Pig signaller is a device installed on a pipeline or pig trap assembly to detect movement of pig. It consists of a mechanism which detects the movement of pig.
There are two types of pig signallers depending on the detecting mechanism:
The intrusive type are mechanically operated and are generally bi-directional. They have mechanically operated
signal flags which can be reset and are suitable for mounting on both vertical and horizontal pipelines. The
indicating device, 'Flag', is normally set in the horizontal position for "pig not passed" and vertical for
"pig passed" condition with a manual latch reset to the horizontal position.
It is important to install the trigger in the correct orientation. The axis about which the trigger rotates should be perpendicular to the pipeline axis. In pipelines where uninterrupted operation is critical, pig signaller with an integral ball valve is used. The ball valve together with a retriver kit facilitates removal of the trigger mechanism while the pipeline is still operating.
Pig signallers from manufacturers such as GD Engineering are designed for installation through a minimum bore of 39mm. The pig detector base should be compatible with the pipeline material to which it will be welded. For pig signallers used in sour service the elastomeric materials for ring seals shall resist explosive decompression and shall be suitable for the long-term exposure to the transported fluid at the design pressure and temperature conditions.
While ordering pig signallers the thickness of the pipeline should be provided to the Vendor. Though the trigger mechanism can extended or retracted within the pipeline the amount of adjustment is limited to about 25mm.
For buried pipelines, the pig signaller must be procured with an extended body. Pig signallers upto extensions of 2.2m are commercially available.