 in order to 
further align the elongated member 10 parallel to the direction of the air 
stream while at the same time minimizing any oscillations or other 
transitory movements of the member 10. 
A hollow shaft 18, having a passageway 20 extending longitudinally 
therethrough, is secured at one end to the member 10 and is journalled at 
the other end to a housing 2 by means of a bearing housing having upper 
bearings 24 and lower bearings 26. A fluid inlet member 14, for example an 
air inlet port, is disposed on the member 10 and communicates the fluid in 
the moving stream to the passageway 20 of the hollow shaft 18. Preferably, 
the fluid inlet member is disposed on the member 10 near the axis of 
rotation of the hollow shaft 18 so as to minimize the translation of the 
fluid inlet member 14 within the fluid stream thereby minimizing dynamic 
pressure of the fluid stream within the fluid inlet member 10. 
As shown in FIG. 1, the bearing housing 22 secured to the housing 2 
rotatingly receives the hollow shaft 18 in such a manner that the hollow 
shaft 18 is substantially vertical, the elongated member 10 is 
substantially horizontal and is free to rotate 360.degree. in response to 
the direction of the fluid flow. 
The housing 2 contains therein three chambers, a first chamber 4, a second 
chamber 6 and a third chamber 8. The end of the hollow shaft 18 opposite 
the end secured to the elongated member 10 projects into and communicates 
with the interior of the first chamber 4. Consequently, the moving fluid 
at the fluid inlet member 14 can communicate with the interior of the 
first chamber 4. The first chamber 4 is partitioned from the second 
chamber 6 by means of a wall 27 which can easily be positioned in the 
housing 2 by one or more stops 30. An aperture 28 which is small in 
cross-sectional area as compared to the surface area of the wall 27 
communicates the first chamber 4 with the second chamber 6. When the 
cross-sectional area of the aperture 28 is sufficiently small in relation 
to the area of the wall 27, the aperture 28 not only communicates the 
fluid in the first chamber 4 with the second chamber 6, but also serves to 
damp the rate of fluid flow from the first chamber 4 into the second 
chamber 6. A baffle means 32, for example a conventional microphone 
acoustical baffle, separates the second chamber 6 from the third chamber 
8. The baffle means 32 both communicates the fluid in the second chamber 6 
with the third chamber 8 while at the same time multi-directionally 
deviates the flow of the fluid, thereby damping for a second time the 
fluid flow within the housing 2. The baffle means 32 can be secured to the 
housing 2 by any appropriate means, for example one or more stops 34. 
For purposes of economy, the housing 2 need not be an integral unit. A 
simple and economical way to manufacture the housing is to provide a unit 
of polyvinyl chloride pipe coupling 31 which is capped at both ends by 
insertion into a pair of polyvinyl chloride pipe caps 29. The pipe 
coupling 31 can either be threadedly or fittingly received by the pipe 
caps 29. Those skilled in the art and familiar with plastic-like materials 
will realize that plastic-like materials tend to deteriorate upon 
prolonged exposure to sunlight. The housing 2, therefore, may 
appropriately be manufactured from any suitable nonplastic-like material 
so long as the material is non-corrosive and therefore satisfactory for 
operations on offshore platforms which occur in corrosive salt air. 
Those skilled in the art will realize if the elongated member 10 has a 
chamber 11 therein which is enclosed at both ends of the member 10, the 
fluid inlet port 14 more efficiently damps the fluid flow into the 
passageway 20 than if the passageway 20 communicates with the fluid inlet 
member 14 without the presence of the enclosed chamber 11. The principle 
involved with the fluid inlet member 14 in combination with the enclosed 
chamber 11 is similar to that of the aperture 28 in combination with the 
first chamber 4 and the second chamber 6. 
Those skilled in the art will realize that the present invention as 
described and claimed herein effectively converts the moving fluid having 
both dynamic and static pressures into a fluid in the third chamber 8 
which is substantially still and, therefore, possesses only a static 
pressure. Consequently, a pressure measuring device 48 as shown in FIG. 2 
can be connected to and in communication with the static fluid within the 
third chamber 8. A suitable method for communicating the pressure gauge 48 
with the third chamber 8 is by means of a conventional hose connector 36 
as shown in FIG. 1 which receives a tube or air hose 44 as shown in FIG. 2 
which in turn communicates with the pressure measuring means or pressure 
gauge 48. 
Under operating conditions, the present invention is employed according to 
FIG. 2. A shed 38 standing on an oil platform (not shown) has an inside 
static pressure P.sub.1 and an outside pressure P.sub.2. For reasons of 
safety, it is desirable to maintain P.sub.1 at a higher level than P.sub.2 
thereby producing an overpressure inside the shed such that combustible 
hydrocarbon vapors present on the drilling platform will not enter into 
the shed 38 and be ignited. Accordingly, the ratio of P.sub.1 divided by 
P.sub.2 must continually be measured and calculated to insure that the 
overpressure inside the shed does not fall below a certain minimum 
satisfactory level. The present invention is mounted by any satisfactory 
method onto the exterior of the shed 38 as shown in FIG. 2. The static 
pressure exerted by the static air within the third chamber 8 of the 
present invention is communicated by a tube or air hose 44 to a 
differential pressure measuring gauge 48. Similarly, the static air inside 
the shed 38 is communicated by any conventional means such as an inlet 45 
in communication with an air hose 46 to the pressure differential 
measuring device 48. The pressure differential measuring device 48 is in 
turn connected to an automatic cut off switch 50 which when activated 
breaks the circuits leading to any specified number of machines and 
equipment within the shed 38. Accordingly, if the pressure inside the shed 
38 is reduced to a point wherein the ratio of P.sub.1 /P.sub.2 is less 
than the desired fraction, the cutoff switch 50 is activated thereby 
removing any necessary machinery from the line. 
It is understood that preferred embodiments of the present invention have 
been disclosed in the specification, drawings and claimed hereinafter and 
that any number of modifications, adaptations or combinations of apparatus 
are covered and included both within the scope and spirit of the present 
invention and are included within the claims appended hereto.