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Glossary of terms you will come across during your Phase 2 training.

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Sometimes, course participants may feel they can add more to an explanation given in this glossary. In cases like this, they can add comments. See the comment at the bottom of this entry. (Please note: comments are only visible to registered users who are logged in.)
This is content over and above what is on the Phase 2 syllabus for CP Fitters.
It is sometimes posted on the site in order to help apprentices who may wish to find out a little more about certain topics or equipment that is covered during Phase 2.
Additional content will not appear in any Phase 2 examinations.
You need only view additional content if you want to broaden or deepen your knowledge about specific topics or pieces of equipment.

Example of Additional Content

During the Electrical Module, there is a learning unit called 'Lighting Circuits'. During this unit, you will build various wiring circuits. One such circuit is an indicator (turn signal) circuit.
This type of circuit originally used what was known as a 'hot-wire' flasher unit. Nowadays, these older type flasher units have been replaced by electronic version.
If you would like to learn more about these more modern units, there is a page of additional information with an overview, links to data sheets and a video of the operation of a typical electronic flasher unit:
Address bar in a browser windowThis is the part of a browser window into which you can type the URL (the web address) of a website. If you know the exact URL of a site, you should type it in here.

From the Aerial Platform Hire website:

Aerial Platform Hire is Ireland's leading work platform rental company. Founded in 1980 we offer for hire self propelled boom and scissor lifts manufactured mainly by JLG industries, the worlds largest manufacturer of powered access equipment. We also offer Telescopic Handlers from JLG and Manitou Buggiscopics. Hire is available from strategically located depots in Clane, Co. Kildare and Mallow, Co. Cork. We deliver machines throughout Ireland from both of these depots.


Across Flats. A term used to describe measuring a bolt head. Note: This term does not describe the shank of the bolt, just the head, and hence what size spanner is required to open the bolt:
Across the flats

A UK based engineering company established for over 45 years specialising in the manufacture of vocational automotive related training products.
They supply to motoring organisations, technical colleges, diagnostic equipment manufacturers, motor manufacturers, and Schools.

Visit their website


Absorbed Glass Matte (AGM) Batteries

AGM Batteries are lead acid batteries. They use a separator consisting of fiberglass between the plates to hold the electrolyte in its place with capillary action.

In other words, the electrolyte is not in free-flowing liquid form, it is held in these absorbent mats. This is a safer arrangement, as it makes the battery "spill proof" - an important feature in the event of an accident or the vehicle over-turning. This type of battery also has a lower internal resistance. This increases the output voltage, and decreases charging time, AGM batteries are also often referred to as 'maintenance-free'. 

All battery charging over a certain voltage causes significant gassing. In flooded lead-acid batteries, these gasses are vented to the atmosphere. This results in a loss of electrolyte, which must be replenished during routine maintenance.

AGM batteries recombine these gases produced internally, back into the electrolyte, thus eliminating the need for topping up the electrolyte level during routine maintenance, hence the term 'maintenance-free'. 

These batteries are often VRLA, meaning that, should excess gas pressure build up during charging/discharging, these gasses are vented to the atmosphere.

Air is a gas that is the main component of the earth's atmosphere. It is a mixture of many different gasses such as nitrogen (78%), oxygen (20%) and carbon dioxide (1%). There are much smaller traces of other gasses such as freon, neon, argon, helium, carbon monoxide and helium.

This is the number of parts of air mixed with 1 part of fuel in an engine. There is an ideal, or optimum or stoichiometric ratio, which is 14.7 parts of air to one part of petrol, or 14.5 parts of air to one part of diesel.

An air fuel mixture with more air is said to be a 'lean' mixture, and a mixture with less air is said to be a 'rich' mixture.


Do not confuse 'air gap' with 'spark gap', they are two entirely different things.

Air gap between a flywheel and an ignition coil.Air gap normally refers to the clearance between a revolving object and a stationary coil or pick-up sensor.

In the diagram on the right, we can see a magneto ignition coil and a flywheel. The correct air gap between them is 0.4 mm, with a tolerance of + or - 0.2 mm. This means that an air gap of between 0.2 mm and 0.6 mm is acceptable.

In magneto ignition systems, the air gap is the clearance between the laminated iron core of the ignition coil and the revolving flywheel which has a permanent magnet mounted on it.

In this case, the ignition coil is able to produce a HT spark because the magnetic lines of force from the permanent magnet on the flywheel move rapidly across the coil windings. This induces a current in the primary windings. When we suddenly open the circuit in the primary windings, the magnetic field associated with the current in the primary windings collapses, inducing the HT spark in the secondary windings.

The air gap between the coil and the magnet on the flywheel is vital if we are to produce a good quality HT spark.

If the air gap is too small, the flywheel can physically contact and damage the laminated iron core of the ignition coil. This is a common fault in small plant petrol engines. Always check this gap during service.

If the air gap is too big, the magnetic lines of force (magnetic flux) tend to splay out into space, and do not act on the windings of the ignition coil, thus causing the coil to produce a weak spark.

Other components where air gaps are essential are items such as inductive ABS wheel sensors. If the air gap is too large, the sensor is incapable of producing a signal of sufficient amplitude, and this will cause the control system to log a fault code and to display a warning lamp.

See also: 'spark gap'

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