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4. Make up the questions of all types to the text. (7)

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Text d solenoids and relays

Two definitions are in order because many people incorrectly use the term solenoid interchangeably with the term relay. About all they have in common is that both rely on an electromagnetic coil for operation.

A solenoid is an electromechanical device consisting of an electromagnetic coil surrounding a movable metal core or plunger. When the coil is energized, the magnetic field pulls the core until it's centered in the coil. Usually, there's a return spring to pull the core back to the uncentred position when the coil is shut off. The movable core can be connected to various mechanisms that move each time the magnetic coil is energized.

A relay is an electromechanical device consisting of an electromagnetic coil, a fixed core and a movable armature. The armature, attracted by magnetism in the core, moves whenever the coil is energized.

The distinguishing feature, then, is the core. In a solenoid, the core moves to do the work. In a relay, the core remains stationary and the armature moves.

Exercises Unit 6 (text d)

1. Put the phrases in right order to make up a dialogue “Relays”.

1. By means of a relay electric current flowing in one circuit can open or close a second circuit and thus control the switching on and off a circuit.

2. What are relays designed for?

3. I am very thankful for such exact information.

4. What device are called relays?

5. By the way what parts does relay consist of?

6. Relays are designed for rather low currents and for operation in control circuit at low voltages.

7. The main components of a relay are an electromagnet, an armature and a spring.

8. Can you explain the function of relays for me? I am very interested in it.

9. Relays are electromagnetic devices widely used in various branches of industry.

a) _____ b) _____ c) _____ d) ______ e) ______

f) ______ g) _____ h) _____ i) _______

2. Fill in the gaps with a suitable word from the list: a) tractor b) pumps c) pressure d) starting e) contain f) operated

1. The diesel fuel system operates under two _______ levels. The low pressure part of the system contains the fuel tank, fuel ______ and fuel filters. The high pressure part of the system ______ the injection pump, the high pressure lines leading to the injection nozzles.

2. We know some diesels to employ auxiliary gasoline engines for ______. These engines are used to crank the diesel until it starts. Most farm ______ diesels use electric starting motors similar to those used on gasoline engine tractors. They are _______ from the battery on the tractor.