An engagement device

An engagement device (50) connected to the lower face of a christmas tree for engaging/disengaging a stabbing pin (52) connected to a wellhead release mechanism comprises a movement mechanism (56) and an engagement arrangement (54). A piston (2), ram shaft (4) and balance rod (5) are connected together with the piston (2) being moveable within a hydraulic fluid chamber (8). The balance rod (5) has a larger external diameter than the ram shaft (4), thus the lower face of piston (2) presents a larger cross-sectional area to the hydraulic fluid in the chamber (8) than the upper face. This leads to a greater force being exerted on the lower face (i.e. the pulling direction). To disconnect a christmas tree from the subsea wellhead, four engagement devices (50) synchronously engage and then pull each stabbing pin. Hydraulic fluid introduced into chamber (8) through adaptor (22a) forces the engagement arrangement towards the stabbing pins. Hydraulic fluid in a second chamber (48) urges a collet piston (28) downwards (to the left as shown). This causes collets (36) to engage the stabbing pins. Introducing fluid at a high pressure into chamber (8) through adaptor (22b) causes piston (2) and the rest of the engagement arrangement including the collet housing (26) to move upwards resulting in the stabbing pins being pulled out of engagement with a spring locking mechanism (not shown).