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The most
common requirement for key interlocking
of poweractuated valves occurs in Pig Launcher/
Receiver systems, Scraper Traps and Sand
Filter systems etc. where poweractuated
valves need to be interlocked with manually-operated
valves and the vessel closure.
Because of the ultra-critical nature of
such valves, special considerations arise
which the design of a key interlock system
must address:-
Where such valves are part of an ESD system, the key interlock system must not compromise the valve's fail-safe function.
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Where pigging operations occur, the key interlock system must verify the valve's absolute position (Open and/or Closed) independent of any on-board instrument indication.
On electrical actuators where the key interlock system de-energises the valve, any anti-condensation heating circuitry etc. must remain uninterrupted.
Where actuators are equipped with a manual override facility, the key interlock system must permit operation of the valve in both modes (or in a combination of both modes - e.g. in the event of a power failure) while maintaining the integrity of the key sequence at all times. |
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Because actuators generate great torque forces,
(b)locking of such valves by mechanical restraint
is unacceptable - such locking methods would likely induce
damage within the motor assembly.
Nonetheless, a key interlock system must ensure the valve is de-energised and disabled (in both Remote and Local modes) and that only the appropriate sequence key is released for continuation
of the procedure dependent on the valve's verified
(Open or Closed) position.
A typical operating sequence is given on the page opposite
where it may be observed the interlock system functions
‘passively’ and relies on the as-built actuator
mechanisms to establish and confirm the status of the
equipment.
It may also be observed when such valves are in the ‘Open’
(‘Remote’ setting)
position - the valve is free to operate to ‘Closed’ without hindrance or interruption by the interlock system. |
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'SLU' Switch Unit Locked in 'REMOTE'.
'HWL' Handwheel Drive Locked 'OFF'.
'A' Key in Control Room.
To Close Valve:
1. 'A' Key into 'AKE' positional indicator unit.
'B' Key is removed from 'AKE' - 'A' Key trapped.
2. 'B' Key into 'SLU' Switch Unit to unlock.
'SLU' Unit switched to 'LOCAL' ('B' & 'C' Keys trapped).
Operate button to close valve.
3. 'SLU' Unit now switched to 'OFF' - 'C' Key is removed.
'SLU' Unit locked in 'OFF' position trapping 'B' Key.
4. 'C' Key into' AKE' Unit - remove 'D' Key trapping 'C' Key. 'D' Key is then directed towards continuation of the procedure.
NB The 'D' Key will not release unless the valve has completed its full stroke to the CLOSED position. |
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'SLU' Switch Unit Locked 'OFF'.
'ATL' Handwheel Drive Locked 'OFF'.
'D' Key in Control Room.
To Open Valve:
1. 'D' Key into 'AKE' positional indicator unit.
'C' Key is removed from 'AKE' - 'D' Key trapped.
2. 'C' Key into 'SLU' Switch Unit to unlock.
'SLU' Unit switched to 'LOCAL'('B' & 'C' Keys trapped).
Operate button to open valve.
3. 'SLU' Unit now switched to 'REMOTE' - 'B' Key is removed. 'SLU' Unit locked in 'REMOTE' position trapping 'C' Key.
4. 'B' Key into 'AKE' Unit - remove 'A' Key trapping 'B' Key.
'A' Key is then directed towards continuation of the procedure. NB The 'A' Key will not release unless the valve has completed its full stroke to the OPEN position. |
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A range of comparable designs are also available for sprungreturn and non-return hydraulic actuators and for sprung-return pneumatic actuators.
SFC's range of special process products also includes needle valve locks, temperature and pressure sensing locks and a range of signalling options to meet most process operating requirements. |
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In the event of a power failure at anytime during either of the above procedures, it is essential the integrity of the key sequence is maintained if the valve is operated manually. This is achieved simply by locking the 'SLU' Unit in the 'OFF' position thereby releasing the 'C' Key. (Even if power is restored,
with the 'C' Key free, the valve/actuator will remain disabled).
The 'C' Key is inserted into the freewheeling 'ATL' handwheel assembly - this lock functions on a 'declutching' principle. With the 'C' Key trapped, the 'ATL' drive mechanism may be engaged thereby enabling the valve to be operated.
While the 'C' Key can be removed from the 'ATL' assembly at any time, it has to be exchanged through the 'AKE' unit to secure the continuation key (i.e. the 'A' or '0' Keys in the above examples)- these keys will only release provided the valve has completed its full stroke. |
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The range of process applications to which SFC interlocks can be applied is unlimited. As clients begin to understand the immense operational capabilities of SFC interlock systems, they often request unique solutions to specific problems.
In this section we present some examples of
'specials' we have developed to meet clients'
specific operating safety requirements.
SFC are always pleased to receive a challenge to provide unique solutions to clients' individual or special problems. |
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| To ensure two ports on an instrument manifold can never be simultaneously opened. |
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Needle valves of all types can be fitted with SFC interlocks. Regardless of body design, number of operating handles or method of operation, SFC can supply a solution to your problem. In this illustration a 4-port instrument manifold is equipped with SFC's NVL interlock. The locking device ensures that pairs of operating handles can only be operated one at a time. Upon opening the first port, the key becomes trapped. The second port cannot be opened until such time that the first port has been closed, thus releasing the operating key.
The opposite pair of ports are controlled in the same way with a differently coded key. |
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Download here :
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You can download an animation showing a typical actuator system by clicking on the icon |
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You can download a PDF version of the datasheet by clicking on the icon |
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