## Monday, 14 December 2015

We have discussed in our previous post about the E O T crane and it’s Maintenance, and we have also seen how to inspect a gearbox.

Let us see a very interesting article Electric hydraulic thrusters and its working principle. Before few years, I have attended one technical interview and interviewer had asked me about the working principle of electric hydraulic thrusters. Unfortunately i was not aware at that time about the working principle of electric hydraulic thrusters and i was rejected at that time.

I have studied and seen the operation of electric hydraulic thrusters and decided to write one post about the working principle of electric hydraulic thrusters.

So let us come to the main topic i.e. working principle of electric hydraulic thrusters.

### Electric Hydraulic thrusters: overview

Electric hydraulic thruster is a device which works by taking electrical energy as input and converts electrical energy into mechanical energy to provide the linear motion. Electric hydraulic thruster will have following key components as mentioned here.
1. 3 Phase electric motor
2. Piston
3. Closed type of impeller, which will be driven by electrical motor
4. Oil sump, transformer oil will be used in thruster oil sump to work as working fluid

### Working principle of electric hydraulic thrusters

Impeller will be fixed with motor rotor. Electric motor will rotate the impeller when electric supply will be provided and impeller will generate the hydraulic pressure below the piston and therefore there will be produced one upward direction hydraulic force and this hydraulic force will be exerted below the piston.

As we know that
Force = Area x pressure

So, amplitude of hydraulic force will be dependent on the intensity of hydraulic pressure and area of piston. Piston will move in upward direction as shown in figure. When power supplied will be off, pressure will be relieved and piston will come to its original position due to the action of counter weight of springs.

### Application of electric hydraulic thrusters

I have mostly seen the application of electric hydraulic thrusters in drum brake mechanism in EOT crane and in ship or barge unloading crane also. When power supply will be given to electric motor of thruster, as we have discussed in working principle of electric hydraulic thruster , piston will move in upward direction and lifting movement of piston of thruster will operate the drum brake mechanism and brake shoes of brake mechanism will allow the drum to rotate.

When power supplied will be off, in that case piston will come to original position under the action of counter weight springs and therefore brake shoes will be pressed against drum of brake mechanism and therefore brake drum will not be able to rotate. Hence brake will be applied and motion of driver will be stopped by the drum brake mechanism.

### Advantage of using electric hydraulic thrusters

1. Installation and maintenance are quite easy
2. Service life is good
3. Power consumption is also low
4. Smooth movement of piston provides the jerk free thrust

### Key note

Oil must be filled of good quality transformer grade oil by top oil filling plug until oil overflow.

#### Important list of spares, as mentioned below, that must be available in stock

1. Impeller
2. Electric terminal box
3. Transformer oil
4. Respective Bearings
5. Oil seals
Do you have suggestions? Please write in comment box