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Maritime Forum

TOPIC: Electro hydraulic gear

Electro hydraulic gear 28 Mar 2017 05:11 #4769

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With reference to electro hydraulic gear:

(a) Why pump is constant speed variable stroke.

(b) Describe two ways where by air enters in such system.

(c) Describe effect of air in system.

(d) Explain the system of telemotor receiver.
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Electro hydraulic gear 08 Jun 2017 01:09 #4843

1) As the steering gear is given different helm angle to turn the steering gear hydraulic system will require variable amount of the hydraulic fluid to turn the Rudder into the desired helm angle. The variable displacement pump can very easily cope up this continuous change in demand. Thus it is used for the purpose.

a} Low level of Oil level in the tank and a leaky connection in the suction side of the hydraulic pump can lead to air entering in the hydraulic system.
b} Foaming on the surface of the oil will also lead to the air entrapment in the system.

Problems resulting from air in the system has the following major effects:

Spongy control — Because fluids are considered to be basically incompressible, we expect great stiffness in a hydraulic system. That is, the positioning of an actuator should be immediate (rapid response) and precise. The larger the amount of free or entrained air, the spongier (softer, less stiff) the system.

Relatively low air pressures force substantial volumes of air into solution with MIL-H-5606 fluid. | Effect of a vacuum over MIL-H-5606 fluid that is saturated with air. The vacuum withdraws large quantities of dissolved air. Higher temperatures release more air. (click to enlarge)

Loss of horsepower — When an air pocket is present in an actuator, it is alternately compressed and relaxed as the actuator is cycled. Since the air pocket must first be compressed before the fluid can cause the actuator to move, power is consumed. Upon relaxation, the air pocket expands and rives fluid out. The stored power, therefore, is expended in driving fluid back into the reservoir and not in moving the actuator.

Loss of bulk modulus — Free or entrained air in the hydraulic system reduces substantially the effective bulk modulus of the system. That is, an air-oil mixture appears to increase the compressibility of the fluid, making the system spongy.

d) The telemotor receiver gets an electrical signal from Telemotor transmitter (located in wheelhouse) which is proportional to the helm angle required (i.e the angle of rudder desired) and it converts this electrical signal to a proportional mechanical motion of a plunger which then further pushes the swash plate of the variable displacement pump to pump the hydraulic fluid in the hydraulic rams of the steering gear.
Last Edit: 08 Jun 2017 01:11 by anandgardener.
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