Abstract: A subsea electric actuator comprises an electric motor and a telescopic drive connection (8) from the motor to a drive unit (10, 11, 12) which can be moved to and fro and converts rotary motion of the connection to linear motion of an actuating stem (5). A return spring (14) is operable on the drive unit to urge the actuating stem towards a datum state. An electromagnetic latch (15) is operative when set to maintain the drive unit in a predetermined position so as to decouple the action of the return spring whereby the stem can be advanced and retracted relative to the drive unit free from the action of the return spring. De-energization of the latch allows the return spring to operate on the drive unit to return the actuating stem to the datum state. Various forms of electromagnetic latch are described.

Abstract: A subsea wellhead assembly includes a production casing hanger defining a series of passageways from an annulus between a production casing string and an outer casing to a region that can communicate, for example, by way of an isolation sleeve, with a production tree. The passageways extend to the interior of the casing hanger. A positionally adjustable sleeve fits within the casing hanger and carries exterior seals that are disposed so that for a first position of the adjustable sleeve within the casing hanger, fluid passage through the series of passageways is blocked, and for a second position of the sleeve within the casing hanger, the fluid passage is allowed. The adjustable sleeve can be operated by a simple tool through the production tree.

Abstract: A hydraulic valve comprises a plurality of ports, which communicate with a passageway, and a valve member movable in the passageway to control the communication between the ports. The valve member carries a lateral shear seal which is integral with the valve member and engages the passageway. In one position, the valve member isolates a first port from a second port. In another position of the valve member, the shear seal communicates with the first port and provides communication between the first port and the second port by way of a passage within the valve member. The valve member has first and second portions of different effective cross-section areas and on each portion an integral sealing member makes a radial seal between the valve member and the passageway. A supply port supplies pressure to the outside of the valve member so as to produce by virtue of the different cross-sectional areas a force tending to move the valve member towards a closed position.

Abstract: A subsea wellhead assembly includes a wellhead body which disposed to support an isolation sleeve for a production tree and to support below the isolation sleeve a production casing hanger for a production casing string. The body also supports a second casing string outside the production casing string whereby to form an annulus between the casing strings. The body includes a passageway which is in communication with the annulus near a lower end of the body and extends upwardly within the wall of the body towards the upper end of the body. A valve is accommodated in the upper part of the body and provides controlled communication between the passageway and a port which can be coupled to the isolation sleeve. The valve is controllable from a production tree in particular is moveable between an open position and a closed position in response to fluid pressure applied to the valve from a production tree by way of the isolation sleeve.

Abstract: Apparatus for the insertion of a pack-off into a recess in a bore of a wellhead body includes an activating sleeve which has a portion disposed for engagement with the pack-off for the movement of the pack-off into the recess and body portions shaped for location on a datum member within the bore. The activating sleeve includes a plurality of apertures circumferentially spaced about the activating sleeve. A running tool which is adapted to move the activating sleeve into engagement with the pack-off carries spring-loaded dogs each disposed in one of the apertures. Each of a plurality of releasing pins is positioned such that it enters a respective one of the apertures when the activating sleeve has caused the pack-off to be located in the recess. The entry of the pins into the apertures causes depression of the dogs out of the apertures and allows the consequent release of the activating sleeve from the running tool.

Abstract: A subsea valve comprises a valve gate (4) moveable within a valve cavity (3) and a main passageway (2) extends transversely of the cavity. At least one annular valve seat (6) is in communication with a respective portion of the main passageway and extends to engage the gate. An annular pocket (7, 7a) accommodates an end of the respective seat remote from the valve gate. The seat has at the said end an annular buffer (54) in radial engagement with the pocket (7) and comprising a multiplicity of cantilever springs (55) each extending radially and circumferentially of the rim of the seat.

Abstract: A method of transmitting on a transmission line a set of carrier signals of which at least one component represents a respective data value and the carrier signals are of different frequencies ranging from a lowest frequency to a highest frequency, in which the respective component of each carrier above the lowest frequency is adjusted on transmission in accordance with a selected relationship between that respective component and the corresponding component of the next lower frequency so as to compensate for the frequency-dependent effect of the transmission line on those components. The components may be amplitudes. The relationship may be a ratio of the respective and corresponding components.

Abstract: A subsea wellhead a generally cylindrical body including a lower extension for forming an annular space for a cement column between the lower extension and an outer conductor. The extension carries a multiplicity of interfitting rings forming a sleeve which facilitates flexure of the extension in the presence of the cement column. Each ring may comprise an inner flange for disposition adjacent the outside of the extension and an outer flange for fitment over the inner flange of an adjacent ring. The outer flange may have a radial through-bore.

Abstract: A modem for use with a subsea transmission line comprises a digital signal processor responsive to a succession of segments of a data signal to produce a respective set of orthogonal frequency division multiplexed signals and to transmit those signals as a burst on the transmission line, and to prepend the burst with a start signal comprising a cyclically time-varying signal envelope-modulated with a Gaussian waveform. The modem is also arranged to convert signals received from the transmission line into a succession of digital samples and to process those samples to obtain an indication of the peak of the Gaussian waveform whereby to provide a datum for decoding a received burst of OFDM signals.

Abstract: An actuator with a predetermined failure mode includes two carriers which are each moveable in a common direction. A detent is engageable to couple the carriers to move in unison. An electrically operated actuating device causes extension of the toggle linkage to operate the detent and collapse of the toggle linkage when de-energized. There is a prime mover for the first carrier and a return mover for causing return movement of the second carrier on the release of the detent. In an example, the detent includes a pivoted arm disposed on the first carrier and positioned to engage a part of the second carrier; and the toggle linkage includes a pair of relatively pivoted links connected between a pivot on the first carrier and a pivot on the arm.

Abstract: A control valve includes a body including an internal passageway and is constituted at one end as a coupler that includes a valve poppet openable to allow fluid access to or from the passageway past the poppet. The body defines at least one lateral port. A valve spool is disposed within the body and is movable lengthwise of the body by a solenoid actuator, disposed at the other end of the body, to control fluid communication between the passageway and the lateral port.

Abstract: A subsea stab plate assembly includes a stab plate which has apertures each extending in an axial direction through the plate from a front face of the plate to a rear face of the plate. A subsea hydraulic coupler has a body with an internal longitudinal passageway including a valve operable to open the passageway on the mating of the coupler with a complementary coupler. The coupler is shaped for insertion through an aperture in either of two directions, having a circumferential groove and a flange assembly including an axially extending hub which fits into the groove and a shoulder for abutment against the front face of the plate. The flange assembly includes a plurality of separable segments, each of which constitutes part of the hub and part of the shoulder. The hub fits between the groove and the inside of the aperture.

Abstract: In a token bus system a node with the token can transmit on the bus a packet that contains two destination addresses. One address specifies the node that should receive the data component (payload) of the transmitted packet. The other address specifies the node that should receive the token. The network protocol specifies that a node with the token must immediately transmit a packet containing just the token or a packet with token and data if it has data to send. When no data is being passed from one node to another on the network, the token may be passed from one node to the next in order. Each node will pass the token to the next highest node number. If a node has the token has some data for sending it transmits a packet with the token for the next node and data for any of the nodes. The bus system requires every node to receive all packets and process them to determine whether the token or the data (or both) is destined for that node.

Abstract: An electrically operated hydraulic valve comprises a valve assembly that provides a common valve passageway, an inlet port, an outlet port and a return port connected to the passageway and an axially movable valve device which allows in a first position fluid flow between the outlet port and the return port while closing the inlet and in a second position, axially displaced from the first position, fluid flow between the inlet port and the outlet port while closing the return port. A spring provides a restoring force urging the valve device to its first position. An electrically operated actuator coupled to the valve device comprises a permanent magnet and a cooperating electrical coil having an associated magnetic core, one or other of the magnet and the coil constituting a stator and the other constituting an armature which is coupled to the valve device to move it from the first position to the second position.

Abstract: A subsea female coupler has a body defining a socket for the reception of a probe of a male coupler. The socket includes an annular shoulder and, outwardly of the shoulder, a part-conical seat which tapers towards the interior of the socket. An annular seal is disposed to provide radial sealing between the socket and the probe and is positioned in the annular shoulder. A metal retainer in the form of a securing ring, which has a bevelled rim for abutment with the seat, provides sealing between the region of the seal and the exterior of the body of the coupler. The retainer has a screw-threaded periphery for engagement with a complementary thread on the interior of the socket. An inner ring liner fits within the retainer and has a flange for abutting the seal.

Abstract: A cap for a subsea tree having a re-entry hub (1) and for use with a tubing hanger (25) deployed within the tree comprises an outer sleeve (3) for fitment over the hub and an inner sleeve (19) adapted to extend within the hub. The sleeve has communication couplers (27, 37) for cooperation with the tubing hanger. Preferably the communication couplers are located at the extremity of the inner sleeve. The couplers can accommodate dummy plugs or live couplers to suit the mode of application. The inner sleeve (19) supports at least one annular seal (21, 22) which provides a barrier between the inner sleeve and the inner periphery of the hub. The outer sleeve (19) includes releasable engagement fittings (16) for securing the outer sleeve to the hub. The cap is adapted for use as a running tool.