203d - Fuel System Service Flashcards
A micron is ______ of a meter?
1 millionth of a meter
0.000001m
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How wide is a human hair in microns?
70 microns
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What is the smallest particle visible to the human eye?
40 microns
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In injection pumps and injectors, precision machined parts are fitted with how small of clearances?
1-3 microns
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What size of particles are the most damaging to fuel injection equipment?
5-20 microns
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What are four basic types of fuel filters?
- Screen / strainer
- Surface
- Depth
- Edge
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Where are screen type filters typically used?
Fuel tank inlet
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What type of filter element do surface type filters use?
Pleated paper
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What are two disadvantages of depth type fuel filters?
- Less efficient
- More expensive
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How do edge type fuel filters work?
Trap particles as the fuel flows over ledges.
No micron rating. Not a positive method of filtration.
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What are three common filter classifications?
- Primary (25 micron)
- Secondary (5 micron)
- Final stage
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What are the general properties of a primary fuel filter?
- Typically 25 microns
- First filter after fuel tank
- Intended to protect the transfer pump
- Usually under a vacuum
- May be combined with a water separator
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What are the general properties of a secondary filter?
- Typically 5 microns
- On the outlet side of transfer pump
- Under pressure
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What are the general properties of a final stage fuel filter?
- Typically 1 micron
- Located just before the injection pump
- Under pressure
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Oil filters incorporate a bypass valve as a safety feature if they become plugged.
Do fuel filters also contain a bypass valve?
No. All fuel must be filtered.
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When is the greatest chance for fuel system contamination to occur?
During refuelling or fuel filter maintenance.
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Is it better to pre-fill fuel filters or use the built-in hand priming pump?
Use the hand priming pump. Less chance of contamination.
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What would result from air entering the fuel system?
- Reduced volume of injected fuel
- Delayed injection timing
- Rough running engine
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What are five basic types of fuel transfer pumps?
- Diaphragm
- Plunger
- Hand primer
- Gear
- Vane/blade
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What causes a diaphragm pump to enter a neutral pumping state?
When the pressure on the outlet side equals the diaphragm spring force.
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How are diaphragm transfer pumps self regulating?
Diaphragm spring tension controls max pressure.
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What pressures do diaphragm fuel transfer pumps operate at?
- 3-5 psi operating pressure
- Max 10 psi
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Where are plunger type fuel transfer pumps typically mounted?
On the injection pump housing and driven by an eccentric on the pump camshaft.
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Fuel flow through a plunger type fuel transfer pump is controlled by a set of:
Check valves
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