Hydraulic power rotary pumps

Rotary positive displacement pump

o A positive displacement pump has an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Liquid is allowed to flow into the pump as the cavity on the suction side expands and the liquid is forced out of the discharge as the cavity collapses.oPositive displacement rotary pumps move fluid using

a rotating mechanism that creates a vacuum that captures and draws in the liquid.

Advantage

• Rotary pumps are very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually.

Drawbacks• The nature of the pump

demands very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed.

• If rotary pumps are operated at high speeds, the fluids cause erosion, which eventually causes enlarged clearances that liquid can pass through, which reduces efficiency.

Radial cylinder pump AKA Hele-Shaw Pump

PartslCentral ValvelCylinder BodylPistonslRotor and Floating Ring

Central Valve

The central valve is a round bar which serves as a stationary shaftaround which the cylinder body rotates.

Two holes serve as the intake and the other two as thedischarge. Two slots are cut in the side of the shaft so that each slot connects two of the lengthwise holes. One of these slots provides the path for the liquid to pass from the cylinders to the discharge hole bores into the central valve. The other slot connectsthe two inlet holes to the cylinders during the entrance of liquid.

Cylinder Body

The cylinder body in the figure has a hole bored through the center toaccommodate the pintle. Both the cylinder holes and the center hole arevery accurately machined so that liquid loss around the pistons and the central valve is kept to a minimum.

Pistons

Like cylinder bodies, pistons are made in different designs. Like the cylinder walls, the sides of the pistons are accurately machined to fit thecylinders, so there is a minimum loss of liquid between the walls of thecylinders and the pistons. No provision is made for the use of piston rings to help seal against leakage.

Rotor and Foating Ring

The rotor consists essentially of a circular ring, machine finished on the inside, against which the pistons bear. The rotor rotates within the floatingring which can be shifted from side to side to control the length of the stroke of the pistons. The floating ring has two pairs of machined surfaces on the exterior so that it can slide in tracks in the pump case.

Swash Plate type

Has a circular cylinder block with axial cylinders deposed on a pitch circle around a central bore.Also have a rotating cylinder containing pistons. A spring pushes the pistons against a stationary swash plate, which sits at an angle to the cylinder. The pistons suck in fluid during half a revolutionand push fluid out during the other half. It contains two semi-circular ports. These ports allow the pistons to draw in fluid as they move toward the swash plate and discharge it as they move away. For a given speed swash plate pumps can be of fixed displacement like this one, or variable by having a variable swash plate angle. The greater the slant the further the pistons move and the more fluid they transfer.

Maintenance - Selecting the correct mineral-based oil

• With the help of product data sheet and OEM approvals and requirements

• Properties to consider:• Lifespan • Demulsibility properties• Right balance of corrosion inhibitors

• Fluid’s ability to release air quickly is important so pumps are

• protected from cavitation

A bypass valve is combined with spring loaded shock valves which open in the event of a very heavy sea forcing the rudder over. in moving over, the pump is actuated and the steering gear will return the rudderto its original position once the heavy sea has passed. a spring loaded return linkage on the tiller will prevent damage to the control gear during a shock movement. During normal opertion one pump will be running. if a faster response is required, for instance in confined waters, both pumps may be in use. the pumps will be in no-delivery state from the bridge telemotor transmitter. the telemotor receiver cylinder will then move: this will result in a movement of the floating lever which will move the floating ring or slipper pad of the pump, causing a pumping action. fluid will be drawn from one cylinder and pumped to the other, thus turning the tiller and the rudder. a return linkage or hunting gear mounted on the tiller will reposition the floating lever so that no pumping occurs when the required rudder angle is reached.

References

• McGeorge, H.D. Marine Auxiliary Machinery. Oxford: Butterworth-Heinemann,

1995. Print

• http://weh.maritime.edu/campus/tsps/manual/steering3.html