Fluid handling – Systems – Flow path with serial valves and/or closures
Reexamination Certificate
2001-05-31
2003-08-19
Rivell, John (Department: 3753)
Fluid handling
Systems
Flow path with serial valves and/or closures
C137S601200, C137S590000, C137S493900, C251S083000, C251S121000, C251S274000
Reexamination Certificate
active
06607007
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to valves for controlling the flow of fluids, particularly gases, and more specifically to valves for more safely regulating the flow of oxygen gas.
2. Background Art
Oxygen is widely used in many medical and industrial applications. When a portable source of oxygen is required, it is almost universally supplied in the form of molecular oxygen (O
2
) under pressure in a cylindrical steel or aluminum container. Oxygen commonly also is transported in such cylinders. The cylinders are equipped with a valve, used to open and close the cylinder for emptying and refilling. A pressure regulator often also is attached to the cylinder valve.
Oxygen cylinder valves, as they exist today, have been implicated in numerous fire incidents with sometimes catastrophic results. When a cylinder valve seat ignites, the attached regulator or manifold system is subjected to strong kindling chain mechanisms that will often lead to fires downstream of the cylinder valve.
The “plug type” cylinder valves presently in common use comprise a rotating threaded seat plug that translates due to the rotation of a hand wheel mounted on the top of the valve itself. The plug incorporates a relatively large nonmetallic seat. The seat is subjected to strong flow impingement during oxygen gas discharge from the cylinder, due to the seat's orientation above the valve nozzle. Further, due to the rotating seat mechanism, the seat often is subjected to strong frictional interference with the valve nozzle. Both of these features are undesirable to prudent persons aware of the fire hazards of handling oxygen cylinders. Conventional known valves are also “dirty,” generating large amounts of undesirable debris due valve). This debris often deposits in the nonmetallic seat itself and increases the frictional interactions during valve opening and closing.
These valves most often utilize a nylon main seat although both polyphenylene oxide (PPO) and polychlorotrifluoroethylene (PCTFE) are also utilized. Both Nylon and PPO exhibit poor to moderate compatibility based on present oxygen-compatibility rating test standards, and deliver a large amount of energy if ignited. PCTFE is considered an oxygen compatible material, but has a compressive modulus that is insufficient to withstand the torques that are often applied by the manual closing of valves. As a result, PCTFE seated plug-valves often exhibit significant extrusion and recently have been implicated in a large number of fires. The extruded seat increases the surface-area-to-volume ratio for oxygen gas impingement during discharge, and is believed to greatly increase vulnerability of the seat to hazardous flow friction ignition.
FIG. 1
depicts the generalities of known container-and- valve construction, shown in partial cross-section to reveal the function of interior elements. These types of containers are in common use by the millions around the world, to contain oxygen and other gasses under pressure for use. A known valve assembly, shown at
10
, has a plug portion
11
threaded so to be securely screwed into the correspondingly threaded opening
12
at the “top” end of a conventional pressurized gas cylinder
15
or tank. In this specification and in the claims, “top” and “bottom” and “up” and “down” refer to a valve assembly and cylinder as oriented in
FIG. 1
, that is, with the axis of the cylindric container perpendicular to the ground, the valve sitting atop the cylinder and the planar bottom resting upon the ground. (This is the position in which conventional cylinder tanks are commonly stored and transported, although they are used in practically any position.) However, it must be clear that the present invention may be used with the container or tank in any position with respect to vertical or to the ground, including an inverted position in which the container is above the valve while in use.
In conventional gas container valves, sometimes called Sherwood valves, the handle
17
connects to a stem
21
which is retained inside the main body
20
by a cap or jam nut. The stem
21
engages a threaded plug
23
that has a screwed engagement with the body
20
of the valve
10
. A valve seat
24
, typically fashioned from nylon or a flexible plastic, is retained within the distal end of the plug
23
. The main body
20
has a radial port
25
through which gas can enter and exit an upper chamber
27
defined in valve body
20
. The body also has a lower or first chamber
28
, located about the valve's axis and via which gas may flow to and from the interior
13
of the container
15
. The valve has an imaginary, central, longitudinal axis, generally describing the axis of symmetry of the body
20
, and along which the handle
17
and stem
21
translate during operation. The body
20
defines an interior annular nozzle
30
, a constriction dividing the lower chamber
28
from the upper, second chamber
27
. The lower or first chamber
28
is in fluid connection with the second or upper chamber
27
, as there is an orifice at the center of the nozzle
30
through which gas may flow. Rotation, e.g. manual rotation, of the handle
17
also rotates the stem
21
at the same rate, since the stem is connected to the handle. The plug
23
both rotates and translates in its threaded disposition within the body
20
. Rotation of the handle and stem
21
thus cause the plug
23
to move axially, e.g. up and down, within the body
20
. The seat
24
is contactable against the upper side of the nozzle
30
to close the nozzle orifice. Thus, the rotation of the handle
17
and stem
21
in the stem-engaging portion
19
shifts the plug
23
and seat
24
into and out of contact with the upper side of the nozzle to close and open the nozzle, and thus the valve
10
, to the passage of gas. A helical spring
33
typically (but not necessarily) is employed to aid sealing of the stem packing seal. Standard clockwise rotation of the handle (as indicated by the directional arrow in
FIG. 1
) screws the plug
23
downward, and presses the seat
24
against the nozzle
30
to close the valve.
The foregoing commonly encountered valve design suffers from several functional drawbacks, especially when oxygen is the gas of interest. Most of the serious deleterious effects occur when a tank
15
containing oxygen under pressure is opened to discharge the oxygen for use. This discharging step is the most common circumstance of hazardous fire. Continued reference is made to FIG.
1
. When the handle
17
is rotated counterclockwise to separate the seat
24
from the nozzle
30
to release oxygen under pressure from the interior
13
of the container
15
, the high-velocity oxygen stream flows through the first conduit or chamber
28
and is further accelerated by passage through the orifice of the nozzle
30
en route to escape through the second port
25
. Ordinarily, this high-velocity oxygen stream impacts directly upon the valve seat
24
immediately after passing through the nozzle
30
. Fast-moving oxygen molecules impinging against a seat
24
commonly fashioned from nylon or plastic is a condition which fosters dangerous combustion of the seat. The combustion can then be spread downstream by the gas exiting the valve
10
.
Also, it is noted that in known devices the separation of the seat
24
from the nozzle
30
occurs rapidly, i.e., just a partial rotation of the handle
17
and stem
21
may be adequate to disengage entirely the seat from the nozzle. Stated differently, the rotation of the stem
21
in the body
20
moves the seat rapidly upward, so that the axial distance of separation between the seat and the nozzle increases rapidly, resulting in a very quick change from a “fully closed” to “mostly open” flow condition. This rapid opening of the valve results in near adiabatic pressure changes which may heat valve components downstream, including the attached regulator. It also promotes deleterious mechanical friction and gas flow friction past the seat
24
.
Further
Hull Wendell C.
Newton Barry E.
Baker Rod D.
Peacock Myers & Adams P.C.
Rivell John
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