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The pilot valves in the subsea pods are controlled from the surfacenn

Pilot Fluid Circuit (2-Position Function)

The pilot valves in the subsea pods are controlled from the surface by means of control valves located in the hydraulic control manifold. These control valves can be operated either manually from the control manifold itself or remotely from an electrical panel via pneumatic solenoid valves.

Any BOP stack function such as a failsafe valve, which requires pressure only to open or close it is called a 2-postion function. There is an u2018operateu2019 position and a u2018ventu2019 position. The latter position is used to release pressure from the operating side of the pilot valve.

The schematic aboveu00a0shows a typical 2-position function pilot circuit. The control valve, a u00bcu2019, four-way manipulator valve, can be controlled from a remote panel via the two solenoid valves which can place the valve either in the u2018openu2019 or u2018ventu2019 positions. A pressure switch connected to the discharge line of the control valve is activated when a pilot signal is present and lights up the appropriate lamp on the control panel.

In the u2018openu2019 position the pilot signal is transmitted to the subsea control pods where it operates its associated pilot valve which then allows the power fluid to flow through the selected pod to the BOP function.

A BOP stack function requiring pressure to both open and close is called a 3-position function. The hydraulic pilot fluid circuit for a 3-position function is shown below. It requires the use of three solenoid valves, the u2018blocku2019 solenoid valve being used in conjunction with two shuttle valves in order to centre the control valve.

Pilot Fluid Circuit (3-Position Function)

A pressure switch is connected to each discharge line of the control valve and will transmit a signal to the appropriate control panel lamp whenever a pilot circuit is as described above.

The main components of the control system and some of the other operating sequences areu00a0 described in more detail in the next lesson.