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Detailed description of four ram gear hydraulic system

Ships from at least the 1950s, have been fitted with automatic steering, making helmsmen redundant for deep sea passages. After the required course is set, the automatic steering maintains direction; correcting any deviations due to the weather.

Four ram gear hydraulic steering system

The drawing of a four ram gear (Figure 9.14) shows the Rapson slides, the combined guide and brace arrangement previously described and the control box with its connecting link from the rudder stock. A second link from the stock to the rudder angle indicator transmitter, is also shown.

The hydraulic circuit (Figure 9.15) incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. Inactive cylinders are isolated from the pumps by valves while the bypass valves connecting them, are opened to permit free flow of idle fluid. Either or both duplicate independent power units may be employed with any usable combination of cylinders.

It will be seen that the torque available from two cylinders is only one-half of that from four, even when both power units are working, though the speed of operation will be increased if both are used. The mechanical arrangement of the control gear and the basic hydraulic system, in all but their layout (Figure 9.15) are identical with the two ram gear already described.

Four-ram electro-hydraulic steering gear with electric control
Figure 9.14 Four-ram electro-hydraulic steering gear with electric control(Brown Bros & Co Ltd)

Hydraulic circuit for four-ram electro-hydraulic steering gear
Figure 9.15 Hydraulic circuit for four-ram electro-hydraulic steering gear(Brown Bros & Co Ltd)

B1-B4. (By-pass valves) ,C1-C4. (Cylinder isolating valves)

Hydraulic circuit for four-ram electro-hydraulic steering gear
fig: 9.11 Hydraulic circuit details for four-ram electro-hydraulic steering gear(Brown Bros & Co Ltd)

The valve chest however, must cater for four cylinders in all useful combinations. This demands four cylinder isolating valves, C1-C4, and four bypass valves, BlóB4. The emergency hand pump arrangement, its directional control valve, the main system relief and the locking valves remain unchanged, as do the remote, local and emergency control arrangements.

Normally, the pump and the four cylinder isolating valves, Pi, P2, C1-C4, and the rudder locking valves LV, are open. The bypass valves BlóB4 and the emergency hand pump isolating valves HP are closed. Power units may be brought into action or shut down, by starting or stopping the associated motors. To change from four ram to two ram working, it is only necessary to make two cylinders inoperative by closing their isolating valves C1-C4 and opening the bypass valves between them.

For example to steer on cylinders 1 and 3, valves C2 and C4 are closed; B2 and B4 are opened so that cylinders numbers 2 and 4 are isolated from the main hydraulic system and the oil in them is free to flow from one to the other. The cylinder isolating valves and the bypass valves are shown as separate items in diagram but each pair may be combined as a double seating valve so that, as any cylinder is isolated from the main hydraulic system it is automatically opened to a bypass manifold and to the other inoperative cylinder.





Summarized below various ship steering gears general guideline:
  1. Ship Steering gear failures and safeguards

  2. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  3. Four-ram electro-hydraulic steering gear mechanism

  4. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  5. Enclosed hunting gear

  6. The light construction of the combined control and hunting gears is possible because the forces concerned are moderate. The self-contained unit is self-lubricating, and contained in an oil-tight case. ......

  7. Ship steering control mechanism- use of Hydraulic telemotor

  8. The telemotor has become, on many vessels, the stand-by steering control mechanism, used only when the electric or automatic steering fails. It comprises a transmitter on the bridge and a receiver connected to the steering gear variable delivery pump, through the hunting gear. ......

  9. Two-ram electro-hydraulic steering gear with variable delivery pumps

  10. An arrangement of a two-ram steering gear with variable delivery pumps may have a torque capacity of 120-650 kNm. The cylinders for this gear are of cast steel but the rarns comprise a one-piece steel forging with integral pins to transmit the movement through cod pieces which slide in the jaws of a forked tiller end. ......

  11. Rudder carrier bearing & Steering gear

  12. The rudder carrier bearing takes the weight of the rudder on a grease lubricated thrust face. The rudder stock is located by the journal beneath, also grease lubricated ......

  13. Small hand and power gears - Ship steering systems

  14. A simpler variant of the electro-hydraulic gear, for small ships requiring rudder torques below say, 150 kNm ......

  15. Four ram gear with servo-controlled axial cylinder pumps

  16. Variants of the servo-controlled swash plate axial cylinder pump are capable of working at 210 bar. Each pump is complete with its own torque motor, servo-valve, cut-off mechanism, shut-off valve and oil cooler. ......

  17. Vane type gear - provides security of four ram steering gear

  18. These may be regarded as equivalent to a two-ram gear, with torque capacities depending on size. An assembly of two rotary vane gears, one above the other, provides the security of a four ram gear. ......

  19. Details of two ram hydraulic steering gear arrangement

  20. When the main pumps are at no-stroke, the auxiliary pumps dischar. to the reservoir via a pressure-limiting valve PC20, set at 20 bar, and to t pump casings. When the main pumps are on-stroke, the auxiliary pump discharge to the main pump suction. ......



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