Valves and valve actuation – Fluid actuated or retarded – Dashpot or fluid controlled retarder or timer
Reexamination Certificate
2002-07-12
2004-08-31
Look, Edward K. (Department: 3754)
Valves and valve actuation
Fluid actuated or retarded
Dashpot or fluid controlled retarder or timer
C251S063500, C251S063600
Reexamination Certificate
active
06783107
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to equipment used in oilfield and, more particularly, to a hydraulic actuator for a valve.
BACKGROUND
Hydraulic actuators are used in the petroleum industry to open and close valves. Subsea actuators are used to operate valves for pipelines and drilling operations under water. A prior art actuator
2
is shown in schematic form in FIG.
1
A. The actuator
2
is coupled to and adapted to control a valve
8
for a pipeline
9
. The actuator
2
is coupled to a control system
6
which may comprise a hydraulic three-way valve, for example. The actuator
2
, control system
6
and hydraulic lines coupled therebetween are submerged in seawater. A hydrostatic head
7
comprises pressure generated due to the height of the fluid column at a given depth under the water surface
5
. For example, the hydrostatic head
7
generated by seawater at 10,000 feet depth is 0.433 p.s.i./foot×10,000 feet=4,333 p.s.i. The amount of pressure generated is dependent on the type of fluid in the column. For example, hydraulic fluid generates less pressure than seawater. Hydraulic fluid may be pumped into the control system
6
through a hydraulic control line coupled from the water surface
5
to the control system
6
at an input port I.
The actuator
2
includes a spring
4
adapted to exert pressure on a piston
3
. The piston
3
may be sealed with o-rings inside the actuator housing. The control system
6
is coupled to the actuator
2
at port P
1
in a region above the piston
3
, and also is coupled to the actuator
2
at port P
2
in a region below the piston
3
, for example, with hydraulic lines. Hydraulic fluid may be sent from the control system
6
to actuator port P
1
to move the piston
3
down. Similarly, hydraulic fluid may be sent from the control system to actuator port P
2
to move the piston
3
up.
The control system
6
also includes a vent V into the sea where excess hydraulic fluid may be leaked out. For example, when the piston
3
goes up, the control system
6
dumps a corresponding volume of hydraulic fluid into the sea through the vent V. When in a vent mode, the control system
6
communicates with the seawater, and the hydraulic fluid within the control system
6
may become contaminated with seawater. Seawater, which contains corrosive chemicals such as chlorides, for example, can enter the spring chamber
12
of the actuator
2
and corrode the spring
4
and other parts of the actuator
2
. If the spring
4
corrodes, this can cause failure of the actuator
2
. Because the spring
4
is typically the most mechanically stressed component in the actuator
2
, corrosion of the spring
4
may cause the spring
4
to fracture into a number of pieces. Failure of the spring
4
usually renders the actuator
2
inoperable for controlling a gate valve
8
.
Furthermore, a hydraulic line from the control system must be provided into port P
2
to supply a hydrostatic head underneath the piston
3
in order to achieve equilibrium. Each actuator
2
in use under the sea requires one hydraulic line from the control panel
6
. In subsea applications, there are a limited number of hydraulic lines available for use.
As described above, prior art actuators
2
are not designed to accept seawater inside, which can corrode various components such as the spring
4
. In an attempt to prevent seawater from entering hydraulic actuators, an external pressure compensator
10
can be coupled between the control system
6
and port P
2
of the actuator
2
, as shown in FIG.
1
B. The external pressure compensator
10
, also referred to herein as a piston accumulator or piston accumulator system, is a separate component from the actuator
2
and provides hydrostatic pressure compensation of hydraulic fluid displaced within the actuator
2
during operation. The pressure compensator
10
prevents seawater-contaminated hydraulic fluid from the control system
6
from entering port P
2
in the actuator spring chamber
12
, thus preventing corrosion of the spring
4
.
However, external pressure compensators
10
are typically attached to the actuator
2
by brackets (not shown), for example, and are fluidly coupled to the actuator
2
by piping at P
2
. The connection joints of the piping provide potential leak sites, which may affect the reliability of the actuator system. Thus, a need exists for an actuator and compensator package that has fewer potential leak sites, to improve the reliability of the system.
Furthermore, using an external pressure compensator
10
is disadvantageous in that an additional component and installation is required, requiring increased cost and labor. Reliance on an additional manufacturer (e.g. for the pressure compensator
10
) is required, and more engineering is required, to select the size, pressure rating and availability of the external compensator. Clamping and mounting the compensator
10
with the actuator
2
can be problematic, requiring more connections and leading to more leakage paths, so that a chance of seawater entering the spring chamber
12
is created.
The use of an external pressure compensator
10
also increases the space required. There may be space restrictions at the installation site for the actuator
2
that may make it difficult or unfeasible to use an actuator
2
with an external pressure compensator
10
.
SUMMARY OF THE INVENTION
Embodiments of the present invention achieve technical advantages as a hydraulic actuator with a built-in pressure compensator. Hydraulic fluid that is possibly contaminated with seawater is prevented from entering the chamber containing the spring, preventing corrosion of the spring and extending the usable life of the actuator.
In accordance with one aspect of the present invention, a hydraulic actuator includes an actuator housing, a built-in pressure compensator, a first housing internal chamber, and a first hydraulic via. The built-in pressure compensator is located within the housing. The built-in pressure compensator includes a compensator cylinder portion, a compensator piston portion, a first compensator piston chamber, a second compensator piston chamber, and a compensator hydraulic port. The compensator cylinder portion is located within the actuator housing. The compensator cylinder portion is fixed relative to the housing and has an internal chamber formed therein. The compensator piston portion slidably fits within the compensator internal chamber.
The first compensator piston chamber is formed between a first side of the compensator piston portion and the compensator cylinder portion within the compensator internal chamber. The second compensator piston chamber is formed between a second side of the compensator piston portion and the compensator cylinder portion within the compensator internal chamber. The compensator hydraulic port is routed through the housing, with one end opening outside of the housing and the other end opening to the first compensator piston chamber. The first housing internal chamber is formed within the housing. The first hydraulic via is formed through the compensator cylinder portion, fluidly coupling the second compensator piston chamber with the first housing internal chamber.
In accordance with another aspect of the present invention, a hydraulic actuator is provided, which includes a housing, an operating stem, a first cylinder portion, a first housing internal chamber, a second housing internal chamber, a spring, a first piston portion, a first piston chamber, a second cylinder portion, a second piston portion, a second piston chamber, a third piston chamber, a first hydraulic port, a second hydraulic port, a first hydraulic via, and a second hydraulic via. The operating stem extends into the housing and is slidably coupled to the housing. The first cylinder portion slidably fits within the housing and has a first cylinder internal chamber formed therein with a closed end and an open end. The first cylinder portion is mechanically coupled to the operating stem. The first housing internal chamber is
Fristoe Jr. John K.
HP&T Products, Inc.
Look Edward K.
Slater & Matsil L.L.P.
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